Power Systems Pune University MCQs
Power Systems Pune University MCQs
This set of Power Systems Multiple Choice Questions & Answers focuses on “Introduction of Hydroelectric Power Plant”.
1. Which of the following is the correct equation for the electrical power generated by the hydroelectric power plant?
a) 75×0.736 wQHη Watt
b) × wQHη Watt
c) 0.845 ×wQHη Watt
d) 9.81 ×wQHη
Answer: c
Explanation: Rating of any power plant is expressed by its maximum output power. These are large quantities so rating is given in mega watts.The electrical power generated by this plant is proportional to specific weight of water, water head, generation efficiency, flow rate of water and acceleration due to gravity.
2. Which of the following is not a requirement for site selection of hydroelectric power plant?
a) Availability of water
b) Large catchment area
c) Rocky land
d) Sedimentation
Answer: d
Explanation: Sedimentation may reduce the water storage capacity of reservoir and may also cause damage to the turbine blades. Availability of water, large catchment area and rocky land are primary requirements for site selection of hydroelectric power plant.
3. The amount of electrical energy that can be generated by a hydroelectric power plant depends upon ___________
a) Head of water
b) Quantity of water
c) Specific weight of water
d) Efficiency of Alternator
Answer: b
Explanation: Potential energy of large quantity of stored water is used by hydroelectric power plant to generate electrical energy. Head of water is important to get kinetic energy from that potential energy. Efficiency of alternator represents that what percentage of input mechanical power it can convert into electrical power.
4. Potential energy of water is used to drive the turbine.
a) True
b) False
Answer: b
Explanation: When water falls, potential energy of water is converted into kinetic energy. This kinetic energy is used to drive the turbine.
5. Hydroelectric power plant is __________
a) Non-renewable source of energy
b) Conventional source of energy
c) Non-conventional source of energy
d) Continuous source of energy
Answer: b
Explanation: Hydroelectric power plants are conventional source of energy. About 16.6% of total electricity and about 70% of total renewable energy of world is provided by hydroelectric power plants. They are not Non-renewable because water is inexhaustible. It is not continuous source of energy because its output fluctuates with change in flow rate of water with season.
6. Hydroelectric power plant is generally located near load centre.
a) True
b) False
Answer: b
Explanation: Hydroelectric power plants are generally constructed in hilly areas. These power plants are quite away from the load centre.
7. Hydroelectric power plant is mainly located in ____________
a) Flat areas
b) Deserts
c) Hilly areas
d) Deltas
Answer: c
Explanation: In order to get sufficient head, hydroelectric power plants are constructed in hilly areas. In desert and flat areas sufficient water head cannot be obtained. Deltas are not suitable for this because of high sedimentation.
8. Which statement about hydroelectric power plant is wrong?
a) Efficiency of hydroelectric power plant does not reduce with age
b) Its construction coast is very high and takes a long time for erection.
c) It is very neat and clean plant because no smoke or ash is produced.
d) Meeting rapidly changing load demands is not possible in hydroelectric power plant.
Answer: d
Explanation: Fluctuating load demands can be met just by controlling the flow of water using valves and gates. Due to its robust construction, its efficiency does not fall with time. Statement ‘b’ is correct because construction of dam, installation of alternator and turbines are very costly.
9. Which of the following is not an advantage of hydroelectric power plant?
a) no fuel requirement
b) low running cost
c) continuous power source
d) no standby losses
Answer: c
Explanation: Output of such plants is never constant. This is because of their dependency over flow rate of water in river which is seasonal. No fuel requirement low running cost and no standby losses are advantages of hydroelectric power plants.
10. Which of the following statement is true about hydroelectric power plant?
a) Hydroelectric power plants are multipurpose.
b) Due to non-uniform flow of water frequency control in such plants is very difficult.
c) Hydroelectric power plant has high running cost
d) Water is used as fuel in hydroelectric power plant
Answer: a
Explanation: It is because in addition to generation of electricity they are also used for irrigation, flood control etc. Frequency control in such plants is done easily just by controlling flow of water to the turbine through valves and gates. Due to low maintenance cost and no fuel requirement running cost of a plant is very low. Water is not fuel.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Elements of Hydroelectric Power Plant”.
1. Which element of hydroelectric power plant prevents the penstock from water hammer phenomenon?
a) Valves and Gates
b) Draft tubes
c) Spillway
d) Surge Tank
Answer: d
Explanation: Sudden increase in water pressure in penstock due to closing of gates is called water hammer. Surge tank is a tank at sufficient height , connected to penstock through riser pipe. It takes the rejected water and relives the penstock from excessive water hammer pressure.
2. Dam having very wide base as compared to its height is called _________
a) buttress dam
b) arch dam
c) earth dam
d) solid gravity dam
Answer: c
Explanation: Buttress dams are the concrete dams supported on downstream side by buttresses. Arc dams are concrete dams curved from upstream side. Earth dam is a type of embankment dam and have rock filled inside the structure.
3. Spillway discharges the overflow water to the downstream side when the reservoir is full.
a) True
b) False
Answer: a
Explanation: A condition may arise during flood periods when water level increases beyond the capacity of reservoir. In such conditions spillway acts as safety valve.
4. Trash racks are built for ___________
a) discharging the water freely from the turbine exit to tailrace
b) preventing the turbine from ingress of floating and other materials
c) creating artificial head to store sufficient potential energy of water
d) controlling the opening of valves
Answer: b
Explanation: Heavy solid materials flowing with water can damage the turbine blades if not stopped. Trash racks are closely spaced flat bars which provides narrow path from which such unwanted materials cannot pass.
5. Penstock in a hydroelectric power plant is _____________
a) a pipe connected to runner outlet
b) nozzle that release high pressure water on turbine blades
c) a conduit connecting forebay to scroll case of turbine
d) a pipe connecting surge tank to dam
Answer: c
Explanation: Penstocks are the conduit built of steel or reinforced concrete. Penstock connects forebay or surge tank to scroll case of turbine. Their main function is to carry water from dam to the turbine.
6. The pressure at the inlet or exit of the draft tube should not be _________
a) less than one third of atmospheric pressure
b) greater than one third of atmospheric pressure
c) less than one atmospheric pressure
d) greater than one atmospheric pressure
Answer: a
Explanation: Decrease in pressure in any portion of turbine below one third of atmospheric pressure may cause vapour bubbles or cavities to form. This phenomenon is called cavitation. Also to maintain continuity of flow without vaporisation the pressure should not fall below vapour pressure of water.
7. Draft tube increases the operating head on the turbine.
a) True
b) False
Answer: a
Explanation: Draft tubes are the pipes of suitable diameter attached to the runner outlet. Draft tube converts the pressure developed by water leaving from turbine into kinetic energy. This in turn increases the operating head on turbine.
8. Which statement about surge tank is wrong?
a) Ideal location of surge tank is at the turbine inlet
b) A decrease in load demands cause a rise in water level in surge tank
c) Surge tanks are totally closed to avoid entry of unwanted objects to penstock
d) Surge tanks are installed to reduce harm effects of water hammer phenomenon
Answer: c
Explanation: Function of surge tank is to relieve the penstock from excessive water hammer pressure. It does so by receiving rejected flow of water into the tank. A totally closed tank can not release pressure so usually surge tanks are left open at the top.
9. Trash racks are located _____________
a) near tailrace
b) at the entrance of turbine
c) inside penstock
d) intake
Answer: d
Explanation: Intake includes headworks at the entrance of conduit. Those headworks include different structures, trash racks are one of them. Trash racks are fitted directly at the intake to prevent the floating and other materials from going into the conduit.
10. What is the function of booms?
a) It supports the dam
b) It supports the penstock
c) It divert the Icebergs from flowing into the penstock
d) To hold the turbine structure
Answer: a
Explanation: Booms are the one of those structures made at the intake. They are constructed to prevent unwanted solid materials from flowing into the penstock. Solid materials like icebergs, wood logs or other heavy materials which may cause damage to the turbine blades if reached there.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Water Turbines”.
1. Kaplan turbine is _____________
a) axial flow turbine
b) inward flow turbine
c) tangential flow turbine
d) mixed flow turbine
Answer: a
Explanation: In Kaplan turbine water strikes the turbine blades axially. That’s why Kaplan turbine is an axial flow turbine. Kaplan turbines are special type of turbines for low head applications.
2. Pelton turbines are used for __________________
a) medium head applications
b) low head applications
c) in steam power plants
d) for high head applications
Answer: d
Explanation: Pelton turbines are impulse turbines and are suitable for high head low flow plants. Pelton turbines consist of elliptical shaped buckets along its Periphery. Water is released from nozzle to the buckets of turbine.
3. Francis turbines are the type of _____________
a) reaction turbines
b) radial flow turbine
c) impulse turbine
d) axial flow turbine
Answer: a
Explanation: Francis turbines are inward mixed flow type reaction turbines. Such turbines develop power partly due to velocity of water and partly due to difference in pressure acting on the front and back of the runner blades.
4. Operating head of Francis turbine is __________
a) less than 30
b) less than 70 m
c) 30 to 200 m
d) more than 200 m
Answer: c
Explanation: Francis turbines are medium head and medium flow turbines. Using it for low or high head will cause inefficient operation. Their life is about decades so maintenance cost is low.
5. Which of the following is not a reaction turbine?
a) Francis turbine
b) Kaplan turbine
c) Pelton wheel turbine
d) Propeller turbine
Answer: c
Explanation: When the entire pressure of water is converted into kinetic energy in a nozzle and the jet thus formed drives the wheel then the turbine is called impulse turbine. Pelton turbine works in similar way, so it is an impulse turbine. Francis, Kaplan and propeller turbines are reaction turbines.
6. Inside pressure of which of the following turbine is equal to atmospheric pressure?
a) Fixed vane propeller turbine
b) Movable vane propeller turbine
c) Francis turbine
d) Pelton wheel turbine
Answer: d
Explanation: Francis and propeller turbines are totally submerged in water, the turbine casing is full of water. As the water flows through the turbine blades, its pressure changes. Also the discharging water creates negative pressure below the turbine blades. Pelton turbines are fitted in open air and water Jet is forced into its blades by nozzel so it’s inside pressure is equal to atmospheric pressure.
7. Francis turbine is suitable for medium head hydroelectric power plant.
a) True
b) False
Answer: a
Explanation: Francis turbines are medium head and medium flow turbines. Kaplan turbines are low head high flow turbines. Pelton turbines are high head and low flow turbines.
8. Which turbine has highest speed?
a) Pelton wheel turbine
b) Francis turbine
c) Impulse turbine
d) Kaplan turbine
Answer: d
Explanation: Francis turbine has a specific speed of 60 to 300 rpm. Specific speed of Pelton turbine is lowest. Speed of Kaplan turbine is 2 to 3 times more than that of Francis turbine.
9. Governing mechanism used in case of Pelton wheel turbine is ________
a) guide vane
b) nozzle needle
c) control valve
d) dam gates
Answer:b
Explanation: During load variation it is necessary to maintain the speed of the alternator constant. This is achieved by controlling the flow of water entering the turbine by the help of automatic adjustment of guide vanes for reaction turbine and the nozzle needle is in case of impulse turbine. Such an operation of speed regulation called governing and the system used to do this is called governor.
10. Guide vanes are used as governor in Kaplan turbine.
a) True
b) False
Answer: a
Explanation: Guide vanes are used as governor in Francis and Kaplan turbines. These guide vanes controls the flow of water to the turbine and hence governs the speed of rotation of turbine. Under different loading conditions the speed of rotation of turbine is needed to be controlled for constant frequency output.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Efficiency of Steam Power Plant”.
1. Which part of thermal power plant causes maximum energy losses?
a) Boiler
b) Alternator
c) Condenser
d) Ash and unburnt carbon
Answer: c
Explanation: About 54% of energy losses occurs in condenser. Losses in boiler and alternator are about 1% and 16% because of such high losses overall efficiency of thermal power plant reduces to 29% for normal old thermal power plant and 50% for modern super critical pressure steam power plant which employs many heat saving devices.
2. What is the effect of increasing steam pressure on efficiency of steam power plant?
a) Increases linearly
b) Increases nonlinearly
c) Decreases linearly
d) Does not changes
Answer: b
Explanation: The thermal efficiency of steam power plant depends upon the steam pressure. The efficiency increases with increasing steam pressure nonlinearly up to a level. After that level increase in efficiency becomes very low with respect to increasing pressure.
3. What is the effect of increasing steam temperature of thermal power plant on its thermal efficiency?
a) Increases linearly
b) Decreases
c) It does not depends on temperature
d) Increases nonlinearly
Answer: a
Explanation: Thermal efficiency of steam power plant increases with increase in steam temperature linearly. Increas in temperature of steam also causes its effect on cost. So temperature of steam is increased only upto a level at which it is economical.
4. Overall efficiency of thermal power plant is equal to ___________
a) Thermal efficiency
b) Generation efficiency
c) Multiplication of thermal and generation efficiency
d) Ratio of thermal and generation efficiency
Answer: c
Explanation: Thermal efficiency of steam power plant is the ratio of the heat equivalent of mechanical energy transmitted to the turbine shaft and the heat of the combustion. Thermal efficiency is generally quite low about 30%. Efficiency of generator is called generation efficiency.
5. In supercritical pressure steam power plant temperature of steam is __________
a) 480°C
b) 240°C
c) 600°C
d) 150°C
Answer: c
Explanation: At a temperature about 600°C water enters in supercritical phase and has property between those of liquid and gas. advantage of such plant are that low grade fossil fuel can be used. Efficiency of such plants may be reached up to 50%.
6. For increasing the thermal efficiency of thermal power plant pressure in condenser should be:
a) Reduced upto 0.04 kg/cm 3
b) Kept above 2.45 kg/cm 3
c) As high as boiler pressure
d) Same as atmospheric pressure
Answer: a
Explanation: The thermal efficiency can be effectively increased by decreasing the pressure in the condenser. Pressure in condenser is kept very low usually 0.04 kg/cm 2 .
7. Economisers are necessary to use for pressure of 70 kg/cm 2 or more.
a) True
b) False
Answer: a
Explanation: High cost of fuel consumption, high load factor and high pressure and temperature conditions, all justify the use of economiser. Installation of economiser involves extra cost of installation, maintenance and regular cleaning and additional requirement of space. By considering above points it has been found that use of economiser becomes necessary for pressure above 70 kg/cm 2 .
8. Supercritical pressure boiler scan produce steam at the rate of _________
a) less than 1,500 kg/hr
b) less than 340,000 kg/hr
c) less than 80,000 kg/hr
d) upto 1,000,000 kg/hr
Answer: d
Explanation: Modern supercritical pressure boiler with pressures as high as 350 atm temperature 600°C and capacity 1,000,000 kg/hour are available now days. Fire tube boiler can produce steam at the rate of 15,000 kg/hr. Water tube boiler can produce 340,000 kg of steam per hour.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Constituents of Steam Power Plant”.
1. What is the principle of operation of steam power plant?
a) Carnot cycle
b) Brayton cycle
c) Stirling cycle
d) Rankine cycle
Answer: d
Explanation: The Rankine cycle is an idealized thermodynamic cycle of heat engine. Under this cycle heat energy is converted into mechanical energy while undergoing phase change. The heat is supplied externally to the closed loop which usually uses water as working fluid.
2. Read the following statement about boilers.
I. Water tube boiler is capable of generating steam of pressure more than 50 kg/cm2 .
II. Fire tube boiler is suitable for generating steam of pressure less than 17.5 kg/cm2 .
III. Water tube boiler occupy comparatively less space.
a) Only statement I is true
b) Statement I, II and III are true
c) I and II are true but III is false
d) I and III are true but II is false
Answer: b
Explanation: In fire tube boiler water and steam are in same shell so higher pressure is not possible. In water tube boiler comparison to fire tube boiler, the drum do not contain any tabular heating surface so they can be built in smaller diameter and consequently they will withstand higher pressure.
3. Fire tube boilers are safer than water tube boilers.
a) True
b) False
Answer: b
Explanation: In event of sudden and major tube failure steam explosion may occur in furnace of fire tube boiler due to rush of high pressure water into hot combustion chamber. Water tube boiler does not contain such tubular heating surfaces so no such problem arises there.
4. Which of the following material is not used in the boiler furnace walls?
a) Fire clay
b) Concrete
c) Silica
d) Kaolin
Answer: b
Explanation: Fire clay, Silica and Kaolin have property of resisting change in shape, weight or physical property at higher temperature. Concrete have no such properties at higher temperature so it is not suitable for that. The construction of boiler furnace varies from plain refractory walls to completely water cooled walls depending upon the characteristics of fuel used and firing methods.
5. Which of the following statement about economiser of steam power plant is wrong?
a) Economiser increases the Boiler Efficiency about 5 to 15%
b) It uses the heat of flue gases used by boiler going to the chimney.
c) Economiser increases the temperature of intake air
d) It require regular maintenance and cleaning
Answer: c
Explanation: Economiser is used to rise the temperature of feed water. Air preheater is used to raise the temperature of intake air. Flue gases after heating boiler water Still possesses sufficient heat energy which if not used will waste. Economiser and air preheater uses that heat energy to work and hence increase the thermal efficiency of power plant about 15%.
6. Which of the following are the most widely used condensers in modern thermal power plants?
a) Surface condensers
b) Low level counter flow type jet condenser
c) High level counter flow type jet condenser
d) Parallel flow type jet condenser
Answer: a
Explanation: Power plants mostly use surface condensers because from these condensers condensate can be used as feed water requiring less pumping power. In case of jet condensers exhaust steam mixes with the cooling water hence condenses and cooling water are mixed so condensing cannot be recovered for the use of feed water.
7. Read the following statements about feed water heaters
I. Open or contact heaters are also called Deaerator.
II. Open or contact heaters constructed to remove non-condensable gases from feed water.
a) Only statement I. is correct
b) Only statement II. is correct
c) I. and II. are correct
d) I. and II. are wrong
Answer: c
Explanation: Dissolved gases can cause corrosion inside the boiler so they must be removed from feed water. Feed water heaters are used to heat the feed water by means of bled steam before it is supplied to the boiler. The amount of non-condensable gases decreases with increase in temperature of water in open heaters hence called Deaerator.
8. Which of the following is a part of air and fuel gas circuit?
a) Condenser
b) Economiser
c) Air preheater
c) Cooling tower
Answer: c
Explanation: In air and fuel gas circuit air is drawn from the atmosphere by a forced draught fan or induced draught fan through the air preheater. In air preheater that air is heated by the heat of flue gases passing to the chimney and then admitted to the furnaces. Cooling tower and Condenser are parts of Cooling water circuit and Economiser is part of Feed water and steam circuit.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Steam Turbines”.
1. Which of the following is not a type of steam turbine?
a) Impulse turbine
b) Reaction turbine
c) Pelton wheel turbine
d) Axial flow type turbine
Answer: c
Explanation: Pelton wheel turbine is a water turbine. Impulse and reaction turbines are the steam turbines characterized by the action of steam on moving blades. Axial and radial flow turbine and steam turbines are characterized by type of flow of steam over blades.
2. Which statement about impulse turbine is true?
a) Steam expands over blades
b) Steam expends completely in stationary nozzels
c) Steam expends partially over nozzle and turbine blades
d) Steam expends over blades incompletely
Answer: b
Explanation: In an impulse turbine the steam expands completely in the stationary nozzles. No pressure drop occurs over the moving Blade Runner. During expansion steam attains a high velocity and impinges against the blades fixed on the rotor Periphery resulting in the impulsive force on the moving blades which sets the rotor rotating.
3. Which statement about reaction turbine is false?
a) Steam does not expand in nozzle
b) Blades acts like nozzles
c) Steam expands as flows over the rotor blades
d) Steam continuously losses its heat as flows over the rotor blades
Answer: d
Explanation: The expansion of steam in reaction turbine totally occurs when it flows over the turbine blades. The expansion of steam as it flows over the blades is adiabatic any friction losses between the steam and the blades are converted into heat which in turn will reheat the steam.
4. Reaction turbines are characterized by ___________
a) relatively low RPM and steam expension over nozzle
b) relatively high RPM and steam expension over nozzle
c) relatively low RPM and steam expension over rotor blades
d) relatively high RPM and steam expansion over rotor blades
Answer: c
Explanation: In reaction turbine steam does not expand in nozzle but expands as flows over the rotor blades. Reaction turbines are characterized by relatively low RPM. As steam expands over the turbine blades, causes the reaction force over the turbine which rotates the turbine.
5. In condensing turbine what is the back pressure of the turbine?
a) Very high
b) Above atmospheric pressure
c) Equal to atmospheric pressure
d) Below atmospheric pressure
Answer: d
Explanation: According to the back pressure steam turbines are classified into condensing and non condensing turbines. Where there is no use of exhaust steam, turbine is built as a pure condensing type turbine. In condensing turbine steam is reduced in pressure down to a vacuum pressure which is in accordance with the cooling water temperature.
6. The turbine in which steam enters the blade tip nearest the axis of the wheel and flows towards the circumference is called _____________
a) axial flow turbine
b) radial flow turbine
c) impulse turbine
d) non-condensing turbine
Answer: b
Explanation: According to type of flow of steam the steam turbines used are of two types namely axial flow turbine and radial flow turbine. In axial flow turbine steam flows over the blades in a direction parallel to the axis of wheel. In radial flow turbine steam enters from blade tip near the axis of wheel and flows towards the circumference.
7. Majority of the turbines are axial flow type.
a) True
b) False
Answer: a
Explanation: In axial flow type turbines the steam flows over the blades in a direction parallel to the axis of the wheel. In radial flow turbines the blades are arranged radially so that the steam enters at the blade tip nearest the axis of the wheel and flows towards the circumference.
8. Which turbines are employed for driving alternator at synchronous speed?
a) Central Station turbine
b) Reheating turbine
c) Extraction turbine
d) Extraction induction turbine
Answer: a
Explanation: Central turbines are for driving the alternator at synchronous speed. In Reheating turbine steam is returned back to the boiler after partial expansion for superheating and then allowed to expand to back pressure. In extraction turbines steam leaves the turbine casing before the exhaust, for feed water heating.
9. Read the statements below.
I. The built up rotor is cheaper and easier to manufacture.
II. The high pressure and intermediate pressure rotors are always of integral type.
a) Only statement I is correct
b) Only statement II is correct
c) I and II are correct
d) I and II are wrong
Answer: c
Explanation: A built-up rotor consists of a forged steel shaft on which separate forged steel discs are shrunk and keyed. In an integral rotor the wheels and shaft are formed from the solid forging. The built-up rotor is cheaper and easier to manufacture.
10. In velocity compounding the steam is expanded from the boiler pressure to condenser pressure in one set of stationary blades on nozzle.
a) True
b) False
Answer: a
Explanation: In compounding a number of rotors in series, keyed on the same shaft, are employed and the steam pressure or the jet velocity is absorbed in steps as it was over the moving blades. Compounding is necessary for obtaining reasonable blade tip speed in turbines.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Fuels”.
1. Which of the following is correct arrangement of different types of coals according to their increasing carbon content?
a) Peat, bituminous, lignite, anthracite
b) Peat, lignite, bituminous, anthracite
c) Bituminous, peat, lignite, anthracite
d) Peat, anthracite, bituminous, lignite
Answer: b
Explanation: Coal is the most commonly used fuel in thermal power plant. Coal contain moisture, carbon, hydrogen, sulphur, Nitrogen, Oxygen and ash. Coals are classified according to their calorific value and carbon content.
2. Which of the following is most suitable fuel for thermal power plant?
a) Peat coal
b) Lignite coal
c) Bituminous coal
d) Anthracite coal
Answer: c
Explanation: Peat and lignite coals have low calorific value and high ash content. Anthracite coals are found in small quantities and are therefore costlier for power generation. Bituminous coals have enough calorific value, low moisture and ash content so most suitable for power generation.
3. Read the below statements.
I. Sulphur is one of the combustible elements
II. The Sulphur content of coal should be less than 1%
a) Only I is correct
b) Only II is correct
c) I and II are correct
d) I and II are incorrect
Answer: c
Explanation: Sulphur content is one of the factors taken into account while selecting coal for steam power plant. Sulphur is combustible element and can produces energy. But its primary combustion product, Sulphur dioxide, is a health hazard due to which sulphur content in coal should be low.
4. Which of the following coal has highest moisture content?
a) Sub-bituminous coal
b) Bituminous coal
c) Anthracite coal
d) Peat coal
Answer: d
Explanation: Peat is the first stage in the process of transformation of buried vegetation into coal. It has about 60% to 90% moisture content and low carbon content . Peat coal is not suitable for use in power plants.
5. Which of the following coal has highest enthalpy of combustion?
a) Peat coal
b) Sami-bituminous coal
c) Semi-anthracite coal
d) Lignite coal
Answer: b
Explanation: Peat and lignite coals have enthalpy of combustion about 3000 KJ/kg and 17600 KJ/kg. Semi-anthracite coals are harder than bituminous coals and have enthalpy of combustion up to 34750 KJ/kg while sami bituminous coals have that up to 35000 KJ/kg.
6. What is the main drawback of liquid fuel in thermal power plant?
a) High handling cost
b) Hard and Adhesive oil slag
c) Difficult to store
d) High cost of liquid fuel
Answer: d
Explanation: Handling and storing cost of oil fuels are less, load fluctuations can be made easily and few operations are needed. There is no disposal of ash. Superheaters are subjected to hard and adhesive oil slag which is often difficult to remove, but other heating surfaces are almost trouble free.
7. A minimum of 4 to 6 percent of ash is required in coal.
a) True
b) False
Answer: a
Explanation: This 3 to 6% of ash is required on hand fire grates and some stokers for protection of grades against overheating.
8. Grindability of coal should be low.
a) True
b) False
Answer: b
Explanation: Grindability index is inversely proportional to the power required to grind the coal to a certain fineness. Higher the grind ability factor index better the coal is.
9. The selection of coal for power plant does not depends on _________
a) Calorific value
b) Nitrogen content
c) Sulphur content
d) Grindability index
Answer: b
Explanation: The selection of coal for power plant depends on the number of factors such as calorific value, weather ability, sulphur content, ash content, particle size, grindability index, and caking characteristics. Nitrogen content is not needed for the selection of coal for power plants.
10. Read the following statements about coals.
I. Lignite coals can be used in thermal power plants
II. Super-anthracite coal are best for thermal power plants
a) Only I is correct
b) Only II is correct
c) I and II are correct
d) I and II are incorrect
Answer: a
Explanation: Lignite have 30 to 50% moisture and 20 to 40% carbon content and can be used in power generation. Super-anthracite coals are very hard with shiny black surface. It is non cooking and is very difficult to ignite and so, it has little importance in power generation.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Fuel Combustion and Combustion Equipments”.
1. Which of the following is not an advantage of stoker firing?
a) Zero capital investment
b) Greater combustion capacity
c) Uniform feeding of coal into furnance
d) Saving in labour cost
Answer: a
Explanation: Stokers are the mechanical arrangement which is used to feed coals into the furnace. Due to the mechanical equipment combustion capacity increases with uniform feeding of coal of into furnace, also labour cost is reduced. Stoker firing requires installation of mechanical stoker hence, capital investment requires.
2. In case of underfeed stokers fuel is supplied in the furnace _________
a) below the point of air admission
b) above the point of air admission
c) beside the point of air admission
d) by shovels
Answer: a
Explanation: Mechanical stokers are of two types namely underfeed stokers and overfeed stokers. The two differ in manner of feeding of coal below or above the level at which primary air is admitted in the furnace. In case of underfeed stokers fuel is supplied into the furnace below the point of air admission.
3. Which of the following is most advantageous and most widely method of solid fuel firing?
a) Stoker firing
b) Underfeed firing
c) Spreader stoker firing
d) Pulverised fuel firing
Answer: d
Explanation: The advantages of using pulverised fuel outweigh the disadvantages and all the modern power plants uses pulverised fuel firing method. In pulverised fuel firing better combustion is achieved. Pulverization is a means of exposing a large surface area to the action of oxygen and consequently helping the combustion.
4. What is the main disadvantage of spreader stoker?
a) Poor control
b) Difficult operation
c) More unwanted fly ash
d) Dangerous operation
Answer: c
Explanation: In spreader stoker the coal is not fed into the furnace by means of grate. Coal is fed by means of hopper, and function of grade is only to collect and remove the ash out of furnace. Spreader stokers can burn any type of coal from lignite to samianthracite, whether they are free burning or cocking. Their disadvantage is that fly ash is more.
5. Which do you mean by pulverization?
a) Burning of crushed coal
b) Burning of uncrushed coal
c) Crushing of coal into small partials
d) Breaking coal into small particsl
Answer: c
Explanation: Pulverization is crushing of coal into fine particles. This exposes large surface area to the action of oxygen and consequently helps the combustion. Solids fuels can be used in a powderd and burn like oil and gas.
6. What is the amount of air required to burn the pulverised coal?
a) Less than air required to burn lumped coal
b) More than air required to burn lumped coal
c) More than air required to burn lumped coal
d) No air required to burn the lapped coal
Answer: a
Explanation: The surface area of pulverised coal is increased in almost the ratio of 400:1, therefore high rates of combustion are possible. Moreover a smaller quantity of air is required than when the fuel is burnt in lumped form.
7. Capital cost of pulverised fuel firing is less than hand firing.
a) True
b) False
Answer: b
Explanation: Hand firing does not require any capital investment. For pulverised fuel firing separate coal preparation plant is required which makes the installation expensive.
8. What is the main requirement of good coal burner?
a) Minimum operating and maintenance cost
b) Production of uniform flame with complete combustion
c) The burner should be easy to handle and control
d) Attainment of proper designed
Answer: b
Explanation: Main requirement of good coal burner is complete combustion with production of uniform flame. Minimum operating and maintenance cost, simplicity in operation, attainment of proper design all are requirements of complete combustion.
9. Coal burners are employed to fire the pulverised coal along with primary air in the furnace.
a) True
b) False
Answer: a
Explanation: Coal burner’s fire pulverised coal with stream of primary air into the furnace. Secondary air is then admitted separately below the burner, around the burner or elsewhere.
10. Spread stockers can be employed for boiler capacitors of _________
a) 1000 kg/hr – 14000 kg/hr
b) 586 kg/hr – 1086 kg/hr
c) 1500 kg/hr – 40000 kg/hr
d) 70,000 kg/hr – 140,000kg/hr
Answer: d
Explanation: In spreader stoker coal is fed from the coal hopper into the path of the rotor by means of a conveyor and rotor throws the coal into the furnace. Grate collects the ash and moves it out of the furnace.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Feed Water”.
1. Which of the following is not a reason of heating feed water?
a) It improves overall efficiency
b) It removes dissolved impurities
c) It prevents from thermal stress which may cause due to enter of cold water into boiler
d) It produces steam from feed water
Answer: d
Explanation: Steam production is work of boiler. Feed water is heated only for four reasons : to improve overall efficiency, to remove dissolved impurities, to avoid thermal stress going to entering of cold water to the boiler and to precipitate impurities carried by steam and condensate outside the boiler.
2. Feed water for boiler of thermal power plant is obtained from:
a) Natural sources like river and lake
b) Partly from condensed steam and natural sources
c) Condensed steam and small percentage from natural resources
d) Natural sources and small percentage from condensed steam
Answer: c
Explanation: The steam coming out of turbines is condensed and the condenset is fed back to the boiler. Some of water losses due to the blow-down, leakage etc.. and to make up these losses additional water called “makeup water” is taken from natural sources after treatment. This makeup water is obtained from natural sources like river and lake and about 1 – 4% of total feed water.
3. Mechanical method of water treatment is done to _____________
a) Heat the feed water
b) To remove solid matter and impurities
c) To add some solid materials
d) To remove dissolved gases
Answer: b
Explanation: Mechanical method of water treatment involvs sedimentation and filtration. During sedimentation water kept at standstill or flow with a very low velocity which causes the solid matter to settle down and finally removed. During filtration the dirty water is allowed to flow downword through the beds of filtering materials to remove suspended matters.
4. Which method is used in large modern thermal power plants to heat feed water?
a) Open type heatre is used
b) Close type heater is used
c) Steam is directly taken from main turbine and used to heat it feed water
d) Surface type heater is used
Answer: c
Explanation: Open and contact type haters are in small power plants. Such heaters recives steam from back pressure turbine. In large modern power plants heaters bleed steam from the main turbine and use it for heating of feed water.
5. Thermal treatment methods used to remove impurities like:
a) Dissolved carbon dioxide and other gases
b) Solid materials
c) Carbonate
d) Bacterial impurities
Answer: a
Explanation: Thermal treatment method involves distillation and derative heating of feed water. During distillation water is evaporated then condensed and collected. During derating heating water is broken up into fine droplets and heated to produced vapour within the deaerator. During these process carbon dioxide and other days of devices separated from feet water.
6. Heat treatment arrangement used to separate or remove deserved gases and impurities from feed water is called the year later.
a) true
b) False
Answer: a
Explanation: A deaerator is a device that is widely used for the removal of oxygen and other dissolved gases from the feedwater to steam-generating boilers. These gases make house corrosion scale formation.
7. Chemical method of treatment is used for treatment of:
a) Diissolve gases
b) Carbonate and carbon dioxide
c) Bacterial impurities
d) Send and suspended materials
Answer: b
Explanation: Chemical treatment involvs line treatment, soda treatment, lime and soda treatment. Zeolite treatment and demineralisation. Iime treatment is done for treatment of carbonate hardness, carbon dioxide in water. soda treatment is done for treatment of water containing non carbonate hardness and line soda treatment is used when both carbonate and none carbonate hardness for feed water.
8. Scall formation in boiler tube causes ____________
a) reduction of heat transfer and overheating of boiler tube
b) corrosion of boiler surface
c) feeling up of steam passage
d) cracks in the ages rivites
nswer: a
Explanation: Dissolved gases include oxygen and carbon dioxide which may lead to scale formation corrosion, carry over and imbrittlement in boiler and other apprature. Scale formation reduces the heat transmission through the heating surface.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Introduction of Nuclear Power Plant”.
1. The best capable alternative source which can meet the future energy demand is _____________
a) thermal power plant
b) nuclear power plant
c) hydroelectric power plant
d) geothermal power plant
Answer: b
Explanation: Demand of electrical energy is increasing at fast rate owing to booming increase in the population and industrial growth. The reserves of fossil fuel i.e., coal, oil and gas are fast depleting. There are many alternative sources of energy but they are not enough to supply such huge demand, only nuclear power plants are capable of doing that.
2. How much coal is required to generate energy equivalent to the energy generated by 1 kg of uranium?
a) 30000 tonnes of high grade coal
b) 300 tonnes of high grade coal
c) 10000 tonnes of high grade coal
d) 3000 tonnes of high grade coal
Answer: d
Explanation: One of the main attention for nuclear fuel is the huge amount of energy that can be released from a small quantity of active nuclear fuel. The energy obtainable by completely using 1 kg of Uranium would give energy equivalent 3000 tons of high grade coal i.e. Uranium has three millions times the energy of coal.
3. Nuclear fuel in reactor lasts for ________________
a) more than 5 months
b) few weeks
c) few days
d) more than 5 years
Answer: d
Explanation: Very small amount of nuclear fuel can produce very high amount of energy. Nuclear fuel may remain in a reactor for more than 5 years.
4. Cost of nuclear fuel in nuclear power plant economics is considered as __________
a) running cost
b) maintenance cost
c) capital cost
d) development cost
Answer: c
Explanation: Nuclear fuel in a nuclear reactor may remain for more than 5 years. So the cost of fuel injected initially is taken as capital cost and may be a few crore rupees.
5. In economics of nuclear power plant taxes and insurance charges are taken as _______
a) operating cost
b) maintenance cost
c) capital cost
d) fixed cost
Answer: d
Explanation: The life of reactor plant may be taken as between 15 to 20 years. For the other parts of the plant equipment the life may be taken as 30 years. The fixed cost would be interest, depreciation, taxes and insurance charges.
6. Which of the following are not taken as operation and maintenance cost in economics of nuclear power plant?
a) Taxes and insurance
b) Salaries and wages of staff
c) Cost of waste disposal
d) Cost of processing materials
Answer: a
Explanation: Taxes and insurance are taken as fixed costs. Salaries and wages of operation and maintenance staff, cost of waste disposal and cost of processing materials are the operation and maintenance cost.
7. What is the overall efficiency of nuclear power plant?
a) 20 to 25%
b) 25 to 30%
c) 30 to 40 %
d) 50 to 70 %
Answer: c
Explanation: The overall efficiency of a nuclear power plant is around 30 to 40%. Efficiency is higher at high road factors. Therefore, a nuclear power plant is always operated as a base load plant.
8. The land area required for installation of nuclear power plant is ________
a) more than thermal power plant
b) less than thermal power plant
c) equel to thermal power plant
d) depends on type of construction
Answer: c
Explanation: Nuclear power plants need less area as compared to any other plant of same generation capacity. A 2000MW nuclear power plant needs about 80 acres whereas the coal fired steam power plant of same generation capacity needs 250 acres of land.
9. All of the nuclear fuel reserve will be ended in about 400 years.
a) True
b) False
Answer: b
Explanation: There are larger deposits of nuclear fuel available all over the world. Therefore, such plants can ensure continued supply of electrical energy for thousands of years.
10. With respect to the load centre which location is suitable for stablishment of nuclear power plant?
a) Load centre
b) Near load centre but at reasonable distance
c) Far away from load centre
d) Near chemical industries
Answer: b
Explanation: These plants can be located near the load centre because of the negligible cost of transportation of fuel. But there should be a reasonable distance between the nuclear power plant and the nearest populated areas from point of view of safety against danger of radioactivity. It is highly undesirable to choose a site adjacent to chemical industries oil refineries PWD works hospitals and schools.
11. Operating cost of nuclear power plant is less than thermal power plant.
a) True
b) False
Answer: a
Explanation: Cost of fuel in nuclear power plant is taken as the capital cost. The the total operating cost involves wages and the salaries of operating and maintenance staff only, cost of disposal of waste etc.. The cost of transport and handling of coal for conventional thermal power plant is much higher than the cost of nuclear fuel.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Nuclear Reaction”.
1. In nuclear power stations which nuclear reaction is performed?
a) Nuclear fission
b) Nuclear fusion
c) 90% fission and 10% fusion
d) 90% fusion and 10% fission
Answer: a
Explanation: Nuclear fission is the process in which heavy nucleus is split when it is bombarded by certain partials. Huge amount of energy is released during nuclfclear fission in form of heat and radiation.
2. Which particle is bombarded on heavy nucleus of nuclear fuel?
a) Electron
b) Proton
c) Neutron
d) Photon
Answer: c
Explanation: Nuclear fission involvs bombardment of certain particles on heavy nucleus causing it to split. All modern fission reactors uses neutron particles for this purpose because they are neutral in charge and so, they can make their way through the shells of electrons and then through the nucleus at low energy.
3. The critical mass for U235 fission reaction is about _____________
a) 100Kg
b) 200 Kg
C) 50 kg
d) 10 kg
Answer: d
Explanation: For a chain reaction to occur the sample of the fissionable material should be large enough to capture the neutron internally. The minimum mass of fissionable material required to sustain a chain reaction is called the Critical Mass”. The critical mass varies for each reaction, for U235 fission reaction it is about 10 Kg.
4. The fuel mainly used in nuclear fission reactors are:
a) U235
b) U239
c) U233
d) U238
Answer: a
Explanation: The materials U235,U233 and Pu239 are called fissionable materials. From all the above mentioned fuels only U235 will fission in chain reaction.
5. Which fissionable nuclear fuel occur in nature?
a) Plutonium
b) Thorium
c) Uranium
d) 94239 Pu
Answer: c
Explanation: The only natural fissionable fuel occurring in our nature is Uranium, of which 99.3% is U238 and 0.7% is U235 and U234 is only a trace. Out of these isotopes only U235 will fission in chain reaction.
6. Which of the following has high fission percentage?
a) Pu239
b) U233
c) U235
d) U234
Answer: c
Explanation: U235 has higher fission percentage in comparison to others. U235 is only fissionable nuclear fuel found in nature, Pu239 and U233 are produced artificially. They are fissionable.
7. Reactors used for converting fertile materials to fissile materials are called _____
a) research and development reactor
b) production reactor
c) power reactors
d) slow reactors
Answer: b
Explanation: Research and development reactors are used for testing new reactor designs and research. Production reactors are used for converting fertile materials into fissile materials and Power reactors are used for generation of electrical energy.
8. Which statement about fast reactor is true?
a) These reactors are big in size so not easier to shield
b) Fast reactors can convert fertile materials to fissile materials
c) Fast reactors are easy to control
d) Heat transfer and cooling is very easy and simple
Answer: b
Explanation: Fast reactors can convert more fertile material to fissile materials with the result that the net fuel consumption for such reactors is much less. These reactors are small and compact and so easier to shield. Heat transfer and cooling problems in the core are accomplished due to high power density.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Nuclear Reactor Main Parts and their Functions”.
1. In which part of nuclear power plant steam is produced?
a) Boiler
b) Heat exchanger
c) Chamber across the reactor
d) Air preheater
Answer: b
Explanation: There is no boiler in nuclear power plant. The heat energy released in the reactor during nuclear fission is utilised to heat the coolant. This coolant is circulated through the heat exchanger to produce steam.
2. What is the main function of moderator?
a) It absorb the extra neutrons
b) It divert extra neutrons
c) It slow down the speed of fast neutrons
d) It absorb the heat energy caused by nuclear reaction
Answer: d
Explanation: Neutrons rejected during the fission process at a very high velocity of about 1.5 × 107 m/s. For more effective use in nuclear reactor it is desirable to slow down the fast neutrons to speed corresponding to the speed of molecules of gas at normal temperature and pressure. This is accomplished with the help of moderator.
3. Which of the following material is not used as moderator?
a) Oxygen
b) Ordinary water
c) Heavy water
d) Graphite
Answer: a
Explanation: At present the common moderator materials used are graphite, ordinary water and heavy water. Oxygen is not suitable to use due to its low density and the consequent small number of collision.
4. Which of the following part of nuclear reactor is used to control the rate of reaction.
a) Moderator
b) Control rods
c) Reflector
d) Coolant
Answer: b
Explanation: In a reactor the chain reaction is to be maintained at steady value during the operation of reactor. Also the reactor must be able to shutdown automatically under emergency conditions. All these requires control rods for control of reactor so as to prevent the melting of fuel rods, disintegration of coolant and destruction of reactor as the amount of energy released is enormous.
5. Which of the following is the most essential requirement of control rod material?
a) It must be light weight
b) It must be cheap
c) It must have high absorption capacity for neutrons
d) It must be very reflective to neutrons
Answer: c
Explanation: The function of control rod is to control the rate of nuclear reaction by absorption extra release neutrons. Chain reaction is controlled either by removing or inserting neutron absorbing materials. The materials used for control rods must have very high absorption capacity for entrance.
6. Which of the following can be used as both as coolant and moderator ?
a) Helium
b) Molten sodium
c) Lithium
d) Ordinary water
Answer: d
Explanation: A good coolant should not absorb neutrons, should be non-oxidizing, non-toxic, non corrosive, should have high chemical and radiation stability and good heat transfer ability. Ordinary water is used as both as coolant and moderator in boiling water reactor and pressurized water is used as both as coolant and moderator in pressurized water reactor.
7. In thermal reactors control is very easy in comparison to other reactors.
a) True
b) False
Answer: a
Explanation: In thermal reactor control his very easy because of relatively low power densities and longer in neutron lifetime.
8. The main body of reactor is called ____________
a) Thermal shielding
b) Reactor vessel
c) Reflector
d) Biological shielding
Answer: b
Explanation: The reactor core, reflector and thermal shielding are all enclosed in the main body of reactor and is called reactor vessel or tank. It is strong walled container and provides the entrance and exit for the coolant. It also provides the passage for flow of coolant through and around the reactor core.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Classification of Nuclear Reactors”.
1. Reactors used for electricity generation are called ______________
a) Research and development reactors
b) Production reactors
c) Power reactors
d) Electron reactors
Answer: c
Explanation: Power reactors are used for electrical power generation purpose. Research and development reactors are used for testing new reactor design ans research. Production reactors are used for converting fertile material into fissile materials.
2. What is the difference in size of thermal reactor and fast reactor?
a) Size of thermal reactor is slightly more than size of fast reactor
b) Size of thermal reactor is slightly less than size of fast reactor
c) Size of thermal reactor is very much larger than size of fast reactor
d) Both are of same size
Answer: c
Explanation: The moderator to fuel volume ratio for thermal reactor lies between 20 to 80. Same ratio for fast reactor is very less that’s why the size of thermal reactor is very much greater than size of fast reactors.
3. Which of the following reactors does not need moderator?
a) Thermal reactor
b) Fast reactor
c) Intermediate reactor
d) Power reactor
Answer: b
Explanation: In fast reactors fission is caused by fast neutrons, so there is no need of moderator to slow down the neutrons. While in other reactors fission is needed to be from slow or intermediate speed neutrons, so moderator is required to slow down the fast neutrons.
4. Heat energy generated in per unit volume of reactor core in thermal reactor is ___________
a) less than that in fast reactors
b) more than that in fast reactors
c) equal to that and fast reactors
d) unpredictable
Answer: a
Explanation: In fast reactors fission occurs due to fast moving neutrons. Hence, the rate of fission reaction is high and the heat energy generated is also very high. In thermal reactor moderator is used to slow down the neutrons and to make the fission in much more controlled way. So, heat generated in thermal reactor is cocomparatively less.
5. In which of the following reactors material converted into fissile materials is more than fissile material consumed?
a) Burner reactor
b) Slow reactors
c) Converter reactor
d) Breeder reactor
Answer: d
Explanation: Burner reactor or thermal reactor is designed only to consume fissile materials and to give heat energy. Converter reactor converts fertile material into fissile material but the rate of conversion is slower than rate of conception. Only breeder reactor from above options is such a reactor which converts fertile materials into fissile materials faster than consumption of fissile materials.
6. Which of the following reactors uses its fuel as coolant?
a) Direct reactor
b) Indirect reactor
c) Both direct and indirect reactor
d) Solid fuel reactor
Answer: a
Explanation: On the basis of cooling system employed reactors are of two types. One is Direct and another is indirect reactor. Direct reactor used as fuel in liquid form and it acts as coolant. It is circulated through the heat exchanger in which heat is transferred to water to produce steam.
7. Which of the following statement is true?
I. In homogeneous reactors the nuclear fuel and the moderator represents a uniform mixture in the fluid form.
II. In heterogeneous reactors separate fuel sludge or roads are inserted in the moderator
III. Most of the nuclear reactors used these days are of homogeneous type
a) Only statement I and II are true
b) Only statement I and III are true
c) Only statement II and III are true
d) Only statement III is true
Answer: a
Explanation: The statement I and II are true but statement III is wrong, because most of the reactors are of heterogeneous type. i.e.fuel is used in them are separate mostly in form of road fuel rod.
8. In which of the following reactor it is possible to add remove and process the reactor fuel during reactor operation?
a) Homogeneous reactor
b) Heterogeneous reactor
c) Solid fuel reactor
d) Both homogeneous and heterogeneous reactors
Answer: a
Explanation: In homogeneous reactor nuclear fuel and the moderator represent a uniform mixture, in the fluid form including gases liquids and slurries. Due to fluid form of fuel it is possible in homogeneous reactor that reactor fuel can be added removed and reprocessed during reactor operation without shutting in town.
9. In which of the following reactors fissile and fertile materials are kept separate?
a) In one region reactor
b) In two region reactor
c) In one and two region reactor
d) It is impossible to separate them
Answer: b
Explanation: As per arrangement of fertile and fissile materials the reactors are classified into categories. In first category of reactors fertile and fissile fuels are mixed and are called One Region Reactor. In second category of reactors a fertile and fissile material are separate and is called to Region Reactor.
10. Any leakage or component failure in primary nuclear fission reactor coolant system is dangerous.
a) True
b) False
Answer: a
Explanation: Above statement is true because these failures are very much difficult to repair. It is because of the presence of fission products in the coolant which can cause contamination.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Gas Turbine Power Plants & Types of Tariffs”.
1. The installation time for a gas turbine power plant is ______________
a) Comparatively less than thermal power plant
b) Comparatively more than thermal power plant
c) Equal to thermal power plant
d) Very much longer than thermal power plant
Answer: a
Explanation: Gas turbine power plant is comparatively simpler in construction than thermal power plant. So, its installation time is less than a thermal power plant for same capacity.
2. Which of the following is not used in gas turbine power plant?
a) Compressor
b) Turbine
c) Combustion chamber
d) Condenser
Answer: d
Explanation: Natural gas itself or mixture of natural gas and air is used as working medium in gas turbine power plant. Condenser is a device or arrangement used to condense low pressure steam already used by turbine. There is no steam in gas turbine power plant so no condenser is required.
3. Which component of gas turbine power plant is main cause of its low efficiency?
a) Gas turbine
b) Combustion chamber
c) Compressor
d) Starting motor
Answer: c
Explanation: The overall efficiency of gas turbine is low, because a greater part of power developed by the turbine is used in driving the compressor.
4. What is intercooling in gas turbine power plant?
a) Removal of heat from combustion gas between stages of turbine
b) Removal of heat from compressor between stages of compressor
c) Removal of heat from intake air
d) Removal of heat from exhaust air
Answer: b
Explanation: Intercooling means removal of heat from compressed air between low pressure and high pressure compressor. Cooling the low pressure compressed air reduces the air volume and improves the thermal efficiency, air rate and work ratio.
5. What is the function of regenerator?
a) Eatery compresses the exhaust gases
b) It heats the compressed air
c) It regenerates the combustible gas from exhaust gas
d) It regenerates the combustible oil from exhaust gas
Answer: b
Explanation: Regenerator is usually of shell and tube construction. Regenerator uses the heat of exhaust gas to heat compressed air before it is sent to combustion chamber. This reduces the fuel consumption and improves the cycle thermal efficiency.
6. Fuel other than natural gas i.e. solid and liquid fuels can be used in _______
a) open cycle gas turbine power plant
b) closed cycle gas turbine power plant
c) open and closed cycle gas turbine power plant
d) only natural gas is used in gas turbine power plant
Answer: b
Explanation: In closed cycle gas turbine power plant the working medium is heated externally and the fuel is not mixed with working fluid. This ensures the use of any fuel such as inferior type or solid type fuel.
7. Which of the following gas turbine power plant can use working medium of required property?
a) Closed cycle gas turbine power plant
b) Open cycle gas turbine power plant
c) Open and closed cycle gas turbine power plant
d) No gas turbine power plant can use working medium of required property.
Answer: a
Explanation: A working medium with physical properties superior to those of air such as helium and hydrogen can be used in closed cycle gas turbine power plant. This is because of airtight construction of this plant.
8. What is the tariff in case of power system?
a) The taxes which a power plant pay to Indian government
b) The taxes which a power plant pay to state government
c) The taxes which a Power Grid pay to Indian government
d) The schedule of rates are charged of supply of electricity for consumers
Answer: d
Explanation: Tariff means the schedule of rates are charges tariff. In case of electric supply means the schedule of rates framed for supply of electrical energy to different classes of consumer.
9. An electricity supplier is charging for the electricity as per the total load connected, fixed number of hours. This type of tariff will be a ___________
a) Simple tariff
b) Flat demand tariff
c) Flat rate tariff
d) Block rate tariff
Answer: b
Explanation: When the use of Electricity was mainly restricted to very few applications such as for lamps it is ee and the number of hours of use of lamp were fixed they were charged on the basis of total load connected in Kilowatt and the fixed number of hours of use district is known as flat demand tariff.
10. Which statement about simple tariff is true?
a) Charges are made as per the total load connected and of fixed duration of use
b) Charges are made on the basis of units consumed in a certain period
c) Different types of consumers are charged differently
d) Charges per kilowatt decreases with increase in unit consumed
Answer: b
Explanation: In simple tariff cost of energy is charged on the basis of unit consumed cost per KWh is given by summing annual fixed cost and annual operating cost and dividing it by total number of units applied to the consumer per annum.
11. Identify the type of tariff the consumer is charged Rs 4 per unit if the consumer does not exceed 50 KWh, Rs 3.50 per unit if the consumer does not exceed 50 KWh but less than 200 kilowatt hour, and Rs 3 per KWh if consumer exceeds 200 kilowatt hour.
a) Flat demand tariff
b) Simple tariff
c) Flat rate tariff
d) Step rate tariff
Answer: d
Explanation: Step rate tariff is a group of flat rate tariff of decreasing unit charges for higher range of conception. Charges per KWh are reduced for increas in power consumption above different predefined step levels. This type of tariff takes into account the fact of lower generation cost going to higher energy consumption consequent to improvement of load factor.
12. What is demand factor of commercial consumers?
a) Low
b) Low
c) High
d) More than 1
Answer: c
Explanation: Demand factor is the ratio of maximum demand to connected load. As we know maximum demand cannot be greater than connected load so demand factor is always less than one. Commercial consumer generally used as most of disconnected loads so their demand factor is high.
13. If an industrial consumer consumes 50KW for 4 hours, 300KW for 15 hours and 60KW for 5 hours daily and the tariff rate is Rs 5/KWh. What is the energy consumption in a month of 30 days?
a) Rs 750000
b) Rs 475000
c) Rs 755000
d) Rs 470000
Answer: a
Explanation: Energy Consumed in one day = KWh = 5000 KWh
Energy Consumed in one month = 5000× 30
= 150000 KWh
Hence, Charge on one month = 150000 × 5
=750000 Rupees.
14. Monthly consumption of a consumer is 500KWh. What will be the monthly bill at the following rate?
First 100 unit Rs 0.6/KWh
Next 100 units Rs 0.5/KWh
Remaining units Rs 0.4/KWh
a) Rs 250
b) Rs 25
c) Rs 230
d) Rs 23
Answer: c
Explanation: 500 KWh = KWh
Bill for one month consumption
= Rupees
= 230 Rupees.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Conductor Materials”.
1. In stranded conductor of 6 layers, what will be the total number of individual wire?
a) 75
b) 85
c) 84
d) 74
Answer: b
Explanation: Standard conductors usually have the central wire around with there at successive layers of wires. For n layers the number of individual wire is 3n +1. Where ‘n’ is number of layers.
2. A standard conductor have three layers of wire. What will be the diameter of stranded conductor if diameter of each strand is 5 mm?
a) 38 mm
b) 15 mm
c) 20 mm
d) 35 mm
Answer: d
Explanation: If the diameter of each strand is ‘d’ then diameter of the standard conductor will be d. ‘n’ is number of layers.
3. What is the disadvantage of using Stranded Hard Drawn Copper for overhead transmission lines?
a) Low tensile strength
b) Due to electrolytic troubles
c) Corrosion
d) High cost
Answer: d
Explanation: Hard Drawn Copper have good tensile strength, does not corrodes in normal atmosphere and is not subject to electrolytic troubles. Owing to the difficulty of importing copper due to lack of foreign exchange in our country, cost of copper is higher than aluminium. The trend now days is to use aluminium in place of copper.
4. Which of the following conductors are most suitable for short lines supplying rural areas and operating at voltage of about 11 Kv?
a) Hard Drawn Copper Conductor
b) ACSR Conductor
c) Galvanized steel
d) Phosphor Bronze
Answer: c
Explanation: Galvanized steel have great tensile strength and so it can be used for extremely long spans,or for short line section exposed to normally high stresses due to climatic conditions. These conductors are most suitable for lines supplying rural areas and operating at voltages of about 11 Kv where cheapness is the main consideration.
5. Which of the following conductive material will be preferred when harmful gases such as ammonia are present in atmosphere?
a) Cadmium copper
b) Phosphor bronze
c) Galvanized steel
d) Aluminium
Answer: b
Explanation: When harmful gases such as Ammonia are present in atmosphere and the spans are extremely long, phosphor bronze is most suitable material for an overhead line conductor for such situation.
6. What is the amount of Corona losses in ACSR conductors in comparison to copper conductors?
a) Low
b) High
c) Same
d) No Corona loss
Answer: a
Explanation: The ACSR conductors has a largest diameter than any other type of conductor of same resistance, so corona losses are low in ACSR conductors.
7. What is the advantage of cadmium copper over hard drawn copper?
a) Higher conductivity
b) Higher tensile strength
c) Low cost
d) Low conductivity
Answer: b
Explanation: Addition of 1 or 2% of cadmium in copper increases the tensile strength by about 40% and reduces the conductivity only by 17% below that of pure copper. However, cadmium copper is costlier than pure copper, its use will be economical for a line with long spans and small cross section.
8. In extra High Voltage lines, which conductor material is used for ground wire provided above the line conductors for protection against lightning?
a) Hard drawn copper
b) Cadmium copper
c) Stranded galvanized steel
d) ACSR
Answer: c
Explanation: Due to very poor conductivity, about 30% of copper and higher eddy current and hysteresis losses. Application of galvanized steel wire is limited to telecommunication lines stay wire Earth wire and guard wires. Stranded galvanized steel wires are used as guy wires and earth wires.
9. Which of the following conductor is needed to use with shortest span?
a) ACSR Conductors
b) All Aluminium Conductors
c) Hard Drawn Copper Conductors
d) Cadmium Copper Conductors
Answer: b
Explanation: All aluminium conductors have low tensile strength. Linear coefficient of expansion of Aluminium is 1.4 times that of copper and so sag is greater in aluminium wires. Due to these characteristics, aluminium stranded conductors are mainly used for low voltage distribution overhead lines having shorts spans of up to 65 m.
10. Which of the following wire is used as stay wire?
a) All Aluminium Conductors
b) Standard Galvanized Steel Conductors
c) Cadmium Copper Conductors
d) Phosphor Bronze Conductors
Answer: b
Explanation: Stay wires are used for supporting poles and towers. Standard galvanized steel conductors have great tensile strength and superior mechanical properties. So standard galvanized steel wires are widely used as stay wire and earth wire.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Sag and Tension, Vibrations and Dampers”.
1. What happens to the tension in a conductor hanged between two poles, when temperature varies?
a) Tension increases with increase in temperature
b) Tension decreases with increase in temperature
c) Tension first increases and decreases with decrease in temperature
d) Tension in conductor is independent of temperature variation
Answer: b
Explanation: The relationship between tension and sag is dependent on the loading conditions and temperature variations. For instance, the tension increases when temperature decreases.
2. What is the effect of rise in temperature on sag when Ice and wind effect are eliminated?
a) Sag decreases
b) Sag increases
c) Sag remains constant
d) Sag becomes zero
Answer: b
Explanation: All metallic body expand with rise in temperature and therefore the length of the conductor increases with the rise in temperature and so does Sag.
3. What is the relation between length of span and sag?
a) sag ∝ √span
b) sag ∝
c) sac ∝ span 2
d) Sagar ∝ span 3
Answer: c
Explanation: Ultimate stress is directly proportional to the square of span length. Other conditions such as type of conductor working tension temperature it is it remains the same affection with longest and we’ll have much greater Sag.
4. What should be the value of sag for proper operation of overhead transmission line?
a) High
b) Low
c) Nither too low nor too high
d) Anything
Answer: c
Explanation: If the sag is too high more conductor material is required resulting more weight on the supports. If the sag is too low, there is more tension in the conductor and thus it is liable to break if any additional stress such as due to vibrations or due to fall in temperature occurs.
5. An overhead transmission line has a span of 220 metres the conductor waiting 0.604 kg/m. What will be the maximum sag if the working tension is 2879 kg.
a) 8.96 m
b) 8.86 m
c) 8.85 m
d) 1.27 m
Answer: d
Explanation:
S = ωL 2 /8T
Where ,
ω – weight of conductor per meter
L – span
T – Working tension
Therefore, S = /
= 1.269 m ~ 1.27 m.
6. What is the value of working stress in overhead conductors?
a) Less than ultimate stress
b) More than ultimate stress
c) Always equal to ultimate stress
d) Should be zero
Answer: a
Explanation: Working tensile strength of the conductor is determined by multiplying the ultimate stress and area of cross section and dividing by a factor of safety. Due to division of ultimate stress by factor of safety the value of working stress is always less than value of ultimate stress.
7. When the sag exceeds 10% of the span length, the shape made by the conductor is similar to which of the following shape?
a) Hyperbola
b) Parabola
c) Catenary
d) Straight line
Answer: c
Explanation: A flexible wire of uniform cross section when string between two suppose at the same level will form a category however if the sag is very small as well as less than 10% of the span length then its shape approximates a parabola.
8. What will be the resultant weight on per meter of length of conductor if weight of conductor is 150 kg/m, weight of ice in per meter of length is 60 kg/m and wind force is 200 Kg/m.?
a) 300 kg/m
b) 468 kg/m
c) 290 kg/m
d) 390 Kg/m
Answer: c
Explanation:
Resultant stress = √[{(w c + w i )2 + w w 2 }] = √[{ 2 + 200 2 }] = 290 kg.
9. What are aeoline vibrations in overhead transmission line conductors?
a) High frequency and low amplitude vibrations
b) High frequency and high amplitude vibrations
c) Low frequency and low amplitude vibrations
d) Low frequency and high amplitude vibrations
Answer: a
Explanation: Aeoline vibrations are high frequency and low amplitude vibrations. They are caused by vortex phenomenon in light winds .
10. What are galloping vibrations in overhead transmission line conductors?
a) High frequency and low amplitude vibrations
b) High frequency and high amplitude vibrations
c) Low frequency and low amplitude vibrations
d) Low frequency and high amplitude vibrations
Answer: d
Explanation: Galloping vibrations in overhead transmission lines are low friquency and high amplitude vibrations. They occurs during sleet storms with a strong winds. In such situations conductors are said to ‘dance’.
11. Which of the following vibrations causes different conductors to touch due to high swing?
a) Aeoline vibrations
b) Galloping vibrations
c) Aeoline and Galloping
d) Amplitude vibrations
Answer: b
Explanation: Galloping vibrations in overhead transmission lines are high amplitude vibrations. During such vibrations conductors ‘dance’ in horizontal and vertical directions with high amplitude which makes the conductors to touch each other.
12. ‘Dancing’ of overhead conductors occurs during which of the following types of vibrations?
a) Aeoline vibrations
b) Galloping vibrations
c) Aeoline and Galloping
d) Amplitude vibrations
Answer: b
Explanation: During galloping vibrations in overhead transmission lines conductors vibrates with high amplitude and low friquency . Swinging of conductors with high amplitudes in horizontal and vertical directions are called as they are ‘dancing’.
13. What are the method for prevention of low frequency high amplitude vibrations?
a) Horizontal conductor configuration
b) Vertical conductor configuration
c) Horizontal and Vertical conductor configuration
d) There is no method for prevention of such vibrations
Answer: d
Explanation: Horizontal conductor configuration can be used to reduce the danger of low frequency vibrations. But no method can prevent such vibrations.
14. What are the methods used to protect conductors against high frequency resonant vibrations?
a) Horizontal conductor configuration
b) Vertical conductor configuration
c) By using dampers
d) There is no method for prevention of such vibrations
Answer: c
Explanation: The conductors are protected by dampers. Dampers prevents the resonant vibrations from reaching the conductors at the clamps or supports.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Merits of Combined Operation of Power Plants”.
1. Which of the following power plant are put on load for maximum time?
a) Plant with minimum operating cost
b) Plant with medium operating cost
c) Plant with maximum operating cost
d) Operating cost does not matter
Answer: a
Explanation: The power plants with minimum operating cost are put on load for maximum time. Plants with medium operating cost are only loaded when required by the load demand on the system. Plants with maximum operating cost are kept in reserve and would operate only in emergency.
2. Which of the following power plants can be profitably employed for supplying base loads as well as peak loads?
a) Thermal power plant
b) Nuclear power plant
c) Hydroelectric power plant
d) Diesel power plant
Answer: c
Explanation: Seam and Nuclear power plants are only used to supply base load. Diesel power plants are suitable for only peak load. Only hydroelectric power plant can supply both peak load as well as base load because of its flexibility in operation and low operating cost.
3. Plants with higher operating cost and greater flexibility are suitable for?
a) Only Base load
b) Only Peak load
c) Base and Peak loads
d) Plants with higher operating cost are not used
Answer: b
Explanation: Plants which can meet sudden variation of load demand are said to have higher flexibility. Plants with higher operating cost can’t be used as base load plants. Plants with such capabilities are most suitable for peak load plants as they can respond immediately.
4. Plants with maximum operating costs are put on load for :
a) Maximum time
b) During peak load
c) Emergency conditions
d) During Medium loads
Answer: c
Explanation: Power plants with minimum operating cost are put on load for maximum time. Plants with medium operating cost are only loaded when required by the load demand on the system. Plants with maximum operating cost are kept in reserve and would operate only in emergency.
5. Gas turbine power plants are most suitable for which of the following loads?
a) Only Base load
b) Only Peak load
c) Base and Peak loads
d) Gas turbine power plants are not practical
Answer: b
Explanation: Gas turbine power plants have advantage of low initial cost and low startup time. So, it is ideally suited for supplying peak loads.
6. A power system will have greater flexibility of operation if they have __________
a) Various types of power plants operating in combination
b) Only Base load plants operating in combination
c) Only Peak load plants operating in combination
d) Only thermal power plants operating in combination
Answer: a
Explanation: If various types of power plants are operated in combination, the system will become more flexible i.e Steam and Nuclear power plants will supply base loads, Hydroelectric power plants will supply base or peak loads depending upon the availability of water, Gas turbine power plant will meet peak load demand and existing Diesel power plant will operate in emergency only.
7. Which of the following system is more reliable?
a) Hydroelectric power plant
b) Steam power plant
c) Combined operating steam and hydroelectric power plant
d) Diesel power plant
Answer: c
Explanation: The reliability of steam power plant depends upon the coal supply, that of hydroelectric power plant on stream flow. Due to greater diversity a combine operation of various types of power plant would be more reliable than individual steam or hydro power plant.
8. In combined operation of several power plants the reserve capacity requirement is reduced.
a) True
b) False
Answer: a
Explanation: In any electric power system the system has to have a certain reserve capacity in order to meet any unforeseen excess power demand. In combined system the effect of all the diversity is may result in still larger benefit from the point of view of Reserve capacity.
9. Thermal power plants are not suitable for supplying base peak loads.
a) True
b) False
Answer: a
Explanation: To operate as peak load plant, a power plant must be able to meet sudden variation of load. The major drawback of a steam power plant is that it requires appreciable time to start up, synchronize and take up load. Hence thermal power plant is not suitable to work as peak load plant.
10. Read the following statements:
I. Diesel power plant is generally used as base load plant.
II. Gas turbine power plant is used as peak load plant.
a) Only I is correct
b) Only II is correct
c) I and II are correct
d) I and II are wrong
Answer: b
Explanation: To supply base load the operation cost should be minimum, but Diesel power plant has very high operating cost. Diesel power plants are best suitable to supply peak loads. Gas turbine can be started in less time and so it is suitable to supply peak loads.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Base Load and Peak Load”.
1. The unvarying load, which occurs almost the whole day on the power plant is called _________
a) Base load
b) Peak load
c) Average load
d) Discrete load
Answer: a
Explanation: The load on any power plant can be conveniently considered into two parts namely ‘base load’ and ‘peak load’. The unvarying load which occurs almost the whole day on the power plant is called base load.
2. If there is one power plant only, the installed capacity of that power plant should be equal to ____
a) Average load
b) Base load
c) Peak load
d) Minimum load
Answer: c
Explanation: If the load is to be supplied from one power plant only then the installed capacity of the plant should be equal to the peak load or more. Otherwise during peak load period the plant will not be able to meet the load demand.
3. The various peak demands of the load above the base load of power plant is called _________
a) Base load
b) Over load
c) Extra load
d) Peak load
Answer: d
Explanation: Various peak demands of the load over and above the base load of the power plant is called peak load. The unvarying load which occurs almost the whole day on the power plant is called base load.
4. The system supplying base and peak loads will be more economical if power is supplied by _________
a) Only gas turbine power plant
b) Only thermal power plant
c) Only Deasel power plant
d) Combined operation of various power plants.
Answer: d
Explanation: The system containing only one power plant would be uneconomical since. Gas turbine and Diesel power plants operate economically only for peak load and Thermal power plant is suitable only for base load. Hence such power loads should not be supplied from single power plant.
5. Power plants to be employed as base load plants are not required to have ___________
a) Capability of working continuously
b) Low operating cost
c) Capability of quick start
d) Economical and speedy repair
Answer: c
Explanation: Capability of quick start is the essential requirement for peak load plant. Base load plants are started once and operated for long time so capability of quick start is not an essential requirement for base load plants.
6. Which of the following is an essential requirement for a peak load plant ___________
a) Capability of working continuously
b) Low operating cost
c) Capability of quick start
d) Economical and speedy repair
Answer: c
Explanation: The power plants to be employed as peak load plant should only have the capability of quick start, synchronization and taking up of system load and quick response to load variations.
7. Which of the following is not suitable to uses as peak plant?
a) Hydroelectric power plant
b) Gas power plant
c) Diesel elected plant
d) Nuclear power plant
Answer: d
Explanation: The power plants to be employed as peak load plant should have the capability of quick start and quick response to load variations. Nuclear power plant is not suitable for variable load operation as the reactor cannot be easily controlled to respond quickly to load variations.
8. Which of the following power plant cannot be used as base load plant?
a) Hydroelectric power plant
b) Nuclear power plant
c) Diesel elected plant
d) Thermal power plant
Answer: c
Explanation: The power plant to be employed as base load plant should have low operating cost. Diesel power plants have very high operating cost and so it is not suitable to use as base load plant.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Air Pollution”.
1. Which of the following power plant causes highest amount of air pollution?
a) Thermal power plant
b) Hydroelectric power plant
c) Nuclear power plant
d) Geothermal power plant
Answer: a
Explanation: The major contribution of electrical power generation is from thermal power plant. The thermal power plant definitely contribute to economic growth but they bring with it like air and water pollution. Thermal power plant mostly causes air pollution by the emission of flue gases into air.
2. Which of the following gas is not emitted during combustion of coal?
a) Oxides of sulphur
b) Oxides of Nitrogen
c) Oxides of Mercury
d) Oxides of carbon
Answer: c
Explanation: Thermal power plant emit large amount of harmful gases such a Sulphur dioxide, nitrogen oxide, CO, CO 2 , certain hydrocarbons and particulates during the combustion of fossil fuels. There is no any emission of oxides of mercury.
3. Which of the following pollutants emitted by thermal power plant causes irritation in Eyes?
a) Oxides of sulphur
b) Oxides of Nitrogen
c) Oxides of Mercury
d) Oxides of carbon
Answer: b
Explanation: At high temperatures existing in the flame core of high power boilers, the nitrogen of fuel and air may partially be oxidised to form nitrogen oxides. These are toxic and produce a sharp irritating effect especially on the mucous membrane of the eye.
4. Which of the following pollutants emitted by thermal power plant is a cause of global warming?
a) NO
b) CO 2
c) SO 2
d) NO 2
Answer: b
Explanation: Carbon monoxide and carbon dioxide are also emitted during the combustion of coal. Carbon monoxide is very toxic pollutant but it gets converted into carbon dioxide in open atmosphere surrounding the power station. On the other hand carbon dioxide has been identified as major cause of global warming.
5. Which of the following pollutant causes acid rain?
a) NO
b) CO 2
c) SO 2
d) NO 2
Answer: c
Explanation: The Sulphur Dioxide emitted by thermal power plant gradually oxides to sulphur trioxide under the influence of Sunlight. This in turn interact with atmospheric moisture and forms sulphuric acid. This sulphuric acid later causes acid rain.
6. Which of the following is mostly affected by thermal power plant pollutants?
a) Lithosphere
b) Atmosphere
c) Hydrosphere
d) Exosphere
Answer: b
Explanation: The thermal power plant mostly causes air pollution by the emission of harmful flue gases. So, it can be said that thermal power plant mostly pollutes our atmosphere.
7. Hydroelectric power plants with limited storage are suitable to supply __________
a) Base load
b) Peak load
c) Base load and Peak load
d) Average load
Answer: c
Explanation: The hydropower plant should be employed for supplying base load. But hydro power plants with limited water storage cannot supply base load. Hence they are suitable for peak loads.
8. Nuclear power plants are suitable only for load factor over _________
a) 0.5
b) 0.7
c) 0.3
d) 0.8
Answer: d
Explanation: Nuclear power plant is not suitable for variable load operation as the reactor cannot be easily controlled to respond quickly to load variations. Such a plant is used as base load plant only operating at high load factors of over 0.8.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Cost Analysis of Power Plants”.
1. Which of the following costs come under semi fixed cost?
a) Salaries of high officials
b) Salaries of operational and maintenance staff
c) Salaries of Management and clerical staff
d) Annual cost of fuel
Answer: c
Explanation: The semi fixed cost is due to annual interest, the capital cost of generating plant transmission and distribution network building and other civil works, all types of taxes and insurance charges and salaries of Management and clerical staff. Salaries of higher officer is a fixed cost and salaries of operation and maintenance staff is running or operating cost.
2. Which power plant has minimum operating cost?
a) Hydroelectric power plant
b) Thermal power plant
c) Nuclear power plant
d) Gas Turbine Power Plant
Answer: a
Explanation: Hydroelectric power plant has lowest running cost because it does not needs any fuel and can be operated by few number of persons. Nuclear gas and thermal power plant requires fuels also the handling cost of fuels is added with the total cost.
3. Which of the following is most likely to nuclear power plant?
a) Thermal power plant
b) Hydroelectric power plant
c) Gas turbine power plant
d) Nuclear power plant
Answer: d
Explanation: Most of the parts of nuclear power plants are similar to the thermal power plant, except the heat generating system. In thermal power plant heat energy is produced by the combustion of fossil fuels like coal, Oil or gas. In nuclear power plant the heat energy is produced by Nuclear Fission of nuclear fuels like Uranium or plutonium in reactor.
4. Which of the following have highest operating cost?
a) Hydroelectric power plant
b) Thermal power plant
c) Nuclear power plant
d) Solar electric power plant
Answer: b
Explanation: Operating cost of hydroelectric and Solar Power Plant are very low because they don’t need fuel. In nuclear power plant fuel required is of very small quantity as compared to coal required by thermal power plant. Due to above the cost of transportation of fuel and also the cost of fuel itself is low for nuclear power plant.
5. Which of the following least affect the cost of electricity produced in thermal power plant?
a) Cost of fuel
b) Cost of transportation
c) The load factor
d) Salaries of higher officials
Answer: d
Explanation: Change in fuel cost by 20% main cause about 8% variation in total cost per KWh generated. Cost of transportation and the load factor changes and also cause variation in fuel cost. The salaries of higher officials comes under fixed cost and so it does not affects the cost of fuel.
6. Which of the following power plant have longest physical life?
a) Thermal power plant
b) Nuclear power plant
c) Hydroelectric power plant
d) Diesel power plant
Answer: c
Explanation: Thermal and diesel power plants are so constructed that their efficiency Falls over time faster as compared to hydroelectric power plant. Nuclear power plant also needs maintenance over time. The components of hydroelectric power plant including turbine, generator and the concrete Dam are so rugged in construction that their life maybe as long as 80 years or even longer.
7. When load factor and diversity factor increases ___________
a) cost of electricity decreases
b) cost of electricity also increases
c) cost of electricity remains same
d) cost of electricity increases exponential
Answer: a
Explanation: Load factor and diversity factor playes an important role in cost of supply of electrical energy. Higher the value of load factor and diversity factor, lower will be the cost per unit generated.
8. Which of the following has highest diversity factor?
a) Domestic lightning
b) Commercial lightning
c) Industrial power
d) Domestic power
Answer: a
Explanation: Diversity fector of all of the options rangers from 1.5 to 2. The diversity factor of domestic lightning upto 1 kilo watt rangers from 3 to 5.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Economics of Power Generation”.
1. What is the advantage of sectionalizing of power plant?
a) High reliability
b) Low capital cost
c) Low maintenance
d) Easy operation
Answer: a
Explanation: Sectionalizing means installing more number of small units rather than installing a big unit. Doing so enables us to maintain continuity of supply from rest of the units, when one or two units of plant fails. this makes the plant more reliable.
2. The area under the load curve represents ____________
a) the average load on power system
b) maximum demand
c) number of units generated
d) load factor
Answer: c
Explanation: Load curve is obtained by plotting fluctuating load be keeping load on y axis and time in x axis. The area under the load curve represents the total number of units generated in a particular time.
3. Which of the following is equal to the maximum demand?
a) The ratio of area under curve to the total area of rectangle
b) The ratio of area under curve and number of hours
c) The peak of the load curve
d) The area under the curve
Answer: c
Explanation: The ratio of area under curve to the total area of the rectangle is called load factor. The ratio of area under the curve to the number of hours represents the average load. The peak of the curve represents the maximum demand.
4. Load duration curve indicates _______
a) the variation of load during different hours of the day
b) total number of units generated for the given demand
c) total energy consumed by the load
d) the number of hours for which the particular load lasts during a day
Answer: d
Explanation: The variation of load during different hours of the day is shown by load curve. Load duration curve is different from Load curve. Load duration curve indicates the variation of the load, but with the load arranged in descending order of magnitude. Load duration curve give the number of hours for which a particular load lasts during a day.
5. During which time the demand of electrical energy is maximum?
a) 2 A.M. to 5 A.M.
b) 5 A.M. to 12 P.M.
c) 12 P.M. to 7 P.M.
d) 7 P.M. to 9 P.M
Answer: d
Explanation: From the load curve it is obtained that during early morning demand is always low. Around 5 A.M. it starts increasing and around 9 A.M. load reaches a high value and remains almost constant till evening except for some Dip during lunch hours. The load again starts increasing in evening hours and reaches its peak around 7 to 9 P.M.
6. Size and cost of installation depends upon ____________
a) average load
b) maximum demand
c) square mean load
d) square of peak load
Answer: b
Explanation: The greatest of all “short time interval averaged” during a given period, on the power system is called the maximum demand. Maximum demand represents the maximum amount of load that is active, out of total connected load. So the size and rating of power plant depends on Maximum demand.
7. What is Demand factor?
a) Ratio of connected load to maximum demand
b) Ratio of average load to connected load
c) Ratio of maximum demand to the connected load
d) Ratio of kilowatt hour consumed to 24 hours
Answer: c
Explanation: Demand factor is the ratio of actual maximum demand on the system to the total load connected to the system. The idea of demand factor was introduced due to the fact that all the equipments connected to the system does not work at a time in practice.
8. Which of the following represents the annual average load?
a) /24
b) {/ 24 } × 365
c) {/
d) /
Answer: d
Explanation: The average load on the power station is average of load occurring at the various events. It can also be stated as energy deliver in a given period divided by the number of hours in that period. Option d matches correctly to these statements.
9. The load factor is __________
a) always less than unity
b) less than or greater than 1
c) always greater than 1
d) less than zero
Answer: a
Explanation: Load factor is the ratio of average demand to the maximum demand. Average demand can not be greater than maximum demand. So the value of load factor is always less than unity.
10. In practice what is the value of diversity factor?
a) Less than Unity
b) Geater than Unity
c) Equal to or greater than Unity
d) Less than zero
Answer: b
Explanation: Maximum demand of different consumers never occurs at a time, due to this the total maximum demand of the load is always less than sum of individual maximum demands. And hence, demand factor e.i. the ratio of sum of individual maximum demand to the maximum demand of total load is always greater than unity.
11. Coincidence factor is reciprocal of ___________
a) average load
b) demand factor
c) capacity factor
d) diversity factor
Answer: d
Explanation: Coincidence factor is the ratio of total maximum demand to the sum of individual maximum demands which is the reciprocal of diversity factor.
12. Which of the following is called as cold reserve?
a) Reserve capacity available but not ready for use
b) Reserve capacity available and ready for use
c) Generating capacity connected to bus and ready to take load
d) Capacity in service in excess of peak load
Answer: a
Explanation: Cold reserve is the generating capacity which is available for service but not normally ready for immediate loading. Reserved capacity available and ready to use are called hot reserve.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Flux Linkages of an Isolated Current-Carrying Conductor”.
1. A 500 MW, 21 kV, 50 Hz three phase two pole alternator has 0.8 lagging p.f. with moment of inertia of 27.5×10 3 kgm -2 . The inertia constant H will be _______ MJ/MVA.
a) 2.17
b) 4.2
c) 2.82
d) 2.62
Answer: a
power-systems-questions-answers-flux-linkage-current-carrying-conductor-q1
2. If the power system network is at Vs∠δ and receiving end voltage is Vr∠0 consisting of the impedance of TL as Ω. For maximum power transfer to the load, the most appropriate value of resistance R should be __________
a) 1.732
b) 3
c) 1.2
d) 0.33
Answer: a
Explanation: For maximum power transfer, X=√3 R
3=√3 R
R=√3.
3. At a 33kV 50 Hz to a bus a load of 35 MW is connected. To improve the power factor to unity a synchronous phase modifier is connected taking 5 MW. If the SPM is represented as delta connected impedance, where in each phase we have capacitor connected parallel to resistance forming RC parallel network, then the value of this resistance is ___________
a) 653.4 Ω
b) 753.6 Ω
c) 280.4 Ω
d) 682 Ω
Answer: a
Explanation: Reactive power fed by SPM = 35tan36.87 = 26.25 MVAR
Active power consumed by prime mover = 5 MW
5*10 6 = 3V 2 /R
R=3 2 /(5*10 6 ) = 653.4 Ω.
4. At a 33kV 50 Hz to a bus a load of 35 MW is connected. To improve the power factor to unity a synchronous phase modifier is connected taking 5 MW. If the SPM is represented as delta connected impedance, where in each phase we have capacitor connected parallel to resistance forming RC parallel network, then the value of this capacitance is __________
a) 25.57 μF
b) 76.2 μF
c) 32.2 μF
d) 24 μF
Answer: a
Explanation: Q=3V 2 Cω
C= 25.57 μF.
5.The transmission efficiency for a single phase line can be expressed as ____________
power-systems-questions-answers-flux-linkage-current-carrying-conductor-q5
Answer: a
Explanation: The efficiency of single phase is
power-systems-questions-answers-flux-linkage-current-carrying-conductor-q5-exp
6. The transmission efficiency for a three phase line can be expressed as _________
power-systems-questions-answers-flux-linkage-current-carrying-conductor-q6
Answer: a
Explanation: The efficiency of three phase system is power-systems-questions-answers-flux-linkage-current-carrying-conductor-q6-exp
7. If the flux linkages are varied sinusoid with current, then what can be concluded about the inductance?
a) Constant
b) Varying with the current
c) Linearly varying
d) Exponential change
Answer: b
Explanation: Inductance = flux linkages/current.
8.The principle behind the influence of the power lines on the telephone lines is __________
a) Faraday’s laws
b) Mutual inductance
c) Self inductance
d) All of the mentioned
Answer: a
Explanation: The concept of mutual inductance is the main reason for the interference between telephone lines and the power lines.
9. The magnetic flux intensity due to the current flowing inside the conductor is _________
power-systems-questions-answers-flux-linkage-current-carrying-conductor-q9-diagram
power-systems-questions-answers-flux-linkage-current-carrying-conductor-q9-options
Answer: a
Explanation: Referring the ampere’s Law,
2πyH=Iy
Assuming uniform current density,
power-systems-questions-answers-flux-linkage-current-carrying-conductor-q10
10. The flux density B, y meters from the centre of conductors in the following diagram, is _______
power-systems-questions-answers-flux-linkage-current-carrying-conductor-q10-1
Answer: a
Explanation: Referring the ampere’s Law,
2πyH=Iy
Assuming uniform current density,
power-systems-questions-answers-flux-linkage-current-carrying-conductor-q10-exp-1
11.The internal flux linking the single infinite conductor causes the inductance of ___________
a) 0.5 *10 -7 H/m
b) 2 *10 -7 H/m
c) 0.5 *10 -7 ln H/m
d) 2 *10 -6 H/m
Answer: a
Explanation: λint = I/2 x 10 -7 Wb-T/m
L= λint/I = 0.5 *10 -7 H/m.
12. The inductance of the conductor contributed by the flux between the point D outside at the distance d from conductor is _____________
a) 0.461 log mH/km
b) 0.4 log mH/km
c) 0.461 log mH/km
d) 0.461 log H/km
Answer: a
Explanation: L= 0.461 log mH/km.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Inductance of a Single-Phase Two-Wire Line – 1”.
1. Effect of earth is considered insignificant while calculating the inductance of a single phase transmission line.
a) True
b) False
Answer: a
Explanation: The earth’s magnetic symmetry does not affect the inductance of the line.
2. Effect of earth’s presence on the magnetic field geometry is _________________
a) significant
b) insignificant
c) cannot be said
d) none of the mentioned
Answer: a
Explanation: This is because the relative permeability of earth is about the same as that of air and its electrical conductivity is relatively small.
3. The inductance of the transmission line is do not contain effect of earth electric field geometry while the capacitances contain.
a) True
b) False
Answer: a
Explanation: It is true as the earth’s magnetic field symmetry is insignificant to the inductance while the electric field symmetry is.
4. The end effect information is included in the inductance of a transmission line.
a) True
b) False
Answer: b
Explanation: Since TL is infinitely long, the end effects are ignored and they are not a part of the inductance formula.
5. The number of the strands included in the stranded cables while implementing a similar cable equivalent of single strand should be ________
a) 3x 2 -3x+1
b) 2x 2 -3x+1
c) 3x 2 -2x+1
d) 3x 2 -x+1
Answer: a
Explanation: It is 3x 2 -3x+1.
6. The overall diameter of a stranded conductor if ‘x’ is the number of layers and each layer has a diameter ‘d’ will be
a) d
b) d
c) d
d) d
Answer: a
Explanation: It is given by d.
7. _______ conductors are the latest trend of the extra high voltage lines.
a) Bundled
b) Parallel
c) ACSR
d) Bundled or ACSR
Answer: a
Explanation: The bundled ACSR conductors have corona free characteristics and they have good tensile strength.
8. A 10 MVA, 11 kV alternator has positive, negative and zero sequence reactance of 25%, 40%,10% respectively. The resistance that must be placed in the neutral such that zero sequence of fault current for a single phase to ground fault will not exceed the rated line current in ohms is
a) 2.66 Ω
b) 1.66 Ω
c) 12.1 Ω
d) 0.22 Ω
Answer: a
Explanation:
power-systems-questions-answers-inductance-single-phase-two-wire-line-1-q8
This set of Power Systems Interview Questions and Answers focuses on “Inductance of a Single-Phase Two-Wire Line – 2”.
1. A 10 MVA, 11 kV alternators has positive, negative and zero sequence reactance of 25%, 40%, 10% respectively. The resistance that must be placed in the neutral such that zero sequence of fault current for a single phase to ground fault will not exceed the rated line current in pu is ______
a) 0.22
b) 0.11
c) 0.16
d) 0.97
Answer: a
Explanation: power-systems-interview-questions-answers-q1
2. A 10 MVA, 11 kV alternator has positive, negative and zero sequence reactance of 25%, 40%, 10% respectively. The resistance that must be placed in the neutral such that fault current for a single phase to ground fault will not exceed the rated line current in pu is _____________
a) 0.97
b) 0.22
c) 0.87
d) 0.45
Answer: a
Explanation:
power-systems-questions-answers-inductance-single-phase-two-wire-line-2-q2
3. A 10 MVA, 11 kV alternator has positive, negative and zero sequence reactance of 25%, 40%, 10% respectively. The resistance that must be placed in the neutral such that fault current for a single phase to ground fault will not exceed the rated line current in ohms is __________
a) 11.7
b) 12.8
c) 2.66
d) 5.2
Answer: a
Explanation:
power-systems-questions-answers-inductance-single-phase-two-wire-line-2-q3
4. Unsymmetrical spacing configurations cause the line interference.
Unsymmetrical spacing causes the voltage induction in the communication lines.
a) and are valid
b) Only is valid
c) Only is valid
d) Both are invalid
Answer: a
Explanation: Both the statements are correct as the unsymmetrical spacing causes the unbalanced voltage generation.
5. Unsymmetrical spacing configurations cause the line interference.
Unsymmetrical spacing causes the voltage induction in the communication lines.
The above problems can be eliminated by ________
a) transposition
b) parallel lines
c) three phase
d) all of the mentioned
Answer: a
Explanation: Transposition meaning exchange of conductors will cause the net voltage induced in the other lines to be zero as the net inductance remains constant.
6.Transposition is the mean to balance ____________
a) Inductance
b) Voltage
c) Current
d) All of the mentioned
Answer: a
Explanation: Transposition primarily balances the inductances in the line thus causing a constant inductance throughout the line.
7. Over the length of one transposition cycle of a power line, the total flux linkages of a nearby telephone line are zero for the unbalanced three phase currents.
a) True
b) False
Answer: b
Explanation: For an unbalanced supply, there will be non zero flux zero flux linkages in the telephone lines.
8. Over the length of one transposition cycle of a power line, the total flux linkages of a nearby telephone line are zero for the balanced three phase currents.
a) The above statement is valid
b) The above statement is invalid
c) It can’t be concluded
d) The above statement is valid for all conditions.
Answer: a
Explanation: Its valid only with balanced systems.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Inductance of One Conductor in a Group”.
1. Bundled conductors used in the EHV transmission lines result into __________
a) reduced inductance
b) increase capacitance
c) increase inductance
d) increase resistance
Answer: a
Explanation: Bundled conductors cause the GMR to increase and thus reducing the inductance.
2. The fictitious resistance, “ r’ ” implemented in the conductors for the calculation of the inductance is _____________
a) 0.7788r
b) 2r
c) r/0.7788
d) r
Answer: a
Explanation: It is 0.7788r in the equivalent network configuration.
3. Skin effect
Proximity effect
Which of the options are right?
a) Both and cause non uniform distribution of the current
b) Neither and cause non uniform distribution of the current
c) Both and cause uniform distribution of the current
d) Only causes the non uniformity of the current
Answer: a
Explanation: Skin-effect as well as the Proximity effect cause the non distribution of the flux linkages, leading to non uniform distribution of the current.
4. Ferranti effect causes the non uniform distribution of the current and voltage.
a) True
b) False
Answer: b
Explanation: Only the voltage regulation is affected due to the Ferranti law.
5. Apart from the skin effect the phenomena which cause/s the non uniform distribution of the current is ____________
a) Proximity effect
b) Faraday’s effect
c) Ferranti effect
d) All of the mentioned
Answer: a
Explanation: Only the proximity effect and skin effect cause the non uniform distribution of the current.
6. Bundle conductor ______ inductance and ______ capacitance of a transmission line.
a) reduces, increases
b) increases, reduces
c) reduces, keeps constant
d) keeps constant, increases
Answer: a
Explanation: The inductance reduces by employing the bundle conductor.
7. For a transmission line, the distributed parameters is/are ____________
a) Resistance, inductance, capacitance
b) Resistance
c) Inductance, capacitance
d) None of the mentioned
Answer: a
Explanation: All R, L and C are considered distributed parameters.
8. As the frequency increases, the flux inside the conductor will ________
a) decrease
b) increase
c) be constant
d) be zero
Answer: a
Explanation: Skin effect is inversely proportional to frequency.
9. Self GMD and GMR vary with each other as __________
a) linearly
b) parabolic
c) exponential
d) none of the mentioned
Answer: d
Explanation: Because the self GMD and GMR are same quantities.
10. If the diameter of the conductor is increased then _____________
a) inductance increases
b) inductance remains unaltered
c) inductance decreases
d) inductance can’s be determined
Answer: a
Explanation: Inductance will increase.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Inductance of Composite Conductor Lines – 1”.
1. Consider the figure as shown below:-
power-systems-questions-answers-inductance-composite-conductor-line-1-q1
The line capacitance will be given by __________________
power-systems-questions-answers-inductance-composite-conductor-line-1-q1-options
Answer: a
Explanation: For the given configuration,
power-systems-questions-answers-inductance-composite-conductor-line-1-q1-exp
2. Consider the figure as shown below:-
power-systems-questions-answers-inductance-composite-conductor-line-1-q2
The phase capacitance will be given by ____________
power-systems-questions-answers-inductance-composite-conductor-line-1-q2-options
Answer: b
Explanation: For the given configuration,
power-systems-questions-answers-inductance-composite-conductor-line-1-q2-options-1
3. The per unit value of any quantity is usually given by _____________
a) /
b) /
c) The actual value in any units* The actual value in any units
d) 1/
Answer: a
Explanation: The per unit value is given as /.
4. If X a is the armature reactance of a synchronous machine and Xl is the leakage reactance of the same machine, then the synchronous reactance is ____________
a) X a +X l
b) ½(X a )
c) 1/2(X a +X l )
d) None of the mentioned
Answer: a
Explanation: X s = X a +X l
5. A large bus system whose voltage and frequency remain constant independent of the power exchange between the synchronous machine and the bus is called ________________
a) infinite bus
b) load bus
c) generator bus
d) cannot be determined
Answer: a
Explanation: It is infinite bus.
6. The power delivered by a synchronous generator to an infinite bus is given by ______
power-systems-questions-answers-inductance-composite-conductor-line-1-q6
Answer: a
Explanation: power-systems-questions-answers-inductance-composite-conductor-line-1-q6-exp
7. In a three phase system the three-phase fault MVA is always higher than the LG fault MVA at a bus.
a) True
b) False
Answer: a
Explanation: Yes, at the bus three phase system the three-phase fault MVA is always higher than the LG fault.
8. The charging current of a 400 kV is _____ that of 220 kV line of the same length.
a) more than
b) less than
c) equal to
d) none of the mentioned
Answer: a
Explanation: Line charging current is proportional to voltage.
9. Voltage regulation in the power system is __________
a) rise in voltage at receiving end
b) dip in voltage at receiving end
c) rise in voltage at sending end
d) dip in voltage at sending end
Answer: a
Explanation: VR is rise in voltage at receiving end for a transmission line.
10. Voltage regulation becomes negative for a ______load.
a) leading
b) lagging
c) zero power factor
d) unity power factor
Answer: a
Explanation: VR will be negative for a leading load at a receiving end.
This set of Power Systems Questions and Answers for Freshers focuses on “Inductance of Composite Conductor Lines – 2”.
1. Based on the below given phasor diagram, the condition for the zero voltage regulation occurs at ______________
power-systems-questions-answers-freshers-q1
a) OC = OA
b) OC > OA
c) OC = OD
d) DC = AB
Answer: a
Explanation: Zero VR occurs when both the emf and the load voltage are equal.
2. In the below given phasor diagram representation, the angle sine for the condition of zero voltage regulation will be given by ___________
power-systems-questions-answers-inductance-composite-conductor-line-2-q2
power-systems-questions-answers-inductance-composite-conductor-line-2-q2-options
Answer: a
Explanation: Geometrically sin = AD/OA = /|Vr|
The below given phasor diagram is for question number 3, 4 and 5
power-systems-questions-answers-inductance-composite-conductor-line-2-q3-q4-q5
3. In the phasor diagram representation, the angle for the condition of zero voltage regulation will be given by _______________
power-systems-questions-answers-inductance-composite-conductor-line-2-q3-options
Answer: a
Explanation: It is geometrically sin = AD/OA = /|Vr|
4. In the phasor diagram, the angle Ф r such that zero voltage regulation occurs at the receiving end of a transmission line for a leading load, is given as __________
power-systems-questions-answers-inductance-composite-conductor-line-2-q4
Answer: a
Explanation: It is geometrically sin = AD/OA = /|Vr|.
power-systems-questions-answers-inductance-composite-conductor-line-2-q4-exp
5. In the phasor diagram, the angle Ф r such that zero voltage regulation occurs at the receiving end of a transmission line for a lagging load, is given as ___________
power-systems-questions-answers-inductance-composite-conductor-line-2-q5
Answer: b
power-systems-questions-answers-inductance-composite-conductor-line-2-q5-exp
6. For a transmission line under study of failure analysis, it is observed that the current at the receiving end is same as that of the sending end, then what can be concluded about the nature of the transmission line?
a) It is short TL
b) It is medium TL
c) It is long TL
d) Current is always same at the receiving end and the sending end.
Answer: a
Explanation: It is a short transmission line as the capacitance considered is zero and so the line charging current is also zero.
7. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is ______
a) 11.68 kV
b) 7.62 kV
c) 14.4 kV
d) 12.2 kV
Answer: a
Explanation: Current, I = 5000/
=625 A
V s = |V r |+|I|*(RcosФ r + XsinФ r )
= 10000+625
= 11.68kV.
8. When the frequency of the system is increased, the charging MVAR of a system will __________
a) increase
b) decrease
c) remain constant
d) cannot be said
Answer: a
Explanation: Increasing the frequency decreases the reactance and thus charging current increases and so the MVAR.
9.Taking a case study for the long line under no load condition, the receiving end voltage is ____________
a) more than the sending-end voltage
b) less than the sending-end voltage
c) equal to the sending-end voltage
d) it will not be affected by the loading
Answer: a
Explanation: Due to Ferranti effect, the voltage will be more at receiving end in a LTL.
10. While given receiving-end voltage for a long transmission line, the sending-end voltage is more than the actual is found out using _____________
a) Nominal-pi method
b) Nominal-T method
c) Load end capacitance method
d) Any of the mentioned
Answer: a
Explanation: In the nominal pi method, the losses are minimum.
This set of Power Systems Interview Questions and Answers for freshers focuses on “Inductance of Composite Conductor Lines – 3”.
1. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is 11.68 kV. The voltage regulation will be _______
a) 16.8 %
b) 18.8%
c) 21.75%
d) 12.8%
Answer: a
Explanation: VR = *100/10 = 16.8 %.
2. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. Identify the transmission line and the voltage regulation.
a) STL, 11.68%
b) MTL, 11.68
c) STL, 21.5%
d) MTL, 14.2%
Answer: a
Explanation: It is a short transmission line.
Current, I = 5000/=625 A
V s = |V r |+|I|*(RcosФ r + XsinФ r )
= 10000+625
= 11.68kV
VR = *100/10 = 16.8 %.
3. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is 11.68 kV. The half the voltage regulation will be _____________
a) 8.4 %
b) 16.8 %
c) 14.2%
d) 10.5%
Answer: a
Explanation: VR = *100/10 = 16.8 %
Half the VR = 16.8/2 % = 8.4%.
4. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is 11.68 kV. The new sending end voltage at the half the voltage regulation is _____________
a) 10.84 kV
b) 11.84 kV
c) 8.84 kV
d) 16.2 kV
Answer: a
Explanation: VR = *100/10 = 16.8 %
Half the VR = 16.8/2 % = 8.4%
power-systems-interview-questions-answers-freshers-q4
5. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is 11.68 kV. If the voltage regulation is reduced to 50%, then the power factor at this operation mode will be _________________
a) 0.95
b) 0.92
c) 0.74
d) 0.90
Answer: a
Explanation: VR = *100/10
VR = 16.8 %
Half the VR = 16.8/2 %
Half the VR = 8.4%
power-systems-interview-questions-answers-freshers-q4
*1000 = |I|*( RcosФ r + XsinФ r ) …
I = 5000/(cosФ r *10) …
Solving above eqaution
Ф r = 18.04°
Cos Ф r = 0.9508, lagging.
6. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is 11.68 kV. If the voltage regulation is reduced to 50%, then the power factor angle at this operation mode will be _____________
a) 18.04°
b) 8.04°
c) 21.06°
d) 12°
Answer: a
Explanation: VR = *100/10
VR = 16.8 %
Half the VR = 16.8/2 %
Half the VR = 8.4%
power-systems-interview-questions-answers-freshers-q4
*1000 = |I|*(RcosФ r + XsinФ r ) …
I = 5000/(cosФ r *10) …
Solving above equation
Ф r = 18.04°.
7. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is 11.68 kV. If the voltage regulation is reduced to 50%, then the power factor at this operation mode will be ____________
a) 0.95, lagging
b) 0.92, leading
c) 0.95, lagging
d) 0.90, leading
Answer: a
Explanation: VR = *100/10
VR = 16.8 %
Half the VR = 16.8/2 %
Half the VR = 8.4%
power-systems-interview-questions-answers-freshers-q4
*1000 = |I|*(RcosФ r + XsinФ r ) …
I = 5000/(cosФ r *10) …
Solving above equation
Ф r = 18.04°
Cos Ф r = 0.9508, lagging.
8. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is 11.68 kV. If the voltage regulation is reduced to 50%, then the power factor angle at this operation mode will be ________
a) 18.04°, lagging
b) 18.04°, leading
c) 21.06°, leading
d) 21.06°, lagging
Answer: a
Explanation: VR = *100/10
VR = 16.8 %
Half the VR = 16.8/2 %
Half the VR = 8.4%
power-systems-interview-questions-answers-freshers-q4
*1000 = |I|*(RcosФ r + XsinФ r ) …
I = 5000/(cosФ r *10) …
Solving above equation
Ф r = 18.04°, lagging.
9. A single phase 50 hz, generator supplies an inductive load of 5 MW at a power factor of 0.8 lagging using OHTL over 20 km. The resistance and reactance are 0.39Ω and 3.96 Ω. The voltage at receiving station is maintained at 10 KV. The sending end voltage is 11.68 kV. If the voltage regulation is reduced to 50%, then the receiving end current at this operation mode will be _____________
a) 526 A
b) 549 A
c) 521 A
d) 580 A
Answer: a
Explanation: VR = *100/10
VR = 16.8 %
Half the VR = 16.8/2 %
Half the VR = 8.4%
power-systems-interview-questions-answers-freshers-q4
*1000 = |I|*(RcosФ r + XsinФ r ) …
I = 5000/(cosФ r *10) …
Solving above equation
Ф r = 18.04°, lagging
I = 526 A.
10. Suppose the transmission line is loaded with its surge impedance, the receiving-end voltage is greater than sending end voltage.
a) True
b) False
Answer: b
Explanation: It will be equal.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Parallel Circuit Three Phase Lines”.
1. Nominal-T and nominal-π are equivalent to each other.
a) True
b) False
Answer: b
Explanation: Nominal-T and nominal-π are not equivalent to each other. They can’t be interchanged.
2. For the circuit representation of a transmission line below, the transmission line T-matrix will be ___________
power-systems-questions-answers-parallel-circuit-three-phase-line-q2-dia
power-systems-questions-answers-parallel-circuit-three-phase-line-q2-options
Answer: a
Explanation: Applying KVL and KCL,
Vs = Vr
Is = Y * Vs + Ir.
3. For the circuit representation of a transmission line below, the transmission line T-matrix will be power-systems-questions-answers-parallel-circuit-three-phase-line-q3-quest . Then AB – CD value will be _________
power-systems-questions-answers-parallel-circuit-three-phase-line-q3-diagram
a) Y
b) 1
c) -Y
d) 1-Y
Answer: a
Explanation: Applying KVL and KCL,
Vs = Vr
Is = Y * Vs + Ir
AB-CD = 0-Y = -Y.
4. The transfer of the reactive power over a line mainly depends upon _____
a) Vr
b) Vs
c) |V s | – |V r |
d) Power angle
Answer: c
Explanation: Reactive power flow depends on the |Vs|-|Vr|.
5. For a medium transmission line system if the sending end line voltage is 143 kV with the line impedance as 101.24∠74° Ω and shunt admittance of 7.38*10-4∠90° Ω-1.Then the no load line voltage at the receiving end would be _________
a) 148.3 kV
b) 140.8 kV
c) 149.2 kV
d) 132 kV
Answer: a
power-systems-questions-answers-parallel-circuit-three-phase-line-q5-exp
6. For a medium transmission line system if the sending end line voltage is 143 kV with the line impedance as 101.24∠74° Ω and shunt admittance of 7.38*10-4∠90° Ω-1 delivering 25 MVA at 0.8 power factor lagging in nature to the load at 132 kV. The voltage regulation is ___________
a) 12.3
b) 12.8
c) 14.2
d) -2.3
Answer: a
power-systems-questions-answers-parallel-circuit-three-phase-line-q5-exp
Voltage regulation = /132 = 12.3%.
7. For the lines more than 250 km, the parameters of a line are considered not ______ but _____
a) lumped , distributed
b) distributed, lumped
c) lumped, non uniform lumped
d) uniform, lumped
Answer: a
Explanation: For long transmission lines, the parameters are considered uniformly distributed.
8. Which of the parameters of a long transmission line and medium transmission lines are same?
a) A and D
b) B, C
c) Only A
d) Only D
Answer: a
Explanation: A and D parameters of LTL and MTL are almost same.
9. With 100% series compensation of the transmission lines, which of the following effects are observed?
Low transient voltage
High transient current
The current is series resonant at power frequency
a) ,
b) ,
c) , ,
d)
Answer: a
Explanation: 100% compensation of the line results in high transient current at power frequency.
10. With 100% series compensation of the transmission lines, which of the following effects are not observed?
Low transient voltage
High transient current
The current is series resonant at power frequency
a) ,
b)
c) , ,
d)
Answer: b
Explanation: 100% compensation of the line results in high transient current at power frequency.
11. Estimate the transmission line parameters , for the given distributed network.
power-systems-questions-answers-parallel-circuit-three-phase-line-q11
power-systems-questions-answers-parallel-circuit-three-phase-line-q11-options
Answer: a
Explanation: Vs= Z1*Is + Y -1 *
Vr = Z2*Ir + Y-1*
VY = Is+Ir
Solving above equation, we get
power-systems-questions-answers-parallel-circuit-three-phase-line-q11-exp
12. Estimate the transmission line parameters , for the given distributed network and find AB-CD.
power-systems-questions-answers-parallel-circuit-three-phase-line-q12
a) 1
b) Y
c) Y-Z1Z2
d) 0
Answer: 1
Explanation: Vs= Z1*Is + Y -1 *
Vr = Z2*Ir + Y-1*
VY = Is+Ir
Solving above eq, we get
power-systems-questions-answers-parallel-circuit-three-phase-line-q11-exp
AD-BC = 1.
13. Estimate the transmission line parameters , for the given distributed network.
power-systems-questions-answers-parallel-circuit-three-phase-line-q13-diagram
power-systems-questions-answers-parallel-circuit-three-phase-line-13-options
Answer: a
Explanation: Applying KVL in the middle loop and KCL at the two nodes, we will get
power-systems-questions-answers-parallel-circuit-three-phase-line-q13-exp
14. Surge impedance for 400ohms implies for a transmission line that ___________
a) line can be theoretically loaded up to 400ohms
b) line can be practically loaded up to 400ohms
c) open circuit impedance of 400ohms
d) short circuit impedance of 400ohms
Answer: a
Explanation: Surge impedance decides the maximum value for a transmission line loading.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Bundled Conductors”.
1. The larger power can be transmitted over a line with fixed voltage profile when ______
a) compensators are installed
b) negative VAR is fed
c) positive VAR is fed
d) compensators are installed and postive VAR is fed
Answer: d
Explanation: Compensators allow the flow of a large power through the TL by feeding positive VAR into the system.
2. A rectangular voltage wave is impressed on a long overhead line, with the far end of the line being open circuited. After reaching line end, the current is _________
a) current is reflected back with positive but voltage with negative sign
b) current is reflected back with negative but voltage with positive sign
c) both current and voltage are reflected with negative sign
d) both current and voltage are reflected with positive sign
Answer: b
Explanation: For open circuited end, ρ = 1; ρ = -1.
3. If OH transmission line of impedance Z1, is terminated with a cable of impedance Z2. The transmission coefficient of the voltage for the travelling wave at the junction of line and cable is ______________
power-systems-questions-answers-bundled-conductor-q3
Answer: a
power-systems-questions-answers-bundled-conductor-a3-exp
4. A 240 kV 2μs rectangular pulse surge on a transmission line has surge impedance of 350 ohms. It approaches a generating station with capacitance of 3000 pF. The transmitted voltage will be ____________
a) 340.5 kV
b) 280 kV
c) 400 kV
d) 480 kV
Answer: a
Explanation: Vt = 2Vi(1-e ) = 2*240*1000(1-e -2*10 -6 /3*350*10 -9 ).
5. In a transmission line system, the feeders act as input to _________
a) distributors
b) service mains
c) transformer sub stations
d) all of the mentioned
Answer: a
Explanation: The feeders have bulk power and they have no tappings. They feed to the distributors.
6. One needs to design the distributors, the parameter which will be considered for the design of it?
a) voltage drop in it
b) current flowing
c) operating voltage
d) operating frequency
Answer: a
Explanation: Distributors work based on the voltage drops measured across them.
7. One would design the feeders of the transmission system based on its ____________
a) current capacity
b) voltage drop
c) operating voltage
d) all of the mentioned
Answer: a
Explanation: Feeders do not have tappings and they are designed on the basis of current flowing through them.
8. The underground transmission and distribution of power is better than the corresponding overhead transmission and distribution in respect of _________
a) appearance and safety
b) maintenance cost
c) frequency of faults
d) appearance, safety, maintenance, frequency
Answer: d
Explanation: All the points are advantageous with respect to overhead transmission line in an underground power transmission system.
9. Before installing any transmission system, one has to decide about the type of the transmission system to be employed. Considering a monetary shortage and economical setup, one would take up _____________
a) underground system
b) overhead system
c) underground or overhead system
d) can be chosen randomly.
Answer: b
Explanation: Underground installation takes a lot of initial cost.
10. The volume of copper required in a transmission system is proportional to _________
a) voltage and power factor
b) power factor
c) voltage
d) current
Answer: a
Explanation: Weight of the copper is proportional to voltage and power factor.
11. While deciding an efficient and economical transmission and distribution system, the preferred distribution system will be _____________
a) single phase, 2 wire
b) two phase, 3 wire
c) three phase, 3 wire
d) three phase, 4 wire
Answer: d
Explanation: For a reliable system, the distribution system should be 4 wire, in case a fault occurs.
12. In India, the preferred poles used in the transmission and distribution is ______
a) Steel poles
b) RCC poles
c) Steel and RCC poles
d) Wood poles
Answer: c
Explanation: The most commonly used poles are steel and RCC poles.
13. Copper has got higher resistivity than aluminium which makes it less used in transmission system.
a) True
b) False
Answer: b
Explanation: Aluminium has higher resistivity over copper.
14. _______ material is used for the making of the ground wire in the transmission system.
a) Galvanised steel
b) Steel
c) Cast iron
d) Aluminium
Answer: a
Explanation: Galvanised steel is used in the ground wire.
15. In emergency cases, another wire is installed in the system, that is widely known as ________________
a) Guy wire
b) Earth wire
c) Line wire
d) Neutral wire
Answer: a
Explanation: Guy wire as the earth route in the emergency earth route.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Skin Effect and Proximity Effect – 1”.
1. Ripple of the DC-output at power converter is ____________
a) maximum value of instantaneous difference between average and instantaneous value
b) minimum value of instantaneous difference between average and instantaneous value
c) average value of output
d) maximum value of instantaneous value
Answer: a
Explanation: Ripple at a power converter is maximum value of instantaneous difference between average and instantaneous value.
2. Smooth reactor is connected between _____________
a) DC output of converter and load
b) load and ground
c) source and input of converter
d) any of the mentioned
Answer: a
Explanation: Smoothening reactor is connected between the dc output and load to provide sinusoidal source current.
3. Which of the above is not a DC link?
a) Monopolar link
b) Bipolar link
c) Homopolar link
d) None of the mentioned
Answer: d
Explanation: All are types of DC link.
4. Monopolar DC link has one energised conductor of positive polarity.
It was ground as return path
Opt the most appropriate.
a) is False & is True
b) is True & is True
c) Both are false
d) is True & is False
Answer: a
Explanation: Negative polarity is preferred on OH lines due to less radio interference.
5. Bipolar link has two conductors
Both conductors have same magnitude of voltage.
a) is False & is True
b) is True & is True
c) Both are false
d) is True & is False
Answer: b
Explanation: Both the statements are correct.
6. If the currents in the two conductors of bipolar HDVC link is same, then _______
a) ground current is zero
b) two poles work independently
c) ground current zero and two poles work independently
d) none of the mentioned
Answer: b
Explanation: When the two conductors in bipolar link are same then ground current is zero and they have no interaction.
7. Homopolar link is employed instead of bipolar link to ___________
a) reduce corona loss
b) reduce radio interference
c) improve reliability
d) all of the mentioned
Answer: a
Explanation: Homopolar link reduces corona loss.
8. Which of the DC links can be operated when a fault occurs in the transmission line?
a) Bipolar link and Homopolar link
b) Monopolar link and Bipolar link
c) Monopolar link
d) Bipolar link
Answer: a
Explanation: 50% of rated power can be supplied.
9. The overvoltage that occur mainly under converter stations are due to _________
Lightening and switching overvoltage
Transients produced in conductors
Overvoltage due to fault clearing
Choose the correct option.
a) , ,
b) ,
c)
d) ,
Answer: a
Explanation: All the statements are correct.
10. Insulator capacitance is does not play significant role in HVDC lines
a) True
b) False
Answer: a
Explanation: There is no capacitive current which flows in HVDC link.
This set of Power Systems Questions and Answers for Experienced people focuses on “Skin Effect and Proximity Effect – 2”.
1. Which of below factor contribute to the more receptibility to pollution of insulators?
a) Ionic current
b) Uniform voltage
c) Electrostatic voltage
d) Ionic current and Electrostatic voltage
Answer: a
Explanation: The ionic current and the electrostatic voltage that develops contributes towards the receptibility of pollution in insulators.
2. More number of insulators are needed in AC line as compared to DC line
a) True
b) False
Answer: b
Explanation: No, DC line need more because of thermal runaway, high unit flashover and contamination.
3. The factors which contribute more to the addition of insulator in HDVC line are ____________
a) high unit flashover
b) contamination
c) thermal runaway
d) high unit flashover, contamination and thermal runaway
Answer: d
Explanation: All the factors add to the insulator addition.
4. What makes porcelein type insulator to be off market?
a) Weight
b) Greater failure rate
c) Self clearing
d) Weight and greater failure rate
Answer: d
Explanation: They have higher probability of fault occurrence and possess larger weight.
5. Most industrially accepted insulators used in HVDC is/are ___________
a) high resistance toughened glass type
b) porcelein type
c) silicon rubber composite type
d) all of the mentioned
Answer: a
Explanation: HRTG is mostly accepted.
6. What is the major problem in current interruption in DC circuit?
a) No natural zero current
b) Extra energy stored in circuit
c) High flashover
d) All of the mentioned
Answer: a
Explanation: There is no natural zero current in DC circuit which poses problem.
7. A two conductor DC line is more reliable than a three conductor AC line.
a) True
b) False
Answer: a
Explanation: A two conductor DC can always find path through earth or sea than AC system.
8. Stunt capacitors are installed on ____ and smoothing reactor is installed in ____ in TL.
a) AC side, DC side
b) DC side, DC side
c) AC side, AC side
d) DC side, AC side
Answer: a
Explanation: Shunt capacitors are connected at dc side while inductor at ac.
9. There is no requirement of reactive power at the converter station of a HVDC link.
a) True
b) False
Answer: a
Explanation: There is requirement of reactive power due to phase shift between fundamental as current and voltage and commutation process.
10. _______ polarity is preferred on OH lines due to less radio interference.
a) Negative
b) Positive
c) Ground
d) Any of the mentioned
Answer: a
Explanation: Negative polarity is preferred on overhead lines.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Electric Field and Potential of a Long Straight Conductor – 1”.
1. Shunt admittance of a transmission line comprises of ______
a) capacitance with conductance
b) capacitance with inductance
c) resistance with inductance
d) capacitance with susceptance
Answer: a
Explanation: Shunt admittance is capacitance with conductance in the branch.
2. Conductance is the result of the leakage over the surface of insulators.
a) True
b) False
Answer: a
Explanation: Conductance comes into the picture due to the leakage current over the conductor’s surface.
3. Charging current in the transmission line is _______________
a) drawn at open as well as closed end of the transmission line
b) drawn at closed end of the transmission line
c) drawn at open end of the transmission line
d) drawn at the shunt capacitance at closed end of transmission line.
Answer: a
Explanation: Charging current in transmission line is drawn even when the far end of the TL is open.
4. A three phase 50 Hz transmission line has flat horizontal spacing with 3.5 m between adjacent conductors. The conductors are No. 2/0 hard drawn copper . The voltage f the line is 110 kV. The capacitance to neutral per kilometre of line is
a) 0.00826 μF/km
b) 0.0826 μF/km
c) 0.01652 μF/km
d) 0.1652 μF/km
Answer: a
Explanation:
power-systems-questions-answers-electric-field--potential-long-straight-conductor-1-q4
5. A three phase 50 Hz transmission line has flat horizontal spacing with 3.5 m between adjacent conductors. The conductors are No. 2/0 hard drawn copper . The voltage f the line is 110 kV. The capacitive reactance to neutral per kilometre of line is ____________
a) 0.384 x 106 Ω/km to neutral
b) 0.768 x 106 Ω/km to neutral
c) 0.284 x 106 Ω/km to neutral
d) 0.642 x 106 Ω/km to neutral
Answer: a
Explanation:
power-systems-questions-answers-electric-field--potential-long-straight-conductor-1-q5
6. A three phase 50 Hz transmission line has flat horizontal spacing with 3.5 m between adjacent conductors. The conductors are No. 2/0 hard drawn copper . The voltage f the line is 110 kV. The line charging current per km of the line is _______________
a) 0.17 A/km
b) 0.34 A/km
c) 0.24 A/km
d) 0.48 A/km
Answer: a
Explanation:
power-systems-questions-answers-electric-field--potential-long-straight-conductor-1-q6
7. A three phase 50 Hz transmission line has flat horizontal spacing with 3.5 m between adjacent conductors. The conductors are No. 2/0 hard drawn copper . The voltage f the line is 110 kV. The line charging current per conductor of the line is _____________
a) 0.085 A/km
b) 0.17 A/km
c) 0.12 A/km
d) 0.24 A/km
Answer: a
Explanation:
power-systems-questions-answers-electric-field--potential-long-straight-conductor-1-q7
C n = 0.00826 μF/km
X n = 1/ωC n
X n = 1/(100π* .284 *10 -6 )
X n = 0.384 x 106 Ω/km to neutral
Charging current = Vn/Xn
Charging current = *1000/(0.384 *10 6 )
Charging current = 0.17 A/km
Charging current per conductor = I/2
Charging current per conductor = 0.17/2
Charging current per conductor = 0.085 A/km.
8. A three phase 50 Hz transmission line has flat horizontal spacing with 3.5 m between adjacent conductors. The conductors are No. 2/0 hard drawn copper . The voltage f the line is 110 kV. The reactive volt amperes generated by the line is
a) 31.4 kVAR
b) 62.8 kVAR
c) 42 kVAR
d) 56 kVAR
Answer: a
Explanation:
power-systems-questions-answers-electric-field--potential-long-straight-conductor-1-q7
C n = 0.00826 μF/km
X n = 1/ωC n
X n = 1/(100π* .284 *10 -6 )
X n = 0.384 x 106 Ω/km to neutral
Reactive volt amperes generated by the line = 2 /X c
Reactive volt amperes generated by the line = 31.4 kVAR.
This set of Power Systems Interview Questions and Answers for Experienced people focuses on “Electric Field and Potential of a Long Straight Conductor – 2”.
1. If we account for the effect of the presence of the capacitance of the transmission line, then the capacitance ___________
a) increases
b) decreases
c) remains same
d) increases hyperbolically
Answer: a
Explanation: Earth effects increases the capacitance of the system.
2. While estimating the line parameters, the term self GMD is used for the calculation of ______________
a) inductance
b) capacitance
c) conductance
d) inductance, capacitance and conductance
Answer: a
Explanation: Self GMD is used in the calculation of the inductance.
3. The ground effect causes line capacitance to _____________
a) Increase by 0.2%
b) Increase by 2%
c) Decrease by 0.2%
d) Decrease by 2%
Answer: a
Explanation: The effect of the ground is not very significant on the capacitance.
4. If the spacing between the phase conductors is increased, the line capacitance will _______________
a) decrease
b) increase
c) remain same
d) depends on the conductor
Answer: a
Explanation: power-systems-interview-questions-answers-experienced-q4
5. If the length of the transmission line is increased, the line charging current in the TL will _____________
a) increase
b) decrease
c) remain same
d) not be affected
Answer: a
Explanation: If the length of the TL increases, then the line admittance will decrease, so the line charging current will decrease.
6. On applying the alternating sine wave as the input to the line, the line capacitance draws _____________
a) leading sinusoidal current
b) lagging sinusoidal current
c) current in phase with voltage
d) depends on the receiving end load
Answer: a
Explanation: The line current will be leading sinusoidal current.
7. The capacitance becomes significant for the __________
a) long transmission line
b) medium transmission line
c) short transmission line
d) cannot be determined
Answer: a
Explanation: Capacitance parameter is highly important for long transmission line due to the charging current flowing in the LTL.
8. The method of the images is applied to find the __________________
a) calculation of capacitance
b) calculation of inductance
c) calculation of resistance
d) calculation of effect of the earth on capacitance
Answer: d
Explanation: Method of images given by Lord Kelvin is used to calculate the effect of the earth on capacitance.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Capacitance of a Two-Wire Line”
1. The presence of ozone while the corona has occurred, can be found using ________
a) pressure
b) hissing noises
c) faint luminous glow of bluish colour
d) all of the mentioned
Answer: d
Explanation: The ozone can be easily detected by all the mentioned effects occurring in the system.
2. The corona has only disadvantages to the transmission system.
a) True
b) False
Answer: b
Explanation: Corona is helpful while the surges are there.
3. The very peculiar advantage of corona in the circuit can be ___________
a) reduction in steepness of surge fronts
b) improvement of power factor
c) reduction in radio interference
d) reduction in steepness, radio interference and improvement of PF
Answer: a
Explanation: Corona reduces the surge occurring in the system.
4. When the ozone gas is produced as a by product of corona, that causes _______
a) corrosion of wires
b) reduction of power factor
c) increase of power factor
d) improvement of regulation
Answer: a
Explanation: Ozone gas corrodes the metals.
5. Critical voltage limit of the transmission line can be increased by ____________
a) increasing conductor’s radius
b) increasing conductor spacing
c) reducing conductor spacing
d) reducing radius of conductor
Answer: a
Explanation: Vα 1/r.
6. In a transmission system, the transmission parameters of distribution is/are ___________
a) resistance
b) inductance
c) capacitance and shunt conductance
d) resistance, inductance, capacitance and shunt conductance
Answer: d
Explanation: R, L, C, G are the distribution constants.
7. Following effects of the transmission lines
Skin effect
Corona
Proximity
The effective resistance of the conductor is increased by __________
a) ,
b) ,
c) ,
d) , ,
Answer: d
Explanation: Effective resistance increases by skin effect, corona as well as proximity effect.
8. _______ is neglected while carrying out short transmission line analysis.
a) Shunt admittance
b) Power losses
c) Series impedance
d) None of the mentioned
Answer: a
Explanation: Shunt admittance is neglected.
9. We transpose high voltages especially while transmitting so that the __________
a) phase voltage imbalances can be minimised
b) corona losses are reduced
c) voltage drop is minimised
d) all of the mentioned
Answer: a
Explanation: Transposition reduces the phase voltage imbalances by cancelling their effects.
10. While modelling a short transmission line of the overhead lines, line resistance and inductances are only considered because the line capacitance is ___________
a) zero
b) finite but small
c) finite but large
d) infinite
Answer: b
Explanation: Capacitance for such a distance is small and negligible.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Capacitance of a Three-phase Line”.
1. For a transmission line of length not more than 80 km, then it is convenient to lump the capacitance at ________
a) receiving end
b) sending end
c) midpoint
d) anywhere long the line
Answer: a
Explanation: The capacitance should be best lumped at the receiving end for the simpler calculations.
2. At the no load conditions, the current is detected in the transmission line. This can be attributed due to __________
a) capacitance effect
b) proximity effect
c) corona effect
d) back flow through earth
Answer: a
Explanation: At the no load current the shunt connected capacitance allows the flow of the current through the circuit.
3. Identify the characteristics of the Ferranti effect.
Flow of unduly heavy current
It occurs at unloaded condition
Rise in the receiving end voltage
a) ad
b) ad
c) ad
d) ad
Answer: d
Explanation: Ferranti effect occurs at no load condition and it causes rise in voltage.
4. Ferranti effect is very prominent in occurrence in what type of transmission line?
a) Long and unloaded
b) Short and loaded
c) Long and unloaded
d) Short and unloaded
Answer: a
Explanation: Ferranti effect occurs more in long TL and especially when they are not loaded.
5. The transmission line parameters ABCD for a three phase transposed line with passive and linear elements are ____________
a) always equal
b) never same
c) A and D are same
d) B and C are same
Answer: a
Explanation: The A and D parameter will only be constant.
6. For a general transmission system, the calculated parameter A for a medium transmission line has magnitude _____________
a) close to but less than 1
b) close to but more than 1
c) average of B and C parameter
d) none of the mentioned
Answer: a
Explanation: |A| < 1 but less than 1.
7. The impedance known as surge impedance and characteristic impedance are same.
a) True
b) False
Answer: a
Explanation: Both the impedances are same.
8. Characteristic impedance of a transmission line depends upon ____________
a) geometrical configurations of conductor
b) shape of conductor
c) conductivity
d) surrounding of the conductor.
Answer: a
Explanation: Characteristic impedance of a transmission line will depend on conductor configuration.
9. What will happen when the characteristic impedance of a transmission line is equal t the load impedance ______________
a) all the given energy will be absorbed by the load
b) all the given energy will be transferred to load
c) system will undergo resonance
d) all the given energy will be lost in transmission losses.
Answer: a
Explanation: When the characteristic impedance will be same as load then the load will absorb all the energy.
10. The transmission capacity of a line at 50 Hz frequency as compared to that at 60 Hz is ______
a) higher
b) lower
c) same
d) can’t be decided
Answer: a
Explanation: Due to drop in frequency the losses will reduce.
11. Use of additional shunt capacitor can be made for increasing the capability of the line as it will ______
a) reduce surge impedance
b) increase phase shift
c) increase the angle α
d) all of the mentioned
Answer: a
Explanation: Due to addition of capacitance, the impedance will reduce and power capability will increase.
12. To increase the transmission capability of a high voltage long line ____________
a) series reactance can be reduced
b) resistance can be increased
c) resistance can be decreased
d) shunt admittance can be reduced
Answer: a
Explanation: Transmission capability is inversely proportional to the reactance.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Effect of Earth on the Three Phase Transmission Line Capacitance – 1”.
1. Transmission efficiency of a transmission line increases with the _____________
a) decrease in power factor and voltage
b) increase in power factor and voltage
c) increase in power factor but the decrease in voltage
d) increase in voltage only power factor remains constant
Answer: b
Explanation: Increasing the power factor and voltage reduces the losses and hence improves the efficiency.
2. Surge impedance of a transmission line is the impedance at the time of breakdown of voltage.
a) True
b) False
Answer: b
Explanation: Surge impedance is the characteristic impedance of a TL.
3. When the transmission line is lousy, then its characteristic impedance will not depend on which of the following?
a) Length
b) Operating frequency
c) Sub synchronous frequency
d) Length and Sub synchronous frequency
Answer: d
Explanation: For a lousy line, the characteristic impedance will be independent of its sub synchronous frequency and length.
4. If the transmission line is lossless, then its characteristic will be _________
a) √
b) √LC
c) √
d) √
Answer: a
Explanation: The characteristic impedance for the lossless lines is given by √ because the resistance is zero.
5. The surge impedance of multiple conductor lines as compared to single line is _______
a) higher
b) lower
c) same
d) length dependent
Answer: b
Explanation: Due to the reduced GMD, the impedance decreases and so the surge impedance.
6. When ______ then the transmission line will act as a distortion less line.
a) RC = GL
b) RG = LC
c) R = G
d) Cannot be determined
Answer: a
Explanation: When both the time constants become same, then the transmission will behave like distortion less line.
7. It is intended to increase the power despatch of the existing transmission line. Then what can be the most appropriate solution for improving it?
a) Installing series capacitors
b) Installing shunt capacitor
c) Installing shunt reactor
d) Installing series reactor
Answer: a
Explanation: Series capacitors reduce the power as power-systems-questions-answers-earth-effect-transmission-line-capacitance-1-q7
8. Which of the following situations is very useless when the series capacitors to the transmission line are of little use?
a) When the VAR requirement is small
b) When the VAR requirement is large
c) When the VAR requirement is varying
d) Cannot be determined
Answer: a
Explanation: Because capacitance is usually neglected for a small transmission line.
9. Reactive power requirement of a power transmission system depends on __
a) Power angle δ
b) |V s |-|V r |
c) V s
d) V r
Answer: b
power-systems-questions-answers-earth-effect-transmission-line-capacitance-1-q9
10. When do we use conduit pipe in the transmission of power?
a) Unsheathed cables
b) Armoured cables
c) PVC sheathed cables
d) All of the mentioned
Answer: a
Explanation: It is used in protection of wires and cables for underground transmission.
This set of Power Systems test focuses on “Effect of Earth on the Three Phase Transmission Line Capacitance – 2”.
1. The bedding on a cable will consist of _____
a) jute strands
b) hessian tapes
c) paper tape compounded
d) all of the mentioned
Answer: d
Explanation: All the mentioned are used in protecting a cable and used around the conductor.
2. A designer wanted to design the insulator for the underground cable, then the estimation of thickness of the insulator will depend on ______________
a) Operating voltage
b) Current to be carried
c) Power factor
d) Operating Voltage and current to be carried
Answer: a
Explanation: Insulation is always function of the voltage applied to it.
3. While choosing the insulating materials for the UG cables, it must not possess which of the following characteristics?
a) High water absorption, high dielectric strength
b) Low thermal coefficient
c) Low permittivity
d) Cannot be determined
Answer: a
Explanation: An insulator should not have high water retention capability.
4. While choosing the insulating materials for the UG cables, it should possess which of the following characteristics?
a) High water absorption, high dielectric strength
b) Low thermal coefficient
c) Low permittivity, high voltage rupturing ability
d) Low thermal coefficient, Low permittivity, high voltage rupturing ability
Answer: d
Explanation: An insulator should not have high water retention capability.
5. Consider the two statements and choose the options.
Transmission of electrical power by dc is economical than with the ac
In case of dc transmission, there is no charging current which contributes to continuous load.
a) and are true
b) is only true
c) is only true
d) and are false
Answer: a
Explanation: Both the statements are correct. DC transmission is economical while its installation is difficult and expensive.
6. We can improve the string efficiency by using long cross arms.
a) True
b) False
Answer: a
Explanation: It reduces the ratio of capacity to earth to capacity per insulator.
7. Corona reduces the transient surges due to _________
a) it dissipates the stored charges
b) it absorbs the charges
c) it raises the electric gradient
d) all of the mentioned
Answer: a
Explanation: Due to the charge dissipation, corona is advantageous in reducing the voltages.
8. SL type cables, over H-type cables have advantage of mostly ____________
a) possibility of bending of cables
b) less tendency of oil drainage
c) easy transportation
d) reduced possibility of core faults
Answer: b
Explanation: Lesser tendency of drainage of the SL-type and H-type cables make them more in demand.
9. Control of the reactive power flow in the circuit is essential for maintaining the good voltage regulation.
a) True
b) False
Answer: a
Explanation: Reactive power controls the voltage profile of the transmission line.
10. Screened type cables have _____ possibilities of core to core faults when compared to belted type cables.
a) lesser
b) more
c) same
d) cannot be decided
Answer: a
Explanation: Because metal sheathed core has greater core to core thickness for a given diameter.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Geometric Mean Distance and Geometric Mean Radius – 1”.
1. Which of the system would require more insulation, a 400 kV ac line or 400 kV dc line?
a) 400 kV ac
b) 400 kV dc
c) Both will need same level of insulation
d) Data is insufficient to decide
Answer: a
Explanation: In ac system, the peak value attained will be 400*√2= 564 kV.
2. The amount of dc compensation needed by a 400 kV dc line for transmitting the data over 300 km having resistance as 5 ohms?
a) 400 var
b) 564 var
c) 600 VAR
d) None of the mentioned
Answer: a
Explanation: A dc line does not require any reactive compensation.
3. Steady state problem is not very serious problem in dc transmission line system due to which of the following systems?
a) No reactive compensation
b) Only resistance drop
c) Stable voltage regulation
d) No reactive compensation, resistance drop, voltage regulation
Answer: a
Explanation: Due to all the above reasons, mainly the reactive power compensation there is very less variation in stability.
4. DC line transmission can be used to provide _______ link.
a) asynchronous
b) synchronous
c) lossless
d) none of the mentioned
Answer: a
Explanation: As dc link provides to connect to different frequencies of the operating buses. It can transfer power frequency independent.
5. Low short circuit current is required in dc system
Fast control of the converter switches cannot effectively control the damping of the oscillations.
Choose the most appropriate.
a) and both are true
b) Only is false
c) Only is false
d) Both statements are false
Answer: b
Explanation: It’s an advantage the using converters in dc link can control the fast damping of the oscillations which occur in ac systems.
6. The reactive power demand of the converters in HVDC can be provided by ___________
a) AC filters
b) Shunt Capacitors
c) SVC
d) AC Filters, Shunt Capacitors and SVC
Answer: d
Explanation: Reactive power demand by the HVDC system can be fulfilled by all the mentioned equipment’s.
7. As compared to the HVDC line, the corona and radio interference in a HVAC line are ____
a) more
b) lesser
c) same
d) cannot be determined
Answer: a
Explanation: The corona and radio interference losses are more in ac system.
8. What of the below mentioned statements are incorrect as compared to the HVDC system?
a) Back to back connection is possible
b) More corona losses
c) Distance limitation
d) Extra reactive power compensation
Answer: b
Explanation: Out of all the corona losses are less in HVDC system.
9. It is required to implement the HVDC system using the thyristors in large numbers. Why it becomes necessary to use a large number of thyristor switches?
a) Due to low voltage rating of thyristor switches
b) Due to low current rating of thyristor switches
c) Due to lack of response for open circuit fault
d) Cannot be determined
Answer: a
Explanation: Thyristors have low voltage rating and to achieve high voltage, a series of switches that have to used.
10. The corona loss on a particular system at 50 Hz is 1 kW/phase per km. The corona loss on the same system in case of DC transmission will be ____________
a) Zero
b) 0.5 kW/phase/km
c) 0.33 kW/phase/km
d) 0.6 kW/phase/km
Answer: c
power-systems-questions-answers-geometric-mean-distance-1-q10
This set of Power Systems Quiz focuses on “Geometric Mean Distance and Geometric Mean Radius – 2”.
1. The power transmission capability of bipolar lines is approximately ____________
a) same as that of 3-ph single circuit line
b) same as that of 3-ph double circuit line
c) twice to that of 3-ph single circuit line
d) half to that of 3-ph single circuit line
Answer: a
Explanation: Power transmission by bipolar dc line is same as that three phase single line transmission.
2. HVDC system has charging current but no skin effect while transferring the power through it.
a) True
b) False
Answer: b
Explanation: Skin effect as well as the charging effect, both are absent in dc transmission system.
3. As depicted in the figure, the power will be transferred in the system from A to B by a HVDC link as shown in the figure. The voltages are indicated in the figure and I >0, then _______
power-systems-questions-answers-quiz-q3
a) Vab<0, Vcd<0, Vab>Vcd
b) Vab<0, Vcd>0, Vab<Vcd
c) Vab>0, Vcd<0, Vab>Vcd
d) Vab>0, Vcd>0, Vab>Vcd
Answer: d
Explanation: The given situation is such as the current is more than zero, so a positive current will flow from higher voltage to lower voltage.
4. As depicted in the figure, the power is transferred in the system from B to A by a HVDC link as shown in the figure. The voltages are indicated in the figure and I <0, then ______
power-systems-questions-answers-geometric-mean-distance-2-q4
a) Vab<0, Vcd<0, Vab>Vcd
b) Vab<0, Vcd>0, Vab<Vcd
c) Vab>0, Vcd>0, Vab<Vcd
d) Vab>0, Vcd>0, Vab>Vcd
Answer: c
Explanation: The given situation is such as the current is less than zero, so a positive current will flow from higher voltage to lower voltage i.e. from cd to ab.
5. A dc line carries as compared to ac line _____________
a) more power
b) less power
c) same power
d) can’t be decided
Answer: a
Explanation: A dc line carries more power as compared to ac line.
6. Back to back HVDC is used to ___________
a) increase the transmission capability
b) decrease line losses
c) provide a stable connection
d) reduce the voltage drop
Answer: c
Explanation: Back to Back connection in HVDC will provide a stable connection.
7. HVDC transmission would require which of the following equipment’s?
Pulse converter
AC filter
DC filter
DC generator
a)
b) ,
c) ,
d) ,
Answer: a
Explanation: Only pulse converter is needed by HVDC transmission system.
8. As compared with the HVAC lines, dc transmission system is free from ___________
a) inductance
b) capacitance
c) phase displacement
d) all of the mentioned
Answer: d
Explanation: All the factors which involve frequency will be absent in dc system as in f= 0 in dc.
9. Mostly the high voltage transmission is provided by overhead lines due to _____________
a) low cost
b) low losses
c) easy installation
d) all of the mentioned
Answer: a
Explanation: Due to economic criteria, the high voltage transmission is done by overhead lines.
10. Consider the below statements and choose the most appropriate.
Guy wire is galvanised.
Guy wire should possess high conductivity.
At installation it makes an angle of 40-60 degrees with earth.
a) , and are true
b) Only and are true
c) and are true
d) and are true
Answer: a
Explanation: All the statements about the guy wire are true.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Effect of Synchronous Machine Excitation – 1”.
1. The synchronous machine is operating at a normal condition at the generating system, then the angle between rotor axis and the stator magnetic axis is _____________
a) Load angle
b) Power factor angle
c) Impedance angle
d) None of the mentioned
Answer: a
Explanation:
power-systems-questions-answers-synchronous-machine-excitation-1-q1
2. The angle shown in the figure depends on which of the following given options?
power-systems-questions-answers-synchronous-machine-excitation-1-q2
a) Loading of the system
b) Power factor
c) Operating frequency
d) Power factor, operating frequency, loading of the system
Answer: a
Explanation: Load angle depends on the loading of the system, as the load in added or decreased, the synchronous machine will accelerate or decelerate with respect to stator field.
3. Swing equation is very famous for describing the relation between the ___________
a) rotor motion and stator field
b) stator and rotor field
c) load angle and rotor field
d) moment of inertia and rotor motion
Answer: a
Explanation: Swing equation describes the relative motion between rotor load angle with respect to stator field as a function of time.
4. Swing equation which describes the relative motion of the rotor of the machine, is a __________
a) linear and second-order differential equation
b) non linear and second-order differential equation
c) non linear and first-order differential equation
d) non linear and hyperbolic equation
Answer: b
power-systems-questions-answers-synchronous-machine-excitation-1-q4
Hence it is a non linear second order differential equation.
5. A variation in the power transfer had been observed at the generating station while power exchange process due to ______ and is known as ______
a) swing of the machine, inertial response
b) sub synchronism, hunting
c) sub synchronism, inertial response
d) swing of the machine, falling out of the rotor
Answer: a
Explanation: The power exchange between the mechanical rotor and the electrical grid due to the swing of the rotor is called inertial response.
6. Why the angle δ, rotor angle is famously called as the load angle in the equation of rotor dynamics?
a) Due to power exchange is a function of δ
b) Because it dictates the reactive power compensation
c) Due to load variations
d) No dependency on the load dynamics
Answer: a
Explanation: Rotor angle is the emf angle and power is a function of it.
7. The transient stability and the steady state stability of a power transmission system ________
a) maintain synchronism between machine and tie lines at all the circumstances
b) maintains frequency exactly at 50 Hz
c) maintain voltage regulation precisely
d) all of the mentioned
Answer: a
Explanation: Transient stability and steady state stability maintain synchronism between the generating station and tie line.
8. We can say a system is stable at steady state is not affected by ____________
a) line losses
b) line reactance
c) generator reactance
d) excitation of alternators
Answer: a
Explanation: Line losses do not affect the stability limit of the system.
9. The transient instabilities can occur in a system by ___________
a) Sudden load changes
b) Switching operation
c) Faults
d) Suddenn load changes, switching operation and faults
Answer: d
Explanation: All the mentioned factors affect the transient stability of a system.
10. Post a three phase fault that occurs in a system, then its transient stability can be examined using ___________
a) solution of swing equation
b) equal area criterion
c) solution of swing equation and equal area criterion
d) solution of swing equation or equal area criterion
Answer: a
Explanation: Swing equation provides the rotor dynamics at the transient conditions.
This set of Power Systems MCQs focuses on “Effect of Synchronous Machine Excitation – 2”.
1. How can we check upon the transient stability of a power system?
a) By checking variation in load angle
b) By checking variation of real power with load angle
c) Checking variation in load angle and real power
d) Checking variation in load angle or real power
Answer: c
Explanation: Checking the variation in load angle and real power flow helps in deciding the transient stability.
2.To maintain the transient stability for a power system _____________
power-systems-questions-answers-mcqs-q2
Answer: c
Explanation: The rate of change of load angle must be positive and so the change in real power variation in order to supply the demand.
3. How can we improve the steady state stability of the synchronous generator for a better performance?
a) Increasing the excitation
b) Increasing reactance
c) Decreasing moment of inertia
d) Increasing moment of inertia
Answer: a
Explanation: P = EV/X.
4. There is 2-machine model having losses too, with their transfer impedance being resistive. The maximum value of sending power P 1max and maximum receiving end power P 2max will take place with power angle ‘δ’ such that
a) Both P 1max and P 2max will occur at δ<90
b) Both P 1max and P 2max will occur at δ>90
c) P 1max occurs at δ > 90 and P 2max will occur at δ<90
d) P 1max occurs at δ < 90 and P 2max will occur at δ>90
Answer: a
Explanation: Even after connecting parallel machines, their maximum power will occur at load angle lesser than 90 degrees.
5. As per the system given, machine B will receive the active and reactive power from machine A when ______________
a) δ is positive and Va is more than Vb
b) δ is positive and Va is less than Vb
c) δ is positive and Va is same as Vb
d) δ is negative and Va is more than Vb
Answer: a
Explanation: Real power flows from higher to lower δ while the reactive power flows from higher voltage to lower.
6. If there are two machines having moment of inertia M1 and M2, where M1<M2; The possible number of equivalent moment of inertia will be _______________
a) 1
b) 2
c) 3
d) 4
Answer: c
Explanation: M1+M2, M1||M2 and M1-M2.
7. If there are two machines having moment of inertia M1 and M2, where M1<M2; Then one is proposing to add more inertia to the system. Then it will be added to _____________
power-systems-questions-answers-synchronous-machine-excitation-2-q7
a) Machine 1
b) Machine 2
c) Machine 1 and Machine 2
d) Either of Machine 1 and Machine 2
Answer: a
Explanation: Since the inertia is less for machine 1.
8. The measure to improve the transient stability of the power system during the unbalanced or unsymmetrical fault can be taken as ________
a) Single pole switching of CB
b) Excitation control
c) Phase shifting transformer
d) Increasing turbine valve opening
Answer: a
Explanation: Single pole switching of CB allows the immediate isolation of the fault frim the system and thus safeguarding the healthy part.
9. Use of high speed circuit breaker will actually increase the system stability.
a) True
b) False
Answer: a
Explanation: High speed CB immediately cuts off the fault and saves the system to undergo transient oscillations.
10. What does the steady state stability of a power system signify?
a) Maintaining the rated voltage
b) Maintaining rated frequency
c) Maintaining a synchronism between machines and tie-lines
d) All of the mentioned
Answer: c
Explanation: Steady state stability means to maintain the stable system inside and outside too with the external tie lines.
This set of Power Systems Multiple Choice Questions & Answers focuses on “One-Line Diagram and Impedance or Reactance Diagram”.
1. What is the main purpose of reactance diagram?
a) Load flow analysis
b) Falt analysis
c) Calculation of ratings of Alternators
d) Calculation of ratings of Transformers
Answer: b
Explanation: The main purpose of reactance diagram is fault analysis. Load flow analysis is done by the help of Impedance diagram. All these diagrams are made using symmetrical component analysis method on per phase basis.
2. Which of the following is not neglected during formation of reactance diagram from impedance diagram?
a) Resistance of various power system components
b) Static loads
c) Shunt component of Transformers
d) Reactance of alternators
Answer: d
Explanation: Reactance diagram is drawn by the help of symmetrical network of various power system components by neglecting resistance of various components, static loads like induction motors and shunt component of Transformers.
3. Impedance diagram is used for analysis of __________
a) Load flow
b) Alternator
c) Fault
d) Transmission Line
Answer: a
Explanation: Impidance diagram is made for the analysis of load flow. Fault analysis is doen by the help of reactance diagram. All these diagrams are made using symmetrical component analysis method on per phase basis.
4. Reactance diagram contains which of the following ?
a) Resistance of Alternator
b) Resistance of transformer winding
c) Induction motor’s equivalent corcuit
d) Inductive reactance of transmission lines
Answer: d
Explanation: Reactance diagram contains only reactance of synchronous machines, transmission line and Transformers. Static loads like induction motors are neglected in diagram.
5. Single line diagram does not represents:
a) Star connection of transformer winding
b) Delta connection of transformer winding
c) Neutral wire of transmission lines
d) Ratings of machines
Answer: c
Explanation: Single line diagram is a representation of balanced power system on per phase basis with neutral eliminated. Neutral wire is not shown in single line diagram. Winding connections is represented beside the symbol of transformer with its Impidance and rating.
6. Single line diagram of which of the following power system is possible?
a) Power system with LLG fault
b) Power system with LG fault
c) Power system with LL fault
d) Balanced power system
Answer: d
Explanation: Only balanced power system can be represented by a single line diagram. Single line diagram is drawn on per phase basis. A power system with LLG, LG and LL faults becomes unbalanced and can not be represented in per phase basis.
7. In impedance diagram different power system elements are represented by symbols.
a) True
b) False
Answer: b
Explanation: In reactance diagram different power system elements are represented by their symmetrical networks.
8. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA and 230 kV on high voltage side, the transformer reactance referred to the low voltage side will be _______.
a) 15.87 Ω
b) 157.8 Ω
c) 176.33 Ω
d) 17.67 Ω
Answer: a
Explanation: X Ω = Xpu*X b = 0.1*158.87 = 15.87 Ω.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Per Unit System”.
1. A power system network is connected as shown in the figure.
power-systems-questions-answers-per-unit-system-q1
Sd1=15+j5 pu
Sd2=25+j15 pu
Zcable = j0.05pu
|V1|=|V2|=1 pu.
The torue angle for the system will be __________
a) 14.4
b) 22.1
c) 16.2
d) 18.2
Answer: a
Explanation: As the resistance is zero, losses will be zero.
PG1=PD1+PD2=40 pu
For the equal sharing of load at the station
PG1=PG2=20pu
Real power flow from bus 1 to 2
power-systems-questions-answers-per-unit-system-q1-exp
2. A single phase distributor of 1 km long has resistance and reactance per conductor of 0.1Ω and 0.15 Ωrespectively. If the far end voltage Vb=200V and current is at 100A at 0.8 lag. At the midpoint a current of 100A is tapped at a pf of 0.6 pf with ref to voltage Vm at mid point. The voltage magnitude at M is ________
a) 218V
b) 200V
c) 232V
d) 220V
Answer: a
Explanation: Drop in MB= ʟ= 18.027ʟ19.44
V M = 200+18.027 = 218.027 V.
3. A single phase motor is connected to 400V, 50Hz supply. The motor draws a current of 31.7A at a power factor 0.7 lag. The capacitance required in parallel with motor to raise the power factor of 0.9 lag is __________
a) 94.62
b) 282.81
c) 108.24
d) 46.87
Answer: a
Explanation: Active power drawn by the motor=VIcosФ = 400*31.7*0.7 = 8876 W
Reactive power = VIsinФ=400*31.7*sin = 9055.3 VAR
New power factor=cosθ2 = 0.9
θ 2 =cos -1
Q2=8876*tan = 4298.855 VAR
Change in reactive power=9055.3-4298.855 = 4756.4 VAR
Qc = V 2 /Xc = V 2 *2πfC
C=4756.4/ = 94.62μF.
4. A single phase motor is connected to 400V, 50Hz supply. The motor draws a current of 31.7A at a power factor 0.7 lag. The additional reactive power to be supplied by the capacitor bank will be ___________
a) 4756
b) 4873
c) 4299
d) 9055.3
Answer: a
Explanation: Active power drawn by the motor=VIcosФ = 400*31.7*0.7 = 8876 W
Reactive power = VIsinФ=400*31.7*sin = 9055.3 VAR
New power factor=cosθ2 = 0.9
θ2=cos-1
Q2=8876*tan = 4298.855 VAR
Change in reactive power=9055.3-4298.855 = 4756.4 VAR.
5. A 275 kV TL has following line constants A=0.85ʟ5o, B=200ʟ75o. The active power received if the voltage to be maintained is 275kV will be __________
a) 117.63
b) 220
c) 120
d) 115.25
Answer: a
Explanation: |Vs|=|Vr|=275 kV
power-systems-questions-answers-per-unit-system-q5
6. A 275 kV TL has following line constants A=0.85ʟ5o, B=200ʟ75o. The active power angle such that the voltage to be maintained at the other end will be 275 kV ____________
a) 22
b) 16
c) 18
d) 24
Answer: a
Explanation: |Vs|=|Vr|=275 kV
α= 5 o , β= 75 o
power-systems-questions-answers-per-unit-system-q6
7. A power system has a maximum load of 15 MW. Annual load factor is 50%. The reserve capacity of plant is _____ if the plant capacity factor is 40%.
a) 3.75 MW
b) 4.75 MW
c) 18.75 MW
d) 5.75 MW
Answer: a
Explanation: LF = /=0.5
Plant capacity factor =/= 0.5/0.4
Plant capacity= *15 = 18.75 MW
Reserve Capacity = 18.75-15 = 3.75 MW.
8. A 100 MVA synchronous generator operates on full load at a frequency of 50 Hz. The load is suddenly reduced to 50 MW. Due to time lag in governor system, the steam valve begins to close after 0.4s. The change in the frequency is ________.
a) 1
b) 0.5
c) -1.5
d) 0.8
Answer: a
Explanation: Energy transferred in 0.4 sec = 50*0.4= 20 J
power-systems-questions-answers-per-unit-system-q8
9. A 50 Hz four pole turbo-generator rated 100 MVA, 11 kV has an inertia constant of 8 MJ/MVA. If the mechanical input is suddenly raised to 80 MW for an electrical load of 50MW, then the rotor acceleration is ____________
a) 337.5
b) 3.375
c) 457.5
d) 4.57
Answer: a
Explanation: Energy stored = 100*8 =800MJ
Accelerating power = Md 2 δ/dt 2
M=GH/180f = 800/ = 4/45 MJs/elect. Deg
power-systems-questions-answers-per-unit-system-q9
10. A single phase TL has copper conductor of 0.775 cm2 cross section through which 200 kW at UPF at 330 V is to be maintained. If the efficiency of transmission line is 90%, then the minimum length of TL is ___________.
a) 13.6 km
b) 14 km
c) 136 km
d) 16.4 km
Answer: a
Explanation: Pr=200 kW, efficiency=0.9
Ps= 200/0.9=222.22 kW
Losses=22.22 kW
Current, I=200000/3300 = 60.60 A
Line losses=2I 2 R
R=22.22/=3.02 Ω
R=ρl/a
Length, l = / = 13.6 km.
11. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA and 230 kV on high voltage side, the reactance of transformer in per units is __________
a) 0.1
b) 0.3
c) 0.03
d) 1.5
Answer: a
Explanation: The pu value of a transformer does not change.
12. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA and 230 kV on high voltage side, the high voltage side impedance ____________
a) 1763.3 Ω
b) 158.7 Ω
c) 15.87 Ω
d) 176.3 Ω
Answer: a
Explanation: On the high voltage side, Zb=kVb2/MVAb = 2302/30 = 1763.33 Ω.
13. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA and 230 kV on high voltage side, the low voltage side impedance is ___________
a) 158.7 Ω
b) 176.3 Ω
c) 1763.3 Ω
d) 15.87 Ω
Answer: a
Explanation: On the low voltage side, Zb=kV b 2 /MVA b =692/30 = 158.7 Ω.
14. A three phase transformer has a nameplate rating of 30 MVA, 230Y/69Y kV with a leakage -reactance of 10% and the transformer connection is wye-wye. Choosing a base of 30MVA and 230 kV on high voltage side, the transformer reactance referred to the high voltage side will be _________.
a) 176.33 Ω
b) 17.67 Ω
c) 158.7 Ω
d) 15.87 Ω
Answer: a
Explanation: Zb=kVb 2 /MVA b = 2302/30 = 1763.33 Ω
X Ω = Xpu*X b = 0.1*1763.33 = 176.33 Ω.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Short Transmission Line – 1”.
1. Which of the following transmission line can be considered as short transmission line?
a) Transmission line of length upto 600 Km
b) Transmission line of length upto 500 Km
c) Transmission line of length upto 200 Km
d) Transmission line of length upto 80 Km
Answer: d
Explanation: The transmission lines having length less than 80 Km are considered as short transmission lines.Their operating voltage is also less than medium and long transmission lines.
2. Which of the following is correct operating voltage range for short transmission lines.
a) Less than 456 KV
b) Less than 132 KV
c) Less than 20 KV
d) Less than 100 KV
Answer: c
Explanation: Transmission lines having length lesser than 80 Km and operating voltage lower than 20 KV fall in the category of short transmission lines.
3. What is the line to earth capacitance value of the short transmission line.
a) Very high
b) Medium
c) Low
d) Negligible
Answer: d
Explanation: Due to smaller distance and lower line voltage, the capacitance effects are extremely small and, so are neglected.
4. Performance of short transmission lines depends on which of the following?
a) Resistance and Capacitance
b) Resistance and Inductance
c) Inductance and Capacitance
d) Resistance, Inductance and Capacitance
Answer: b
Explanation: Due to smaller distance and lower line voltage, the capacitance effects are extremely small and, so are neglected. So, performance of short transmission lines depends only on inductance and resistance of the line.
5. Performance analysis of short transmission line is done __________
a) By symmetrical component analysis method
b) By reactance diagram
c) On per phase basis
d) By neglecting line inductance
Answer: c
Explanation: Performance analysis of balance transmission line is done only. And is done on per phase basis. No symmetrical component method or reactance diagram method is required for performance analysis.
6. What is the value of shunt conductance of short transmission line?
a) Very high
b) Medium
c) Low
d) Negligable
Answer: d
Explanation: In short transmission lines the shunt conductance and shunt capacitance are neglected and so only series resistance and inductance are to be considered.
7. In short transmission line the reciving end voltage may be greater than sending end voltage due to Ferranti effect.
a) True
b) False
Answer: b
Explanation: Ferranti effect is caused due to the high capacitance of the transmission lines. In short transmission lines capacitance effects are negligible. So, Ferranti effect doesn’t happens in short transmission lines.
8. Series inductance and series resistance of short transmission lines are taken as ___________
a) Lumped and Distributed
b) Distributed and Lumped
c) Both Lumped
d) Both Distributed
Answer: c
Explanation: The series inductance and resistance of short transmission lines are taken as lumped. This makes the performance analysis easy.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Short Transmission Line – 2”.
1. What is the value of charging current in short transmission lines?
a) Less than medium transmission lines
b) Equal to medium transmission lines
c) More than medium transmission lines
d) More than long transmission lines
Answer: c
Explanation: Line to Earth capacitance of short transmission line is less than that in medium and long transmission line and is negligable. Because of this the charging current of short transmission line is less than that in medium and long transmission line and is negligable.
2. What is the value of Inductive reactance in short transmission lines?
a) More at reciving end
b) More at sending end
c) Uniformly distributed over entire length
d) More in middle of sending end and reciving end
Answer: c
Explanation: Actually the inductive reactance of line is uniformly distributed over its entire length. To make calculations simple this reactance is assumed to be lumped and connected in series with the line.
3. Regulation of short transmission lines depends:
a) Only on line resistance
b) Only on line inductance
c) Only on line capacitance
d) On line inductance and line resistance
Answer: d
Explanation: The expression of voltage regulation of short transmission line shows that, its voltage regulation depends on line resistance and line inductive reactance. Capacitance of short transmission line is negligible so it does not cause its effecting it.
4. What is the percentage voltage regulation of short transmission line if its sending end and reciving end voltages are 160 KV and 132 KV respectively?
a) 30 %
b) 21.21 %
c) 12.12 %
d) 38.22 %
Answer: b
Explanation: % Voltage Regulation = ÷ Reciving end voltage
= [ × 100] ÷ 132
= 21.21 %.
5. A single phase transmission line is transmitting 1,100 KW power at 11 KV and at unity power fector. If it has a total resistance of 5 Ω, what is the efficiency of the transmission line?
a) 80 %
b) 89.65 %
c) 97.24 %
d) 99.54 %
Answer: c
Explanation: Efficiency = Power delivered ÷
Line current = P/V
=
= 100 Amp.
Line losses = I2 R
= 2 5
= 50 KW
η = [11000/] × 100
= 99.54 %.
6. Voltage regulation of a transmission line should be ________
a) Minimum
b) Maximum
c) Greater than 50 %
d) Less than 50 %
Answer: a
Explanation: More value of voltage regulation means more voltage fluctuations and this is undesirable. So the value of voltage regulation should be as low as possible.
7. Which of the following is like equivalent circuit of short transmission line?
a) Series RLC circuit
b) Parallel RLC circuit
c) Series RL circuit
d) Parallel RL circuit
Answer: c
Explanation: Due to smaller distance and lower line voltage, the shunt capacitance effects are extremely small and also the shunt conductance effects are very low. So both of them are neglected and equivalent circuit contains only series inductance and resistance.
8. In single phase transmission lines resistance and inductance are considered only up to neutral.
a) True
b) False
Answer: b
Explanation: In case of single phase transmission lines the total loop resistance and inductance is to be taken into account. Resistance and inductance only up to neutral are taken into account for 3 phase transmission lines.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Medium Transmission Line – 1”.
1. Which of the following transmission line can be considered as medium transmission line?
a) Transmission line of length upto 600 Km
b) Transmission line of length upto 500 Km
c) Transmission line of length upto 200 Km
d) Transmission line of length upto 80 Km
Answer: c
Explanation: The transmission lines having length more than 80 Km and less than 200 Km are considered as medium transmission lines.Their operating voltage is more than short transmission lines but less than long transmission lines.
2. Which of the following is correct operating voltage range for medium transmission lines.
a) More than 765 KV
b) More than 400 KV
c) More than 20 KV
d) More than 132 KV
Answer: c
Explanation: Transmission lines having length more than 80 Km and less than 200 Km, operating voltage between 20 KV and 100 KV fall in the category of medium transmission lines.
3. What is the value of the charging current flowing to earth in medium transmission line.
a) Very high
b) Medium
c) Negligible
d) No capacitance
Answer: b
Explanation: Owing to appreciable length and voltage of the line the charging current is appreciable in medium transmission lines. Also the capacitance effect cannot be ignored in medium transmission lines.
4. Performance of short transmission lines depends on which of the following?
a) Resistance and Capacitance
b) Resistance and Inductance
c) Inductance and Capacitance
d) Resistance, Inductance and Capacitance
Answer: d
Explanation: Medium transmission lines have enough value of resistance and inductance. Length and operating voltage of the medium transmission lines are sufficiently large to cause unavoidable charging current and therefore capacitance effect can not be ignored. Hence, performance of Medium transmission lines depends on R, L and C.
5. Performance analysis of medium transmission line is done ________
a) By reactance diagram
b) By symmetrical component analysis method
c) By neglecting line inductance
d) On per phase basis
Answer: d
Explanation: Performance analysis of balance transmission line is done only. And is done on per phase basis. No symmetrical component method or reactance diagram method is required for performance analysis.
6. What is the value of shunt capacitance of medium transmission line?
a) Very high
b) Medium
c) Zero
d) Negligable
Answer: b
Explanation: Length and operating voltage of the medium transmission lines are sufficiently large to cause unavoidable charging current and therefore capacitance effect can not be ignored. Capacitance effect in medium transmission line is less than that in long transmission line.
7. In medium transmission line the reciving end voltage may be greater than sending end voltage due to Ferranti effect.
a) True
b) False
Answer: a
Explanation: Ferranti effect happens when capacitance effect in medium or long transmission lines becomes greater than inductance effect. This happens during low or no load period.
8. Series inductance and series resistance of medium transmission lines are taken as:
a) Distributed and Lumped
b) Lumped and Distributed
c) Distributed
d) Lumped
Answer: d
Explanation: The series inductance and resistance of medium transmission lines are taken as lumped. This makes the performance analysis easier.
9. Which of the following is like equivalent circuit of medium transmission line?
a) Series RLC circuit
b) RLC circuit in pie form
c) Series RL circuit
d) Parallel RL circuit
Answer: b
Explanation: Medium transmission lines have considerable amount of inductance, resistance and shunt capacitance. Medium transmission lines are represented as either pie form or as T form.
10. In medium transmission lines shunt capacitances are considered as lumped.
a) true
b) false
Answer: a
Explanation: In case of medium transmission lines the charging current is unavoidable but less than that in long transmission lines. So it does not cause much error in calculations if shunt capacitances are taken as lumped.
This set of Power Systems online test focuses on “Medium Transmission Line – 2”.
1. In medium transmission lines capacitive current is ________________
a) Less than short transmission lines
b) Equal to short transmission lines
c) More than short transmission lines
d) More than long transmission lines
Answer: c
Explanation: Line to Earth capacitance of medium transmission line is more than that in short transmission line and less than that in long transmission line. Because of this the charging current of medium transmission line is more than that in short transmission line and less than that in long transmission line.
2. In actual the capacitance of line is ____________
a) More at receiving end
b) More at sending end
c) Uniformly distributed over entire length
d) More in middle of sending end and receiving end
Answer: c
Explanation: Actually the capacitance of line is uniformly distributed over its entire length. To make calculations simple the capacitance of the system is assumed to be divided up and lumped in the form of capacitors shunted across the line at one or more points.
3. Charging current in medium transmission line is _________________
a) Maximum at receiving end
b) Maximum at sending end
c) More in between sending and receiving end
d) Equal throughout the line
Answer: a
Explanation: The magnitude of capacitive current flowing at any point along the line is that required to charge the section of the line between the given point and receiving end. Hence, it has maximum value at the sending in and diminished at practically uniform rate down to zero at the receiving end.
4. In end condenser method of solution of medium transmission line, capacitance of the line is assumed to be _____________
a) Distributed uniformly from sending end to receiving end
b) Lumped at the load end
c) Lumped at the generation end
d) Lumped at middle of generation and load end
Answer: b
Explanation: In end condenser method the capacitance of the line is assumed to be lumped at the load end. This method overestimates the effect of capacitance.
5. In nominal-T method of solution of medium transmission line, capacitance is assumed to be __________
a) Distributed uniformly from sending end to receiving end
b) Lumped at the load end
c) Lumped at the generation end
d) Lumped at middle of generation and load end
Answer: d
Explanation: In nominal- T method or middle condenser method of analysis of medium transmission line the whole of the line capacitance is assumed to be concentrated at the middle point of the line and half the line resistance and reactance to be lamp on either side.
6. In nominal-π method of solution of medium transmission line, capacitance is assumed to be:
a) Distributed uniformly from sending end to receiving end
b) Divided into two halves
c) Lumped at the generation end
d) Lumped at middle of generation and load end
Answer: b
Explanation: In nominal-π method of solution of medium transmission line the capacitance of each line conductor is assumed to be divided into two halves. One half being shunted between line conductor and neutral at the receiving in and other half at the sending end.
7. Medium transmission line operates below voltage level of 20 KV.
a) True
b) False
Answer: b
Explanation: The voltage limit of 20 KV is for short transmission lines. Medium transmission lines can operate for voltage more than 20 KV.
8. Which of the following is not a method for solution of medium transmission line?
a) End condenser method
b) Nominal-T method
c) Nominal-π method
d) Nominal-H method
Answer: d
Explanation: Actual method used for solution of medium transmission lines are end condenser method, nominal-T method and nominal π method.
9. In a nominal-π method the resistance of line is assumed to be __________
a) Distributed uniformly from sending end to receiving end
b) Divided into two halves
c) Lumped at the generation end
d) Lumped at middle of the line
Answer: d
Explanation: In nominal-π method the capacitance of each line conductor is assumed to be divided into two halves and the resistance of the line is assumed to be lumped in between them at the middle of the line.
10. In nominal-T method of solution of medium transmission line, resistance and inductive reactance of the line is divided into two half’s.
a) True
b) False
Answer: a
Explanation: In nominal-T method of solution of medium transmission line, the whole of the line capacitance is assumed to be concentrated at the middle point of the line and half the line resistance and reactance to be lumped on either side of it.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Long Transmission Line”.
1. Length of long transmission line is more than ___________
a) 80 Km
b) 50 Km
c) 120 Km
d) 200 Km
Answer: d
Explanation: Transmission lines having length more than 200 kilometres are categorised as long transmission lines. Transmission lines having length less than 200 kilometres are medium transmission lines.
2. In long transmission lines Resistance and Capacitance parameters of lines are connected in __________
a) Series, shunt
b) Series, series
c) Shunt, shunt
d) Shunt, parallel
Answer: d
Explanation: The resistance and inductance parameters are series elements of long transmission line. Capacitive susceptance and conductance parameters are shunt elements of transmission lines.
3. Range of surge impedance for an overhead transmission line is ____________
a) 12 Ω – 144 Ω
b) 40 Ω – 60 Ω
c) 400 Ω – 600 Ω
d) 300 Ω – 900 Ω
Answer: c
Explanation: Surge impedance is the characteristic impedance of a loss free transmission line. It is the square root of ratio of line impedance and shunt admittance . Its value varies between 400 Ω and 600 Ω.
4. Range of surge impedance for an underground cables is _____________
a) 12 Ω – 144 Ω
b) 40 Ω – 60 Ω
c) 400 Ω – 600 Ω
d) 300 Ω – 900 Ω
Answer: b
Explanation: Surge impedance is the characteristic impedance of a loss free transmission line. It is the square root of ratio of line impedance and shunt admittance . Its value varies between 40 Ω and 60 Ω.
5. Synchronous phase modifiers are installed at which of the following position of the transmission line?
a) Reciving end
b) Sending end
c) Between reciving end and sending end
d) Near reciving end
Answer: b
Explanation: For constant voltage transmission, specially designed synchronous motors, called synchronous phase modifiers. Synchronous phase modifiers are installed at receiving end to maintain the voltage drop along the line constant.
6. The voltage rating of long transmission line is _________
a) 20 KV to 100 KV
b) Upto 20 KV
c) Above 100 KV
d) 60 KV to 80 KV
Answer: c
Explanation: The transmission line having length above time 200 kilometre and line voltage above 100 KV fall into the category of long transmission line.
7. The shunt capacitive susceptance in long transmission line is greater than that in medium and short transmission line.
a) True
b) False
Answer: a
Explanation: Due to long length and high voltage of line the charging current is very high for the long transmission line and therefore the capacitance in long transmission line is also very high and is more than that in short and medium transmission line.
8. What is the value of characteristics impedance for loss free transmission line?
a) √
b) √
c) √
d) √
Answer: a
Explanation: Characteristic impedance of a long transmission line is given by
Zc = √[ / ] For loss less transmission line resiatance and shunt conductance are equal to zero. And hence, Z0 is given by
Z0 = √.
9. The leakage current through the shunt admittance is __________
a) Maximum at sending end
b) Maximum at receiving end
c) Uniform over length of line
d) Maximum at centre of line
Answer: a
Explanation: The leakage current through the shunt admittance is maximum at the sending end of the transmission line. This current decreases continuously as it move towards the receiving end of the line and becomes zero at the receiving end.
10. Value of leakage current at reciving end of transmission line is zero.
a) True
b) False
Answer: a
Explanation: Value of leakage current through the shunt admittance is maximum at the sending end of the transmission line. This current decreases continuously as we move towards the receiving end of the line and becomes zero at the receiving end.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Ferranti Effect & Methods of Voltage Control”.
1. Ferranti effect is not a problem for ________
a) Long Transmission lines
b) Medium Transmission lines
c) Short Transmission lines
d) Transmission line having high capacitance
Answer: c
Explanation: Ferranti effect is happens when line to earth capacitance becomes more than the inductance parameter. This effect is more predominant in medium and long transmission lines but is not a problem for short transmission lines. This is because line to earth capacitance for short transmission line is negligible.
2. What happens during the Ferranti effect?
a) Reciving end current becomes more than sending end current
b) Reciving end voltage becomes more than sending end voltage
c) Reciving end power becomes more than sending end power
d) Reciving end frequency becomes more than sending end frequency
Answer: b
Explanation: In a medium or long transmission line when open circuited or lightly loaded the receiving end voltage is found more than the standing in voltage. This phenomenon of rise in voltage at receiving end of open circuited or lightly loaded line is called Ferranti effect.
3. During Ferranti effect the voltage drop across line resistance ___________
a) In phase with reciving end voltage
b) lags behind reciving end voltage
c) lead the reciving end voltage
d) lags behind sending end voltage
Answer: c
Explanation: During Ferranti effect the leading charging current is more than lagging component of current. Net line current leads the sending end and reciving end voltage. Hence the iR drop leads these voltages.
4. A transmission line of 200 Km is supplying at 50Hz frequency. What is the percentage rise in voltage at reciving end?
a) 20%
b) 1.2%
c) 2.19%
d) 20.8%
Answer: c
Explanation: Percentage rise in voltage = /18
Solving this % V rise = { × 2002 × 10-8}/18
= 2.19%.
5. Which of the following equipment or element can reduce Ferranti effect?
a) Relay
b) Circuit Breaker
c) Resistors
d) Current limiting reactors
Answer: d
Explanation: For high voltage and extra high voltage lines shunt reactors are provided to absorb part of charging current. As leading charging current is reduced. Ferranti effect is also reduced.
6. Under no load condition inductance of line predominant the line to earth capacitances.
a) True
b) False
Answer: b
Explanation: Under no load condition capacitance between line and earth predominant the inductance of long and medium transmission lines.
7. What is the limit within which the consumer’s end terminal voltage should be maintained?
a) ± 9 %
b) ± 10 %
c) ± 5 %
d) ± 6 %
Answer: d
Explanation: The voltage fluctuations at consumers end may cause malfunction or event damage of consumer’s equipments. So, the voltage at the consumers end must be maintained within prescribed limit upto ± 6% of declared supply voltage so that the consumers apparatus may operate satisfactorily.
8. What is the main reason for maintaining consumer end voltage within prescribed limit?
a) Because it is declared by the supplier
b) For satisfactory operation of electrical equipments
c) For easy calculation of units supplied
d) To reduce the line losses
Answer: b
Explanation: All electrical equipments are designed to work at a certain voltage mentioned as voltage rating of that equipment. Change of supply voltage beyond a certain limit may cause malfunction or even damage to the equipment. So, the consumer end voltage must be maintained to a prescribed limit for satisfactory operation of consumer’s equipments.
9. Which of the following equipment is not used for voltage control?
a) Tap changing transformer
b) Induction generators
c) Series compensators
d) Synchronous phase modifiers
Answer: b
Explanation: Induction generators are not used for voltage control. Tap changing transformer is used to control distribution end voltage for upto limited voltage variations. Series compensators and Synchronous phase modifiers controls line voltage by supplying required leading or lagging VAR.
10. What is the full form of AVR? This term is related to voltage control?
a) Automatic Voltage Rectifier
b) Actuated Voltage Rectifier
c) Automatic Voltage Rectifier
d) Automatic Voltage Regulator
Answer: d
Explanation: AVR stands for Automatic Voltage Regulator. It operates on the principle of detection of error and is used to control the line voltage.
11. On which side of the transformer tap changer is provided?
a) On High Voltage side
b) On low voltage side
c) On high voltage and low voltage side
d) In core
Answer: a
Explanation: In tap changing transformer there is always a typing on the high voltage winding which when connected to the rated voltage gives rated voltage on the low voltage side. This tapping is called principal typing.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Short Circuit of a Synchronous Machine ”.
1. Transient in synchronous generator is similar to which of the following circuit?
a) Parallel RLC circuit
b) Series RLC circuit
c) Series RL circuit
d) Parallel RL circuit
Answer: c
Explanation: The current flowing in armature of synchronous generator when its terminals are short circuited is similar to that flowing when sinusoidal voltage is suddenly applied to an RL series circuit.
2. When all three phases of a synchronous generator on no load are suddenly short circuited then symmetry of the short circuit current depends on which of the following?
a) Position of fault
b) Symmetry of fault
c) Instantaneous Voltage at which fault occurs
d) Resistance of armature winding
Answer: c
Explanation: Symmetry of the short circuit current about time axis and DC offset depends upon the value of phase voltage at which short circuit occurs.
3. In a synchronous generator for how much time subtransient period of symmetrical short circuit current lasts?
a) For 200 Cycles
b) For 500 Cycles
c) For 30 Cycles
d) For 2 Cycles
Answer: d
Explanation: Subtransient period lasts for only about 2 cycles. During this period the subtransient current decay is very rapidly.
4. In a synchronous generator for how much time transient period of symmetrical short circuit current lasts?
a) For 200 Cycles
b) For 500 Cycles
c) For 30 Cycles
d) For 2 Cycles
Answer: c
Explanation: In a synchronous generator transient period of symmetrical short circuit current lasts for about 30 cycles. During this period current decreases somewhat slower than the current in subtransient period.
5. After how many cycles in a synchronous generator symmetrical short circuit current reaches to its steady state value?
a) After 200 Cycles
b) After 500 Cycles
c) After 30 Cycles
d) After 2 Cycles
Answer: c
Explanation: In a synchronous generator subtransient period of short circuit current lasts for up to 2 cycles the transient period of that lies for about 30 cycles. After that the current reaches to its steady state value.
6. What is the phase current in phase Y and in phase B out of R-Y-B when sudden short circuit to all three phases occurs at no load? It is given that after fault current in phase R is equal
a) Y = V m Sin & B = V m Sin
b) Y = V m Sin & B = V m Sin
c) Y = V m Sin & B = V m Sin
d) Y = V m Sin & B = V m Sin
Answer: b
Explanation: The given phase sequence is R-Y-B . When all three phases are short circuited then the fault is symmetrical that means fault current flowing through each phases will be 120° apart from each other.
7. In case of synchronous generator the reactants is constant.
a) True
b) False
Answer: b
Explanation: In case of synchronous generator the reactance is not a constant one but is a function of time. The reactance of synchronous generator is different for subtransient state, transient state and steady state.
8. If X l is leakage reactance, X f is reactance due to field winding, X dw is reactance due to damper winding and X a is armature winding reactance then reactance of synchronous generator in subtransient state is due to which of the following?
a) X l ,X dw and X a
b) X l and X a
c) X l , X f ,X dw and X a
d) X l and X dw
Answer: c
Explanation: During the initial part of short circuit or during subtransient period equivalent circuit of alternator contains the field winding reactance damper winding reactance armature winding reactance in parallel and leakage reactance in series.
9. Which of the following reactance is eliminated first in synchronous generator just after the symmetrical fault?
a) Leakage reactance
b) Damper winding reactance
c) Armature winding reactance
d) Field winding reactance
Answer: b
Explanation: As the damper winding currents are first to die out, damper winding reactance effectively becomes open circuited. After that Approximate circuit model of synchronous generator contains only leakage reactance, field winding reactance and armature winding reactance.
10. Steady state direct axis reactance is greater than subtransient direct axis reactance and transient direct axis reactance.
a) True
b) False
Answer: a
Explanation: During transient and subtransient period the armature winding reactance contains other reactances like damper winding reactance and field winding reactances in parallel with it. So, the net reactance during subtransient and transient period are less than the net reactance during steady state period.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Symmetrical Component Transformation – 1”.
1. The receiving end active power for a short transmission line is
power-systems-questions-answers-symmetrical-component-transformation-1-q1
Answer: a
Explanation: Receiving end active power for a short transmission line is
power-systems-questions-answers-symmetrical-component-transformation-1-q1a
2. The receiving end reactive power for a short transmission line is
power-systems-questions-answers-symmetrical-component-transformation-1-q1
Answer: c
Explanation: Receiving end reactive power for a short transmission line is
power-systems-questions-answers-symmetrical-component-transformation-1-q2
3. The sending end active power for a 20 km transmission line with Vs as the sending end voltage and Vr as receiving end voltage, can be given by most appropriately
power-systems-questions-answers-symmetrical-component-transformation-1-q3
Answer: a
Explanation: The sending end active power is power-systems-questions-answers-symmetrical-component-transformation-1-q3a
4. The sending end reactive power for a 20 km transmission line with Vs as the sending end voltage and Vr as receiving end voltage, can be given by most appropriately
power-systems-questions-answers-symmetrical-component-transformation-1-q3
Answer: d
Explanation: The sending end reactive power is power-systems-questions-answers-symmetrical-component-transformation-1-q4
5. The simplified ABCD representation of a 40 km transmission line is best given as
power-systems-questions-answers-symmetrical-component-transformation-1-q5
Answer: a
Explanation: From the given length, it is a short TL. Hence,
power-systems-questions-answers-symmetrical-component-transformation-1-q5a
6. For a 35 km transmission line having a lumped impedance of the line as 20 ohms, is required to be shown in the ABCD form, it is given as
power-systems-questions-answers-symmetrical-component-transformation-1-q6
Answer: a
Explanation: From the given length, it is a short TL. Hence,
power-systems-questions-answers-symmetrical-component-transformation-1-q6a
7. If it is tried to represent the active and reactive power on a circle, then the radius would be
power-systems-questions-answers-symmetrical-component-transformation-1-q7
Answer: a
Explanation: power-systems-questions-answers-symmetrical-component-transformation-1-q7a
8. The maximum power delivered to the load for short transmission line is at
a) β=α
b) β>α
c) β=δ
d) β>δ
Answer: c
Explanation: Maximum power occurs for β=δ.
9. The maximum real active power delivered to the load is defined most accurately by
power-systems-questions-answers-symmetrical-component-transformation-1-q9
Answer: a
Explanation: The maximum real active power delivered to the load is power-systems-questions-answers-symmetrical-component-transformation-1-q9a
10. For a given power system, its zero and maximum regulation will occur at the impedance angle of
a) 45
b) 90
c) 0
d) 60
Answer: a
Explanation: At θ=45°, ZVR and maximum VR coincide.
11. The charging currents due to shunt admittance can be neglected for ______ transmission line?
a) short
b) long
c) medium
d) all of the mentioned
Answer: a
Explanation: The shun admittance for lines more than 100 km become very prominent and can not be neglected.
12. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify the missing term marked as ’?’.
V s = ?*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-symmetrical-component-transformation-1-q12
a) 1+YZ
b) Z
c) Y
d) 1
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
13. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify the missing term marked as ’?’.
V s = A*V r +?*I r
I s = C*V r +D*I r
power-systems-questions-answers-symmetrical-component-transformation-1-q12
a) 1+YZ
b) Z
c) Y
d) 1
Answer: b
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
14. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify the missing term marked as ’?’.
V s = A*V r +B*I r
I s = ?*V r +D*I r
power-systems-questions-answers-symmetrical-component-transformation-1-q12
a) 1+YZ
b) Z
c) Y
d) 1
Answer: c
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
15. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify the missing term marked as ’?’.
V s = A*V r +B*I r
I s = C*V r +?*I r
power-systems-questions-answers-symmetrical-component-transformation-1-q12
a) 1+YZ
b) Z
c) Y
d) 1
Answer: d
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
This set of Power Systems online quiz focuses on “Symmetrical Component Transformation – 2”.
1. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) 1+YZ, Z
b) Z,Y
c) Y, 1+YZ
d) 1+YZ, Y -1 +Z
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
2. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and C parameters.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) 1+YZ, Z
b) Z,Y
c) 1+YZ, Y
d) 1+YZ, Y -1 +Z
Answer: c
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
3. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and D parameters.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) 1+YZ, 1
b) 1+YZ, Z
c) Y, 1+YZ
d) 1+YZ, Y -1 +Z
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
4. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify B and A parameters.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) 1+YZ, Z
b) Z,YZ+1
c) Z, 1+YZ
d) 1+YZ, Y -1 +Z
Answer: b
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
5. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify C and A parameters.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) 1+YZ, Z
b) Z,Y
c) Y, 1+YZ
d) 1+YZ, Y -1 +Z
Answer: c
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
6. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify D and A parameters.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) 1+YZ, Z
b) 1+ZY, 1
c) Y, 1+YZ
d) 1, 1+YZ
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
7. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find AB value.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) * Z
b) 1+YZ* Z
c) Y*
d) *Y -1 +Z
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
8. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘A*C’ value.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) * Y
b) * Z
c) Y*
d) *Y -1 +Z
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r .
9. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘A*D’ value.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a)
b) * Z
c) 1
d) 0
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r + Z*I r
I s = Y*V r + I r
AD = .
10. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘B*D’ value.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a)
b) * Z
c) Z
d) YZ
Answer: c
Explanation: Using KVL to the line diagram,
V s = *V r + Z*I r
I s = Y*V r + I r
BD = Z.
11. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘B*C’ value.
V s = A*V r + B*I r
I s = C*V r + D*I r
power-systems-questions-answers-online-quiz-q1
a)
b) * Z
c) 1
d) YZ
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r
BC = YZ.
12. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘C*D’ value.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a)
b) * Z
c) Z
d) Y
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r
CD = Y*1 = Y.
13. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘AB-CD’ value.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) Z-Y+YZ 2
b) * Z
c) 1+YZ+YZ 2
d) 1-YZ+ZY 2
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r
AB-CD = *Z-Y.
14. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘AD-BC’ value.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) Z-Y+YZ 2
b) * Z
c) YZ+YZ 2
d) 1
Answer: d
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r
AD-BC = -YZ = 1.
15. The transmission line equations are given by the below set of equations based on the line diagram as given. Identify A and B parameters and find ‘A*C*D’ value.
V s = A*V r +B*I r
I s = C*V r +D*I r
power-systems-questions-answers-online-quiz-q1
a) ZY+ 2
b) * Z
c) YZ+YZ 2
d) 1-YZ+ZY 2
Answer: a
Explanation: Using KVL to the line diagram,
V s = *V r +Z*I r
I s = Y*V r +I r
ACD = *ZY.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Comparison of Faults in Three Phase System – 1”.
1. A three phase transformer has a name plate details of 30 MVA and voltage rating of 230Y kV/69∆ kV with a leakage reactance of 10% and the transformer connection via wye-delta. Taking a base of 230 kV on the high voltage side, turns ratio of the windings is ______
a) 2
b) 1.5
c) 6
d) 4
Answer: a
Explanation: n= V HV /V LV = /69=1.9245.
2. A three phase transformer has a name plate details of 30 MVA and voltage rating of 230Y kV/69∆ kV with a leakage reactance of 10% and the transformer connection via wye-delta. Taking a base of 230 kV on the high voltage side, the transformer reactance on the LV side is
___________
a) 176.33 Ω
b) 1763.3 Ω
c) 47.6 Ω
d) 15.87 Ω
Answer: a
Explanation: Zb = kV b ) 2 /MVA b
Zb = 230 2 /30=1763.33 Ω
XΩ =0.1*1763.33 = 176.33 Ω.
3. A three phase transformer has a name plate details of 30 MVA and voltage rating of 230Y kV/69∆ kV with a leakage reactance of 10% and the transformer connection via wye-delta. Taking a base of 230 kV on the high voltage side, the transformer reactance referred to the low voltage side in ohms is __________
a) 47.61 Ω
b) 15.87 Ω
c) 176.33 Ω
d) 157.8 Ω
Answer: a
Explanation: Zb = (kV b 2 /MVA b = 230 2 /30=1763.33 Ω
XΩ =0.1*1763.33 = 176.33 Ω
XΩ =176.33/ = 47.61 Ω.
4. A three phase transformer has a name plate details of 30 MVA and voltage rating of 230Y kV/69∆ kV with a leakage reactance of 10% and the transformer connection via wye-delta. Taking a base of 230 kV on the high voltage side, the transformer reactance referred to the low voltage side in ohms is
a) 0.1
b) 0.2
c) 0.198
d) 0.4
Answer: a
Explanation: XΩ = XΩ /n 2
= 176.33/ 2 =15.87 Ω
Xpu= 15.87/158.7 = 0.1.
5. A 200 bus power system has 160 PQ bus. For achieving a load flow solution by N-R in polar coordinates, the minimum number of simultaneous equation to be solved is ___________
a) 359
b) 329
c) 360
d) 320
Answer: a
Explanation: Total buses = 200
PQ buses = 160
PV buses = 200-160 = 40
Slack bus = 1
Total number of equation = *1 + = 359.
6. Two alternators A and B having 5% speed regulation are working in parallel at a station. Alternator A is rated at 15 MW while B is at 20 MW. When the total load to be shared is 12 MW, then how much of the load will be shared by the alternator B?
a) 6.85 MW
b) 5.14 MW
c) 6 MW
d) 7 MW
Answer: a
Explanation: 1 α15 ;
P2 α 20;
power-systems-questions-answers-comparision-faults-three-phase-system-1-q6
P1 = 0.75 P2 …
P1 +P2 = 12 …
Solving above, P2 = 6.85 MW.
7. Two alternators A and B having 5% speed regulation are working in parallel at a station. Alternator A is rated at 15 MW while B is at 20 MW. When the total load to be shared is 12 MW, then how much of the load will be shared by the alternator B?
a) 6.85 MW
b) 5.14 MW
c) 6 MW
d) 7 MW
Answer: a
Explanation: 1 α15 ;
P2 α 20;
power-systems-questions-answers-comparision-faults-three-phase-system-1-q6
P1 = 0.75 P2 …
P1 +P2 = 12 …
Solving above equations, P1 = 5.14 MW.
8. A 400 V, 50 Hz three phase balanced source ripples to a star connected load whose rating is S kVA. The rating of the delta connected capacitor bank needed to bring p.f. to 0.9 lagging is _______ KVAR.
a) 254.7
b) 25.4
c) 84.9
d) 284.5
Answer: a
Explanation: Qc = P[tanθ1 – tanθ2] =300[ – cos -1 0.9] = 254.72 kVAR.
9. A 400 V, 50 Hz three phase balanced source ripples to a star connected load whose rating is S kVA. A delta connected capacitor bank needed to bring p.f. to 0.9 lagging. The operating power factor of the system is
a) 0.8
b) 4/3
c) 3/4
d) 0.6
Answer: a
Explanation: cosФ = 3/5 = 0.6.
10. A given system to be analysed was found with the below phasor representation of the system voltages. Which of the symmetrical components will be present in the mentioned system?
a) Positive sequence components
b) Negative sequence components
c) Zero sequence components
d) All of the mentioned
Answer: a
Explanation: In an unbalanced system, all the symmetrical components will be present.
11. The phasor operator which is used to depict the unbalanced phase voltages into three phase quantities, provides a rotation of
a) 120o counter clockwise
b) 120o clockwise
c) 90o counter clockwise
d) 90o clockwise
Answer: a
Explanation: ‘α’ operator used for the conversion has the counter clockwise rotation of the quantity and it has unity magnititude.
This set of Power Systems Question Bank focuses on “Comparison of Faults in Three Phase System – 2”.
1. The zero sequence depiction of the unbalancing occurring at the terminals of the induction motor will be most likely _____________
a) power-systems-questions-bank-q1
b) power-systems-questions-answers-comparision-faults-three-phase-system-2-q2-b
c) power-systems-questions-answers-comparision-faults-three-phase-system-2-q2-c
d) power-systems-questions-answers-comparision-faults-three-phase-system-2-q2-d
Answer: a
Explanation: The zero sequence components will not have any phase displacement and they are co- phasal in nature.
2. Complete the given phasor diagram by assuming that operator ‘a’ is unity magnitude and counter clockwise rotation of 120 degrees.
power-systems-questions-answers-comparision-faults-three-phase-system-2-q2
a) 1-a
b) a-1
c) 1
d) –a 3
Answer: a
Explanation: Based on the phasor calculations the unknown vector is found using balanced condition of the three vectors A+B+C = 0 and 1+a+a 2 =0. Then the third vector is 1-a.
3. The unknown vector in the given figure is ______ if we assume the system is balanced with a as unity magnitude and counter clockwise rotation of 120 degrees.
power-systems-questions-answers-comparision-faults-three-phase-system-2-q3
a) a
b) 0
c) a 3
d) a 4
Answer: a
Explanation: 1+a+ a 2 = 0.
4. For a balanced three phase system having a vector representation as mentioned in the figure, complete the vector X and Y.
power-systems-questions-answers-comparision-faults-three-phase-system-2-q4
a) X=1-a 2 ; Y=a 2 -a
b) bX=a 2 -a; Y=1-a 2
c) X=a 2 -1; Y=1-a
d) X=a 2 -1; Y=a-1
Answer: a
Explanation: This question can be attempted by using the options. For a balanced system the net voltage will be zero. So option a and b are the shortlisted options. Out of these applying the rotation criteria, option a is the best match.
5. For a balanced three phase system having a vector representation as mentioned in the figure, complete the vector X and Y.
power-systems-questions-answers-comparision-faults-three-phase-system-2-q5
a) X=√3∠30° ; Y = √3∠-90°
b) X=√3∠-30° ; Y = √3∠90°
c) X=√3∠-30° ; Y = √3∠-150°
d) X=√3∠30° ; Y = √3∠150°
Answer: a
Explanation: This question can be attempted by using the options. For a balanced system the net voltage will be zero. So option a and b are the shortlisted options. Out of these applying the rotation criteria, option a is the best match in polar form.
6. The unknown vector in the given figure is ______ if we assume the system is balanced with a as unity magnitude and counter clockwise rotation of 120 degrees.
power-systems-questions-answers-comparision-faults-three-phase-system-2-q6
a) 1∠120°
b) 1∠30°
c) 1∠0°
d) 1∠-120°
Answer: a
Explanation: 1+a+ a 2 = 0; a= 1∠120°.
7. Complete the given phasor diagram by assuming that operator ‘a’ is unity magnitude and counter clockwise rotation of 120 degrees.
power-systems-questions-answers-comparision-faults-three-phase-system-2-q7
a) √3∠-30°
b) √3∠30°
c) √3∠-60°
d) √3∠90°
Answer: a
Explanation: Based on the phasor calculations the unknown vector is found using balanced condition of the three vectors A+B+C = 0 and 1+a+a 2 =0. Then the third vector is 1-a. Converting it in the polar form, it is √3∠-30°.
8. In the cylindrical rotor alternator, the sub transient and negative sequence reactances are same.
a) True
b) False
Answer: a
Explanation: It is true because the saliency offered is zero in the cylindrical pole machines.
9. The zero sequence impedance of a synchronous machine is independent of the pitch of the armature coils.
a) True
b) False
Answer: b
Explanation: The zero sequence impedance does depend on the pitch of the armature coils of the synchronous machine.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Line Compensation – 1”.
1. The instantaneous voltage wave in the long transmission line is a function of _____________
a) time and distance
b) time
c) distance
d) time, distance and reactive inductance
Answer: a
Explanation: It will be a function of time and distance.
2. At any point along the line, the instantaneous voltage is ___________
a) sum of incident and reflected voltage
b) incident voltage
c) sum of incident and refracted voltage
d) twice the incident voltage
Answer: a
Explanation: V = V incident +V refracted .
3. The equation given below is the voltage equation,
power-systems-questions-answers-line-comensation-1-q3
Then it is ________________
a) reflected wave receiving to sending end
b) reflected wave sending to receiving end
c) incident wave from receiving end to sending end
d) refracted wave from receiving end to next end
Answer: a
Explanation: From the equation, cosФ, it is clear that the wave is travelling in left to right and the amplitude is reduced, so it’s a reflected wave.
4. When can an incident wave not distinguish between the termination and an infinite continuation of line?
a) When line is terminated by its characteristic impedance
b) When line is terminated by its surge impedance
c) When line is open
d) When line is terminated by its characteristic and surge impedance
Answer: a
Explanation: The characteristic impedance at the receiving end will cause a confusion for the incident wave.
5. Ferranti effect is more prominent due to ____________
a) line capacitance
b) surge capacitance
c) stray capacitance
d) all of the mentioned
Answer: a
Explanation: Line capacitance causes the no load receiving end voltage to be more than receiving end.
6. The voltage rise happening at the receiving end due to the line charging capacitance has a magnitude of _______________
a) ω 2 CLl 2
b) ω 2 CLl 2 /2
c) ω 2 l 2 /v 2
d) ω 2 CLl 2 and ω 2 l 2 /v 2
Answer: d
Explanation: The circuit diagram for the LTL is
power-systems-questions-answers-line-comensation-1-q6
Is= jVswCl
Vr = Vs – Is = Vs + Vsw 2 CLl 2
=Vs(1+ w 2 CLl 2 ).
7. The receiving end voltage at the no load will be ____________
a) Vs(1+ w 2 CLl 2 )
b) (1+ w 2 CLl 2 )
c) Vs/(1+ w 2 CLl 2 )
d) Vs
Answer: a
Explanation: The circuit diagram for the LTL is
power-systems-questions-answers-line-comensation-1-q7
Is= jVswCl
Vr = Vs – Is = Vs + Vsw 2 CLl 2
=Vs(1+ w 2 CLl 2 ).
8. If a line is considered with negligible power losses, then the real power transmitted will be proportional to sinδ.
a) True
b) False
Answer: a
Explanation: Pr = |Vs||Vr|/X.
9. If a line is considered with negligible power losses, then the real power transmitted will be proportional to ___________
a) sinδ
b) cosδ
c) δ
d) sin 2 δ
Answer: a
Explanation: Pr = |Vs||Vr|/X.
10. If a line is considered with negligible power losses, then the reactive power transmitted is proportional to receiving end voltage.
a) True
b) False
Answer: b
Explanation: Its incorrect, Q depends on the voltage drop across the line.
This set of Power Systems Questions and Answers for Entrance exams focuses on “Line Compensation – 2”.
1. If a line is considered with negligible power losses, then the real power transmitted will be proportional to voltage drop and the reactive power drop is proportional to cosδ.
a) True
b) False
Answer: b
Explanation: Real power = |Vs||Vr|/X
power-systems-questions-answers-entrance-exams-q1
2. If a line is considered with negligible power losses, then the real power transmitted will be proportional to ______ and the reactive power drop is proportional to ____
a) sinδ, voltage drop across line
b) cosδ, voltage drop across line
c) δ, voltage drop across line
d) voltage drop across line, sinδ
Answer: a
Explanation: Real power = |Vs||Vr|/X
power-systems-questions-answers-entrance-exams-q1
3. Choose the most feasible method for raising the power to be delivered at the reactive end.
Reducing the line reactance
Raising the voltage level
a)
b)
c) ,
d) None of the methods
Answer: a
Explanation: Increasing the voltage level is not always economical and reducing the voltages at stations is easier.
4. The lagging reactive power delivered by a line is proportional to the line _____ and independent of _____
a) voltage,δ
b) δ, voltage
c) voltage, sinδ
d) voltage drop, cos δ
Answer: a
Explanation: The lagging reactive power delivered by a line is proportional to the line voltage and independent of δ.
5. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
For obtaining 275 kV voltage at the receiving end obtaining unity power factor, the power transmitted will be _____________
a) 124 MW
b) 117.2 MW
c) 116 MW
d) 110 MW
Answer: a
Explanation: Qr = 0
0=/200 sin-0.8/200 sin
0=378sin-284.26
δ=26.23°
Pr = /200 cos-0.8/200 cos
= 124 MW.
6. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
For obtaining 275 kV voltage at the receiving end obtaining unity power factor, the power angle required to be set as __________
a) 26.23°
b) 22°
c) 25°
d) 24°
Answer: a
Explanation: Qr = 0
0=/200 sin-0.8/200 sin
0=378sin-284.26
δ=26.23°.
7. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
If a load is connected at receiving end at unity power factor but maintaining the same voltage profile. Will this system now need any type of compensation?
a) Yes
b) No
c) Cannot be said
d) Never
Answer: a
Explanation: Yes this system will require a compensation system to be employed as the net reactive power will not be zero due to the load mentioned.
8. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
If a load is connected at receiving end at unity power factor but maintaining the same voltage profile. Will this system now need any type of compensation? If so, then which one?
a) Yes, capacitive
b) No
c) Yes, inductive
d) Yes, inductive and capacitive
Answer: a
Explanation: yes, it will need compensation. As ∆Q≠0 and it will be less than zero.
9. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
If a load is connected at receiving end at unity power factor but maintaining the same voltage profile. Then _________ compensation will be needed at ______
a) capacitive, receiving end
b) inductive, sending end
c) capacitive, sending end
d) inductive, receiving end
Answer: a
Explanation: The positive VARs are to be fed to the line at the load end.
10. Assume a 275 kV transmission line having the following line constants:A = 0.85∠5° ; B = 200∠75°
If a load is connected at receiving end at unity power factor but maintaining the same voltage profile. The receiving end voltage if the compensation equipment is not installed will be __________
a) 245 kV
b) 280 kV
c) 255 kV
d) 272 kV
Answer: a
Explanation: Pr = 150 MW, Qr = 0
|Vs| = 275 kV, |Vr| = ?
150 = /200 cos-0.8/200 cos
0=/200 sin-0.8/200 sin
Solving the quadratic equations above and retaining the higher value for the voltage, |Vr| = 245 kV.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Comparison of Angle and Voltage Stability – 1”.
1. For the figure depicting the two generators connected via the transmission line having and impedance ‘jX’ ohms. Machine A at voltage Va at angle δ will supply active power to machine B at voltage Vb and angle zero, when δ is _____________
power-systems-questions-answers-comparison-voltage-stability-angle-1-q1
a) positive
b) negative
c) zero
d) any of the mentioned
Answer: a
Explanation: The real power transfer takes place when the power angle is greater than the other station.
2.For the figure depicting the two generators connected via the transmission line having and impedance ‘jX’ ohms. Machine A at voltage Va at angle δ will supply active power to machine B at voltage Vb and angle zero, when δ is _____________
power-systems-questions-answers-comparison-voltage-stability-angle-1-q2
a) Va>Vb
b) Va<Vb
c) Va = Vb
d) Any of the mentioned.
Answer: a
Explanation: The reactive power that will flow through the system when the voltage of the bus is more than the other one.
3. A three phase alternator can supply a maximum of 5000 KVA at 66 kV. The machine has internal resistance of 6%. The reactance per phase of the limiting reactor if the steady apparent power on the short circuit do not exceed 5 times full load is ____________
a) 1.22 Ω
b) 2.44 Ω
c) 5 Ω
d) 1.84 Ω
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-1-q3
4. A transmission line has Z= Ω has 10% of the voltage regulation with the lagging load of 0.8. If the load is 0.707 leading, the V.R. is ________
a) -6.63%
b) -5.77%
c) -10%
d) -8.63%
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-1-q4
5. A generating station has a connected load of 43 MW. The unit generated having 61.5*106 per year. The load factor will be _____________
a) 0.35
b) 0.33
c) 0.5
d) 0.45
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-1-q5
6. The symmetrical components are used in fault analysis because of _______________
a) sequence of network do not have mutual coupling
b) number of equations is smaller
c) results are required in symmetrical components
d) none of the mentioned
Answer: a
Explanation: Due the non-coupling of the transmission system sequence network it is easy to implement symmetrical fault analysis.
7. Two conductors of a single phase line, having the 1cm diameter and arranged in a vertical plane with one conductor mounted 1m above other. A second identical line is mounted at same height as first and spaced horizontally 0.25m apart. The two upper and lower conductors are connected in parallel. The loop inductance of the line is ______
a) 0.84
b) 0.42
c) 0.32
d) 0.64
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-1-q7
8. Two conductors of a single phase line, having the 1cm diameter and arranged in a vertical plane with one conductor mounted 1m above other. A second identical line is mounted at same height as first and spaced horizontally 0.25m apart. The two upper and lower conductors are connected in parallel. The inductance of the line is __________
a) 0.42
b) 0.84
c) 0.55
d) 0.80
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-1-q8
9. A transmission line has line parameters A =0.8, B= 200ʟ90o, C = 0.5*10 -6 operating at 400kV at no load. The sending current in line will be ___________
a) 0.1443
b) 1.443
c) 0.324
d) 3.245
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-1-q9
10. A 2-wire ring distributor is 300m long and fed at 240V at ‘A’. At ‘B’, 150m away from A, a load of 120A is taken and at ‘C’, 100m away in opposite direction a load of 80A is taken. If the resistance per 100m of single conductor is 0.03Ω, then current in section AB feeder is ___________
a) 86.67 A
b) 48.76 A
c) 88 A
d) 98.4 A
Answer: a
Explanation: Resistance per 100m of distributor = 2*0.03 = 0.06Ω
power-systems-questions-answers-comparison-voltage-stability-angle-1-q10
power-systems-questions-answers-comparison-voltage-stability-angle-1-q10-exp
This set of Power Systems Questions and Answers for Campus interviews focuses on “Comparison of Angle and Voltage Stability – 2”.
1. For a given system consisting of two generators
Units Rating Speed Drop
1. 400 0.04
2. 800 0.05
The units share load of P1=200MW and P2=600MW. The units are operating in parallel to share a load of 700 MW at 50 HZ. The load is increased by 130MW with B=0. Then the value new steady state frequency variation is ______________
a) 49.75 Hz
b) 51.25 Hz
c) 49.25 Hz
d) 48.75 Hz
Answer: a
power-systems-questions-answers-campus-interviews-q1
2. A 50 bus power system Ybus has 80% sparsity. The total number of transmission lines will be ___________
a) 225
b) 500
c) 475
d) 100
Answer: a
Explanation: Number of non zero elements = 50*50*20/100 = 500 non zero
Number of TL = /2 = 225 transmission lines.
3. The given graph is the depiction of ________ on a large power system network.
a) L-G fault
b) Three phase motor getting short
c) Fault in feeder
d) Any of the mentioned
Answer: a
Explanation: A LG fault will create a sudden dip in the voltage profile and it will be recovered.
4. A single core cable is graded by using three dielectrics with relative permittivity 5,4,3 respectively. The diameter of the conductor is 2cm and the overall diameter is 8 cm. If the three dielectric work at the same maximum stress of 40kV/cm, then the safe working rms voltage of cable is ______ kV
a) 57.72
b) 81.63
c) 84.67
d) 71.63
Answer: a
Explanation: d=2cm, d1 = ?, d2= ?, D = 8cm
Ԑ1 = 5; Ԑ2 = 4; Ԑ3 = 3
gmax =40 kV/cm
Ԑ1d1 = Ԑ2d2 = Ԑ3d3
d1 = 2.5cm, d2 = 3.33 cm
power-systems-questions-answers-comparison-voltage-stability-angle-2-q4
Rms value of the peak voltage = 81.63/√2 = 57.72 kV.
5. A generator delivers power of 1 pu to an infinite bus through a purely reactive network. The maximum power that could be delivered by generator is 2 pu. A three phase fault occurs at the generator which reduces the generator output to zero. The fault is restored after ‘tc’ seconds. The maximum swing of rotor angle is found to be δmax = 110o electrical. The rotor angle at ‘tc’ is ________ electrical deg.
a) 69.14 o
b) 159.14 o
c) 63.08 o
d) 65.7 o
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-2-q5
6. A system consists of an alternator having reactance of 0.5pu connectedto an infinite bus through a series of reactance of 1 pu. The generator terminal voltage of IBB is 1 pu and that of 1.2 pu. The steady state power system limit is ___________
a) 1.152
b) 1.167
c) 1.765
d) 1.729
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-2-q6
7. A system consists of an alternator having reactance of 0.5pu connected to an infinite bus through a series of reactance of 1 pu. The generator terminal voltage of IBB is 1 pu and that of 1.2 pu. The Steady state occurs at power angle of ________degree.
a) 0
b) 90
c) 180
d) 45
Answer: a
Explanation: It occurs at δ=90 o .
8. A system consists of an alternator having reactance of 0.5pu connectedto an infinite bus through a series of reactance of 1 pu. The generator terminal voltage of IBB is 1 pu and that of 1.2 pu.The emf induced in the alternator for the maximum power transfer will be __________
a) 1.729
b) 1.152
c) 1.2
d) 1.6
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-2-q8
9. A system consists of an alternator having reactance of 0.5pu connected to an infinite bus through a series of reactance of 1 pu. The generator terminal voltage of IBB is 1 pu and that of 1.2 pu. The emf induced in the alternator will have the phase difference with respect to reference for the maximum power transfer is _______________
a) 90
b) 0
c) 73.87
d) 86.25
Answer: a
Explanation: It occurs at δ=90 o for the maximum power transfer.
10. A three phase transmission line is having a three unit suspension insulation string. The voltage at the insulator unit nearest to the line is 20kV and that across the adjacent unit is 15 kV. The ratio of mutual to ground capacitance is ________________
a) 0.18
b) 0.2
c) 0.333
d) 0.16
Answer: a
power-systems-questions-answers-comparison-voltage-stability-angle-2-10
This set of Power Systems Multiple Choice Questions & Answers focuses on “Distribution Systems – 1”.
1. A transmission and distribution engineer needed to design the sub transmission substation. The tapping component needed will be _______________
a) feeder
b) distributor
c) transmitter
s) tap-changing transformer
Answer: a
Explanation: For the sub transmission level, there is no tapping at various level does not take place. For this a feeder is used.
2. While designing the distribution to locality of one lac population with medium dense load requirement, we can employ ___________
a) radial system
b) parallel system
c) ring main system
d) any of the mentioned
Answer: a
Explanation: A radial system is used for the medium requirement of loading and a medium dense population as it becomes easier to install and operate.
3. A _________ distribution system is more reliable than the ______ distribution system.
a) parallel, radial
b) parallel, ring
c) radial, parallel
d) ring, parallel
Answer: a
Explanation: A parallel distribution system has two end feeding and an alternative of parallel line, so in case there is a fault, the isolator can isolate the faulty part and let the healthy system operate.
4. For the figure shown, having a 2-wire dc system where mid point is earthed, having resistance of 20 ohms, with a power transmitted of 5 MW at the voltage level of 440 kV.
The power loss of the distribution system will be ___________
power-systems-questions-answers-distribution-system-1-q4
a) 5165 W
b) 515 kW
c) 10330 W
d) 2583 W
Answer: a
Explanation: I = P/V = 5000000/440000 = 11.36 A
Power loss = 2I2*R = 2* 11.362*20 = 5165 W.
5. For the figure shown, having a 2-wire dc system where mid point is unearthed, having resistance of 20 ohms, with a power transmitted of 5 MW at the voltage level of 440 kV.
The power loss of the distribution system will be ___________
power-systems-questions-answers-distribution-system-1-q5
a) 5165 W
b) 515 kW
c) 10330 W
d) 2583 W
Answer: d
Explanation: I = P/V = 5000000/440000 = 11.36 A
Power loss = I2*R = 2* 11.362*20 = 2583 W.
6. A DC 2-wire system with mid-point earthed having cross-sectional area of each conductor be ‘a’ and resistance ‘R1’. If the DC tow wire replaces the system, then the ratio of volume of each conductor V1/V2 will be ___________
a) ¼
b) ½
c) 4
d) 2
Answer: a
Explanation: Let the power losses remain constant over the systems, then
2P 2 R/V 2 = 2P 2 R1/2*V 2
or, R = R1/4;
As R = lρ/a;
a 1 = a/4;
So, V 1 /V 1 = 1/4.
7. While designing the distribution sub stations by the designer, it is required to use the _______ for the discrete power tapping.
a) distributor
b) power transformer
c) distribution transformer
d) feeder
Answer: a
Explanation: For the discrete tapping of the power the consumer level it is the distributor which is employed at the sub stations and consumer levels.
8. A DC 2-wire system with mid-point earthed having cross-sectional area of each conductor be ‘a’ and resistance ‘R1’. If this is replaced by monopolar system, then saving of copper will be ______
a) ½
b)b¼
c) 2
d) 4
Answer: a
Explanation: Let the power losses remain constant over the systems, then
2P 2 R/V 2 = 2P 2 R1/V 2
or, R1 = R
As R = lρ/a;
a 1 = a
So, V 1 /V 1 = a 1 *2l/a 1 = 1/2.
9. For the single phase 2-wire system, the maximum voltage between the outer wires and earth is ______________
a) V/√2
b) √2V
c) V
d) 2V
Answer: a
Explanation: The midpoint voltage will be V/√2.
10. For the given distribution system the maximum voltage at the midpoint will be ________
a) 155.6 V
b) 311.12 V
c) 622 V
d) 220 V
Answer: a
Explanation: Vmax = V/√2 = /√2 = 155.6 V.
This set of Power Systems Questions and Answers for Aptitude test focuses on “Distribution Systems – 2”.
1. For the given circuit diagram for the substation the voltage between the two outer conductors is
__________
power-systems-questions-answers-aptitude-test-q1
Answer: b
Explanation: The maximum voltage levels between the two outer conductors is double the supply fed to it and the its rms is √2 V.
2. For the given circuit diagram for the substation fed with 315 kV, the voltage between the two outer conductors is ____________
a) 445.5 kV
b) 890 kV
c) 630 kV
d) 223 kV
Answer: a
Explanation: The maximum voltage levels between the two outer conductors are double the supply fed to it and its rms is √2V.
Voltage between the two outer conductors is √2*315 kV = 445.5 kV.
3. If a 2-wire ac single phase distribution system operating at ‘P’ MW and ‘V’ kV, operating at the power factor of 0.8, then the current in the outer wire in kA is ______
a) 0.8P/V
b) 1.131P/V
c) 1.88P/V
d) 0.088P/V
Answer: a
Explanation: I = P/Ø = 0.88P/V.
4. If a 2-wire ac single phase distribution system operating at ‘30’ MW and ‘315’ kV, operating at the power factor of 0.8, then the current in the outer wire in kA is _____
a) 0.0838
b) 83.8
c) 8.38
d) 1.131
Answer: a
power-systems-questions-answers-distribution-system-2-q4
5. For a 2-wire ac single phase distribution system operating at ‘30’ MW and ‘315’ kV, operating at the power factor of 0.8 having 15Ω of resistance of each wire, then the copper loss at the substation in kW will be ___________
a) 210.67
b) 105.33
c) 240.87
d) 108.27
Answer: a
Explanation: Current in the line, power-systems-questions-answers-distribution-system-2-q5
Power losses = 2*I 2 *R = 2*83.822*15 = 210.673 kW.
6. For a 2-wire ac single phase distribution system operating at ‘30’ MW and ‘315’ kV, operating at the power factor of 0.8 having 15Ω of resistance of each wire, then the power received at the consumer end will be ____________
a) 29.79 MW
b) 29.895 MW
c) 29.76 MW
d) 29 MW
Answer: a
Explanation: Current in the line, power-systems-questions-answers-distribution-system-2-q5
Power losses = 2*I 2 *R = 2*83.822*15 = 210.673 kW
Power received = 30-210.67 = 29.79 MW.
7. For a 2-wire ac single phase distribution system operating at ‘P’ MW and ‘V’ kV, operating at the power factor of 0.8. The copper losses of the system will be proportional to ___________
power-systems-questions-answers-distribution-system-2-q7
Answer: a
power-systems-questions-answers-distribution-system-2-q7-exp
8. The maximum rms voltage between one phase and ground neutral for a three phase 4-wire ac system will be ____________
a) 221.32 kV
b) 313 kV
c) 442 kV
d) 127 kV
Answer: a
Explanation: The maximum rms phase voltage = Vph/√2 = 313/√2 = 221.32 kV.
9. The maximum rms voltage between one phase and ground neutral for a three phase 4-wire ac system will be ___________________
a) 171.46 kV
b) 242.5 kV
c) 221 kV
d) 127 kV
Answer: a
Explanation: The maximum rms phase voltage = Vph/√2 = 420/√ = 221.32 kV.
10. For the circuit diagram as depicted in the figure, the current per phase under balanced condition with a consumer end load of 90 kW, 414V operating at a power factor of 0.65 is ___________
a) 157.66 A
b) 152 A
c) 111.4 A
d) 193.1 A
Answer: a
Explanation: Current per phase in the line, I = P/Ø = 90000/ = 157.66 A.
This set of Power Systems Assessment Questions and Answers focuses on “Distribution Systems – 3”.
1. For an ac three-phase four wire system, having a voltage of 415V, with load of 120 kW and resistance of 0.05Ω at power factor of 0.75. The incurred copper losses of the system is ____
a) 4.955 kW
b) 47 kW
c) 49 kW
d) 7.9 kW
Answer: a
Explanation: Copper losses for a three-phase four wire system will be,
power-systems-assessment-questions-answers-q1
2. The ratio of area of cross section of the wire of a 3-phase 3-wire and that of dc 2-wire mid point earthed system will be _________
power-systems-questions-answers-distribution-system-3-q2
Answer: a
Explanation: The ratio of area of cross section of the conductor used in 3-ph 3-wire to dc 2-wire will be power-systems-questions-answers-distribution-system-3-q3-exp as the power factor will come into picture.
3. Distributors fed at both ends has an advantage of ________________
a) continuous supply
b) fault isolation
c) being economical
d) all of the mentioned
Answer: d
Explanation: All the points mentioned are the benefits of the dual fed distribution system.
4. Why is a ring main distribution system preferred to a radial system?
1. Voltage drop in feed is more
2. Supply is reliable
3. Power factor is higher
a) 2
b) 1,2
c) 1,2,3
d) 2,3
Answer: a
Explanation: Ring main system has less voltage drop and power factor at the consumer level is not high.
5. For a given power delivered, if the working voltage of a distribution line is decreased to ‘x’ times, the cross sectional area ‘a’ of distributor line would reduce to ___________
power-systems-questions-answers-distribution-system-3-q5
Answer: d
Explanation: The cross-sectional area has to be increased not reduced after reducing the voltage levels.
6. For a given power delivered, if the working voltage of a distribution line is increased to ‘x’ times, the cross sectional area ‘a’ of distributor line would reduce to _____________
power-systems-questions-answers-distribution-system-3-q5
Answer: a
Explanation: Assuming the power at both the times remain constant.
power-systems-questions-answers-distribution-system-3-q6
7. The distribution feeding system of ring main system has ______________
a) one feeder
b) 2 feeders
c) 4 feeders
d) cannot be said
Answer: a
Explanation: Ring main uses only one feeder.
8. A substation records a dip in the voltage received by 15%. To overcome this issue, the booster employed at the substation is ___________
a) a series wound generator coupled to dc shunt motor
b) a series wound motor
c) a shunt motor operating at lagging power factor
d) a shunt motor coupled to differential motor
Answer: a
Explanation: A dc series motor coupled with the shunt motor has the ability to boost the voltage at its input supply.
9. A substation records a dip in the voltage received by 15%. To overcome this issue, the booster employed at the substation which should have a _____________
a) low voltage and high current generator
b) high voltage and low current generator
c) medium voltage but high current generator
d) any of the mentioned
Answer: a
Explanation: The booster need to have the low voltage and high current profile so that it can easily boost the voltage levels at its output.
10. Single core cables for an ac systems are not provided with armouring.
a) True
b) False
Answer: a
Explanation: Because of the armouring of the cables leads to eddy current in the power cables adding more to the losses.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Underground Cables – 1”.
1. Single core cables for AC systems are not provided with armouring.
a) True
b) False
Answer: a
Explanation: Because of the armouring of the cables leads to eddy current in the power cables adding more to the losses.
2. Single core cables for ac systems are provided with armouring.
a) True
b) False
Answer: a
Explanation: This is so because the eddy currents induced in the steel armour cause the additional power losses.
3. Potential gradient of single core cable is ________________
power-systems-questions-answers-underground-cables-1-q3
Answer: a
Explanation: The electric field intensity,
power-systems-questions-answers-underground-cables-1-q3-exp
4. For a transmission system of voltage ‘V’ volts having the core radius of ‘r’ m and outer radius of ‘R’ m. The maximum dielectric stress on single core cable is ___________
power-systems-questions-answers-underground-cables-1-q4
Answer: a
Explanation: The maximum stress will occur at the surface of the conductor such that x = radius of core.
5. For a transmission system of voltage ‘V’ volts having the core radius of ‘r’ m and outer radius of ‘R’ m. The minimum dielectric stress on single core cable is ______________
power-systems-questions-answers-underground-cables-1-q5
Answer: b
Explanation: The minimum stress will occur at the outermost surface of the conductor such that x = outer radius of core.
6. For a transmission system of voltage ‘765 kV’ volts having the core radius of ‘5’ cm and outer radius of ‘0.40’ m. The maximum dielectric stress on single core cable is _________
a) 7357.7 kV
b) 919.7 kV
c) 4247 kV
d) 530 kV
Answer: a
Explanation: The maximum stress will occur at the surface of the conductor such that x = radius of core.
power-systems-questions-answers-underground-cables-1-q6
7. The ratio of dielectric stress of the on the cable corresponding to the maximum and minimum is ____________
a) R/r
b) r/R
c) rR
d) 2
Answer: a
power-systems-questions-answers-underground-cables-1-q7
8. The condition at which the minimized dielectric stress condition will take place is ______________
a) 2.7188
b) 0.7188
c) 1/2.7188
d) 2.7188 2
Answer: a
power-systems-questions-answers-underground-cables-1-q8
9. Grading of the cables is performed in order to achieve ____________
uniform stress
reduction in quantity of insulation
reduction in quality of insulation
a) ,
b)
c) ,
d) ,
Answer: a
Explanation: Grading is performed to reduce the stress at one cable and to make it uniform throughout. Also it reduces the insulation material to be used and thus the cost saving.
10. The resistance of the insulation used for the cables is 40 ohms for a length of ‘x’ km. If the proposed plan needs to extend the transmission line cable to extra ‘2x’ m then the resistance of the cable offered will be _____________ .
a) 13.33
b) 20
c) 120
d) 40
Answer: a
Explanation: The resistance of the cable is inversely proportional to the length of it.
11. Consider a system having a cable of capacitance 5 nF, with 765 kV star connected at 50 Hz having a power loss in the cable as 82.1 kW. Then the dielectric loss angle is _________.
a) 15
b) 7.5
c) 20
d) 4.9
Answer: a
Explanation: Dielectric loss = ωCV 2 tanδ
power-systems-questions-answers-underground-cables-1-q11
12. Dielectric power loss of a transmission line cable operating for ‘V’ volts, ‘f’ Hz having a capacitance of ‘C’ Farads with the tangent loss angle of δis ____________
a) ωCV 2 tanδ
b) ωCV 2 /tanδ
c) 2
d) ωCV 2 tanδ 2
Answer: a
Explanation: The Dielectric loss = ωCV 2 tanδ for a cable.
13. The power losses occurring in the transmission cable has the relation with loss tangent angle as _____
a) power-systems-questions-answers-underground-cables-1-q13-a
b) power-systems-questions-answers-underground-cables-1-q13-b
c) power-systems-questions-answers-underground-cables-1-q13-c
d) power-systems-questions-answers-underground-cables-1-q13-d
Answer: a
Explanation: The Dielectric loss = ωCV 2 tanδ
So, Pd α tanδ.
14. In a transmission tower having ‘n’ insulators with equivalent pin-to-earth capacitance of ‘C’ farads. For the static shielding of the conductors, the capacitance from the shield to the kth link from the top is ______
power-systems-questions-answers-underground-cables-1-q14
Answer: a
Explanation: The generalized expression for the capacitance of the kth metal ring is,
C = k*pin-to-earth/.
This set of Power Systems Problems focuses on “Underground Cables – 2”.
1. For a string of five suspension insulators is to be fitted with a grading ring. If the pin to earth capacitances is equal to C, then the value of line to pin capacitance of first capacitance is
a) 0.25C
b) 0.667C
c) 1.5C
d) 4C
Answer: a
Explanation: Ck= KC/ = 1*C/5-1 = C/4.
2. For a string of five suspension insulators is to be fitted with a grading ring. If the pin to earth capacitances are equal to C, then the value of line to pin capacitance of first and last capacitance is
a) 0.25C, 4C
b) 0.667C, 3C
c) 1.5C, 1.5C
d) 4C,0.25
Answer: a
Explanation: Ck= KC/
C1= 1*C/ = C/4
C4 = 4C/ = 4C.
3. How does grading neutralize the potential distribution across the units of the suspension insulators?
a) By forming capacitances to cancel the charging current from link pins
b) By forming capacitances with link pin to cancel the charging current from them
c) By increasing the capacitance of lower insulator units
d) By decreasing the capacitance of lower insulator units
Answer: a
Explanation: The non uniform distribution of the voltage occurs due to the leakage currents at the pins. So grading is done to provide a capacitance which can neutralize these charging currents.
4. The capacitance grading method is one of the most practical and most widely used method in Indian transmission system.
a) True
b) False
Answer: b
Explanation: The capacitance grading method is uneconomical because it requires a large number of the different sized insulators.
5. A string of insulators consisting of 7 units. The voltage across the bottom most unit is 25% of the total voltage. The string efficiency of this system will be
a) 57.14 %
b) 50.6 %
c) 80.4 %
d) 67.7 %
Answer: a
Explanation: power-systems-problems-q5
6. For a line-man while measuring the string efficiency of the insulator installation done, observes that it shows a reading of 100%. This means ___________________
a) equal potential across each insulator disc
b) one of the insulator disc is shorted
c) zero potential across each disc
d) none of the mentioned
Answer: a
Explanation: As the equipotential exists between the plates there will not be any charging current and so 100% of efficiency.
7. The pin type insulators are generally not used for the voltage range exceeding ____________
a) 33kV
b) 66kV
c) 25kV
d) 11kV
Answer: a
Explanation: The pin type insulators have the ceramic material and the string structure of it can not sustain the voltage above 33kV.
8. If the frequency of the transmission line is changed from 50 Hz to 100 Hz, then the string efficiency ____________
a) remains unchanged
b) increases
c) decreases
d) May or may not increase depending on the parameters
Answer: a
Explanation: The string efficiency is independent of system frequency.
9. For a 400 kV, 50 Hz five pin insulator setup provides the protection with an efficiency of 87.4%. The same setup is now meant to be used at the frequency of 60 Hz, the updated string efficiency of the system will be ____________
a) 87.4
b) 91
c) 82%
d) 86%
Answer: a
Explanation: The string efficiency is independent of system frequency.
10. How can one think of reducing the earth capacitance of line?
a) Using guard ring
b) Using special designed earth capacitances
c) Implementing parallel insulator lines
d) Any of the mentioned
Answer: a
Explanation: The guard rings can provide an economical protection to the string and it is very simple method.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Insulator for Overhead Lines – 1”.
1. Which of the following material is not used for overhead line insulators?
a) Porcelain
b) Glass
c) PVC
d) Steatite
Answer: c
Explanation: In addition to high insulation resistance and high relative permittivity, overhead line insulators must have high mechanical strength to bear the weight of line insulators, wind stress and ice loading if any. PVC have good insulation resistance but it does not have such mechanical strength so it is not suitable for overhead line insulators.
2. Pin type insulator are mostly subjected to which type of mechanical stress?
a) Compressive stress
b) Tensile stress
c) Both tensile and compressive stress
d) Twisting stress
Answer: d
Explanation: The conductor is placed in the governor at the top of the insulator and is tied down. So the weight of wire acts on the top of the insulator in downward direction causing compressive stress on insulator. No tensile stress is acted on the pin type insulator.
3. Which of the following is the main field of application of pin type insulator?
a) Distribution system
b) Transmission system
c) Transmission and distribution system
d) EHV transmission system
Answer: a
Explanation: Pin type insulator become very bulky and cumbersome when designed for higher voltage. Pin insulators beyond 50,000 Volts becomes uneconomical. the modern practice is not to use pin type insulator SBI on 33kv so use of pin insulator is limited to distribution level voltage.
4. Suspension type insulator are subjected to ______________
a) tensile stress
b) compressive stress
c) tensile and compressive stress
d) depends on its use
Answer: a
Explanation: Suspension type insulator hangs from the cross arms of the suspending supporting structure. The line conductor is attached to its lower end hence the load of the conductor causes tensile stress on the suspension insulator.
5. A transmission line consists of 9 discs of suspension insulator in each string. What is the operating voltage of the transmission line?
a) 11 KV
b) 33 KV
c) 66 KV
d) 132 KV
Answer: d
Explanation: For different voltage it does not need to use different suspension insulator. Srength of insulator can easily be increased just by adding extra disc of suspension insulators. For 130 KV transmission lines 9 or 10 disks are used.
6. Suspension insulator are made up of _____________
a) glass
b) porcelain
c) steatite
d) epoxy resin
Answer: b
Explanation: Suspension insulators consist of a number of porcelain disks flexibly connected in series by metal links in the form of Strings. Glass is used for making pin type insulators.
7. Which of the following insulator is similar to pin type insulator?
a) Suspension insulator
b) Post insulator
c) Strain insulator
d) Shackle insulator
Answer: b
Explanation: Post insulators are very similar to pin type insulator, but has a metal base with a metal cap so that more than one unit can be mounted in series. Suspensions train and shackle insulators are completely different from pin type insulator on the basis of construction.
8. Which type of insulator is used where there is dead end of the line or there is a corner or a sharp curve, for high voltage line?
a) Pin type insulator
b) Shackle insulator
c) Strain insulator
d) Stay insulator
Answer: c
Explanation: Pin type insulators cannot be used in such situations because they cannot take conductor mechanical load intention which often occurs in such situations for low voltage line. Shackle insulator can be used but for higher voltages transmission lines strain insulator consisting of assembly of suspension type insulator are used.
9. What is the most common cause of failure of overhead line insulators?
a) Flashover
b) Mechanical stress
c) Porosity of materials
d) Improper vitrification
Answer: a
Explanation: Failure of overhead line insulators due to mechanical stress is rare because defective pieces are separated during routine factory test. Failure due to porosity and improper vitrification is also very low. The most common cause of failure of overhead line insulator is flashover.
10. If a string of suspension insulator has three units, each can withstand a maximum 11 KV and total string can withstand 25.76 KV. What is the string efficiency?
a) 234.1%
b) 46.3%
c) 68.75%
d) 78%
Answer: d
Explanation: String Efficiency = [ /] × 100
Where ‘n’ is number of units in one string
Hence, String Efficiency = [25.76/] × 100
= 78%.
11. Voltage distribution across disc of strings of suspension insulator assembly is ______
a) same for all disks
b) maximum for unit nearest to the line
c) maximum for unit nearest to the tower
d) equal to transmission line voltage rating
Answer: b
Explanation: Thee voltage between line conductor and Earth is not distributed uniformly across individual disks. The unit nearest the conductor has the maximum value across it. The figure progressively decreases as the unit nearest the cross on is approach.
This set of Basic Power Systems Questions and Answers focuses on “Insulator for Overhead Lines – 2”.
1. The unequal voltage distribution across individual unit of string of suspension insulator is __________
a) desirable and expressed by string efficiency
b) undesirable and expressed by string efficiency
c) desirable and expressed by impulse ratio
d) undesirable and expressed by impulse ratio
Answer: b
Explanation: The unequal potential distribution is undesirable and is expressed in terms of string efficiency. Impulse ratio is calculated during Impulse Frequency Flash Over Test. Impulse ratio is the ratio of impulse park over voltage to Spark over voltage at power frequency.
2. Glass insulator cannot be used for voltage above __________
a) 25 KV
b) 11 KV
c) 33 KV
d) 50 KV
Answer: d
Explanation: Glass is cheaper than porcelain in the simplest shapes and if properly toughened and annealed gives high resistivity and dielectric strength. The main disadvantage of Glass is that moisture more readily condenses on its surface and facilitates the accumulation of dust deposit thus giving a high surface leakage. Hence, glass insulators can be used upto 25 KV under ordinary atmosphere and well upto 50 KV in dry atmosphere.
3. Which of the following location is suitable to use shackle insulator?
a) Sharp Turn in transmission line
b) Dead end of low voltage distribution line
c) For bearing High Voltage transmission line conductor
d) Dead end of EHV transmission line
Answer: b
Explanation: Shackle insulator are almost universally used for low voltage lines. They can be used at all positions either intermediate terminal or angle where the angle exceed 60 degree deviation. They are generally used in conjunction with shackle sharps.
4. Which of the following insulator is used for insulating stay wire from pole?
a) Pin type insulator
b) Shackle insulator
c) Suspension insulator
d) Stay insulator
Answer: d
Explanation: Stay insulators are also called as guy insulators and are used in guy cables. Because it is necessary to insulate the lower part of the guy cable from pole for safety of people and animals on the ground.
5. What is the reason for unequal distribution of voltage among different unit of suspension insulator?
a) Unequal capacitance of different units
b) Unequal distribution of charging current caused by stray capacitance
c) Unequal resistivity of different units
d) Dirt deposited over the insulator disc
Answer: b
Explanation: The capacitance due to two metal fittings on either side of insulator is known as the mutual capacitance and the capacitance between these metal fittings and earthed pole or tower is known as shunt capacitance. Due to shunt capacitance charging current is not the same through all the discs of strings. So voltage being directly proportional to the current flowing through them will be different.
6. Arcing horns are used for ______________
a) protecting insulators from birds
b) protecting insulators from cracking or breaking due to flash over
c) improving string efficiency
d) protecting insulator from deposition of dirt
Answer: b
Explanation: During flash over insulators are cracked or broken up due to the heat of Arc. Grading ring in addition to equalization of voltage distribution across the insulators unit when used in conjunction with Arcing horns protects the insulator string from flashover. It does so by keeping the arc away from the insulator string until it is interrupted by protecting devices.
7. What is the effect of rain on string efficiency?
a) It becomes very low
b) It reduces slightly
c) It does not changes
d) It is improved
Answer: d
Explanation: Due to rain insulators becomes wet and mutual capacitance increases while the shunt capacitance remains constant thereby decreasing the value of k. As k is inversely related to string efficiency so, string efficiency is improved. K is the ratio of stray capacitance to mutual capacitance.
8. A suspension string have 3 units. Voltage across topmost and lower most unit of string are 6.71 volts and 11 volts respectively. What is the voltage across middle string, if voltage across whole string is 25.76 volts?
a) 103.47 volts
b) 8.05 volts
c) 83.6 volts
d) 25.76 volts
Answer: b
Explanation: Voltage across whole string is equal to the sum of voltage across each unit. From this the voltage across middle unit can be calculated.
9. If voltage across lowermost unit of a string is 34.8% of voltage across whole string and string efficiency is 57.46%. What is the voltage across whole string.
a) 100%of line voltage
b) 43.64% of line voltage
c) 75.2% of line voltage
d) 92.26% of line voltage
Answer: a
Explanation: Voltage across string is equal to the line voltage of conductor. So it is 100% of line voltage.
10. By using which of the following method hundred percent string efficiency can be achieved?
a) Using long cross arms
b) Capacitance grading
c) Static shielding
d) 100% string efficiency cannot be achieved
Answer: d
Explanation: 100% string efficiency can only be achieved by making voltage distribution across each unit of string equal. In practice it is impossible to attain such uniform voltage distribution. So 100% string efficiency cannot be achieved with any of the above methods.
This set of Power Systems Multiple Choice Questions & Answers focuses on “Switchgear and Protection – 1”.
1. The factor which influences the acr de ionisation dominantly ________
a) line voltage
b) magnitude of transient fault current
c) speed of reclosure
d) all of the mentioned
Answer: a
Explanation: The line voltage determines the arc de ionisation in a circuit breaker.
2. A three phase transformer having a line voltage ratio of 400/33000 V is connected in the star-delta. The CTs on the 400V side have a CT ratio of 1000/5. What must be the ratio of CTs on the 33000 side?
a) 7/5
b) 5/7
c) 3/5
d) 5/2
Answer: a
Explanation: As the power levels remain same at the two sides of transformer,
√3*400*1000 = √3*33000*IL2
IL2= 400/33
Current through the secondary of CT on the primary side = 5A
Current through the pilot wire = 5√3 A
So CTs on the secondary side being star connected will have 5√3 A.
CT ratio on 33000V side = 400/ = 7/5.
3. A three phase transformer having a line voltage ratio of 400/33000 V is connected in the star-delta. The CTs on the 400V side have a CT ratio of 1000/5. What will be the current through the pilot wire?
a) 5√3 A
b) 5/√3 A
c) 5 A
d) 1/5 A
Answer: a
Explanation: As the power levels remain same at the two sides of transformer,
√3*400*1000 = √3*33000*IL2
IL2= 400/33
Current through the secondary of CT on the primary side = 5A
Current through the pilot wire = 5√3 A.
4. The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What percentage of the winding is protected against L-G faults?
a) 76.4
b) 77.8
c) 73
d) None of the mentioned
Answer: d
Explanation: The given system will not protect for the LG faults, instead it will protect for earth faults.
5. The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What percentage of the winding is protected against earth faults?
a) 76.4
b) 77.8
c) 73
d) None of the mentioned
Answer: a
Explanation: The primary CT current for the relay operation = 1.5*1000/5 = 300 A
power-systems-questions-answers-switchgear-protection-1-q5
6. The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What percentage of the winding is protected against L-G faults?
a) 76.4
b) 23.6
c) 73
d) None of the mentioned
Answer: b
Explanation: The primary CT current for the relay operation = 1.5*1000/5 = 300 A
% winding unprotected =
= /11000*100
= 23.6 %.
7. The neutral of the three phase 20 MVA, 11kV alternator is earthed through a resistance of 5 ohms, the relay is set to operate when there is an out of balance current of 1.5 A. The CTs have a ratio of 100/5. What should be the minimum value of the earthing resistance to protect 90% of winding?
a) 2.12 Ω
b) 1.12 Ω
c) 4.24 Ω
d) 3.24 Ω
Answer: a
Explanation: % winding protected = 76.4 %
resistance required to protect 90% of the winding
10 = Is*RV*100
R = 2.12 Ω.
8. While a transformer is energised, the differentially connected relay will
a) mal operate
b) not mal operate
c) mal operate for lagging loads
d) never mal operate
Answer: a
Explanation: There will be flow of inrush current at the energization of transformer which will let relay may operate.
9. If a transformer is provided with differentially connected relay. To prevent the mal operation of the relay, the relay relay operating coil is biased with ______
a) 3rd harmonic
b) 2nd harmonic
c) 7th harmonic
d) 5th harmonic
Answer: d
Explanation: The restraining coil will be biased not the operating coil. The transformer having heavy inrush current has 2nd harmonic components.
10. If a transformer is provided with differentially connected relay. To prevent the mal operation of the relay, the relay restraining coil is biased with ______________
a) 3rd harmonic
b) 2nd harmonic
c) 7th harmonic
d) 5th harmonic
Answer: b
Explanation: The transformer having heavy inrush current has 2nd harmonic components.
11. The frequency of the carrier in the case of carrier-current-pilot scheme is in the range of _________
a) 50 kHz-500 kHz
b) 1 kHz-10 kHz
c) 25 kHz-50 kHz
d) 15 kHz-25kHz
Answer: a
Explanation: The carrier frequency has to be high in the case of carrier-current-pilot scheme.
This set of Advanced Power Systems Questions and Answers focuses on “Switchgear and Protection – 2”.
1. A protection system engineer is planning to provide the complete protection, he can achieve this by ___________
a) three phase fault relays and two earth fault relays
b) two phase fault relays and three earth fault relays
c) a two phase fault relays and three earth fault relays
d) a two phase fault relays and two earth fault relays
Answer: a
Explanation: For the complete protection of the power system, one can use 3 phase fault relays and two earth fault relays so that to cover the entire zone of operation.
2. The given figure shows protection system scheme for one phase of generator. A high resistance fault occurs near the neutral end with the current distribution as marked. The slope of the relay is 10% and pick-up current of 0.15A.
The CT ratio is 500/5.
Will the relay operate under given circumstances?
a) True
b) False
Answer: b
Explanation: I oc = i 1 -i 2
I RS = (i 1 +i 2 )/2
Relay will operate only if i R > k(i 1 +i 2 )/2+i0
I 1 = 435/
I 2 = 400/
I r = i 1 -i 2 = 4.35-4.0 = 0.35 A
i 1 +i 2 = 4.175 A
k(i 1 +i 2 )/2+i 0 = 0.1*4.175 + 0.15 = 0.5675 > 0.35
Therefore, the relay will operate.
3. We need the biasing of differential relay biased to avoid mal operation when used for transformer protection due to ____________
a) mismatch of CT
b) saturation of
c) difference in connection of both sides of CT
d) current setting mismatch
Answer: a
Explanation: It is not practical to use CT of exact type, so the mal operation may occur due to mismatch of current transformers.
4.If the specified fault setting for a winding is mentioned as 20%, then what can be inferred about it?
a) If a terminal fault has its current limited to the full load rating, then 20% of winding from neutral end will be unprotected
b) If a terminal fault has its current limited to the full load rating, then 80% of winding from neutral end will carry current
c) If a terminal fault has its voltage limited to the full load rating, then 20% of winding from neutral end will be unprotected
d) Any of the mentioned
Answer: a
Explanation: The fault setting implies that 20% of the neutral is unprotected.
5. The typical characteristic of the relay during loss of excitation is ____________
a) advanced-power-systems-questions-answers-q5
b) power-systems-questions-answers-switchgear-protection-2-q5-a
c) power-systems-questions-answers-switchgear-protection-2-q5-c
d) power-systems-questions-answers-switchgear-protection-2-q5-d
Answer: a
Explanation: The loss of excitation leads to a characteristic of the negative resistance offered.
6. The standard system fault characteristic of the relay is _____________
a) power-systems-questions-answers-switchgear-protection-2-q6-a
b) power-systems-questions-answers-switchgear-protection-2-q6-b
c) power-systems-questions-answers-switchgear-protection-2-q6-c
d) power-systems-questions-answers-switchgear-protection-2-q6-d
Answer: a
Explanation: The typical fault characteristic shown by a relay is the linear impedance offered by the fault currents.
7. A longitudinal differential protection on stator can detect inter-turn on the stator.
a) True
b) False
Answer: b
Explanation: Because inter-turn faults on the same phase of stator wdg does not disturb the balance between currents in neutral and high voltage CTs. Hence a transverse differential protection is used.
8. Bias is used in the relay protection to _______________
a) provide balanced sharing of current
b) reduce current level
c) deivert the current
d) none of the mentioned
Answer: a
Explanation: Bias is predominantly used for providing the balance in the current distribution.
9. Unbalancing of an alternator may occur due to ____________
a) single phase fault
b) unbalanced loading
c) line breaking
d) all of the mentioned
Answer: d
Explanation: All the mentioned reasons can cause unbalancing.
10. For the given earth fault for solidly earthed CT, the fault current as a percentage of the full load current is given as _______________
power-systems-questions-answers-switchgear-protection-2-q10
a) power-systems-questions-answers-switchgear-protection-2-q10-a
b) power-systems-questions-answers-switchgear-protection-2-q10-b
c) power-systems-questions-answers-switchgear-protection-2-q10-c
d) power-systems-questions-answers-switchgear-protection-2-q10-d
Answer: a
Explanation: The line current in the delta side will rise from zero and star connection will have maximum current.
This set of Tricky Power Systems Questions and Answers focuses on “Switchgear and Protection – 3”.
1. A power system network is connected as shown in the figure below.
tricky-power-systems-questions-answers-q1
Sd1=15+j5 pu
Sd2=25+j15 pu
Zcable = j0.05pu
|V1|=|V2|=1 pu. The torque angle for the system will be _______
a) 14.4
b) 22.1
c) 16.2
d) 18.2
Answer: a
Explanation: As the resistance is zero, losses will be zero.
P G1 =PD1+PD2=40 pu
For the equal sharing of load at the station
P G1 =P G2 =20pu
Real power flow from bus 1 to 2
power-systems-questions-answers-switchgear-protection-3-q1-exp
δ = 14.4 o .
2. A single phase distributor of 1 km long has resistance and reactance per conductor of 0.1Ω and 0.15 Ω respectively. If the far end voltage Vb=200V and current is at 100A at 0.8 lag. At the midpoint a current of 100A is tapped at a pf of 0.6 pf with ref to voltage Vm at mid point. The voltage magnitude at M is __________
a) 218V
b) 200V
c) 232V
d) 220V
Answer: a
Explanation: Drop in MB= ʟ= 18.027ʟ19.44
V M = 200+18.027 = 218.027 V.
3. A single phase motor is connected to 400V, 50Hz supply. The motor draws a current of 31.7A at a power factor 0.7 lag. The capacitance required in parallel with motor to raise the power factor of 0.9 lag is ___________
a) 94.62
b) 282.81
c) 108.24
d) 46.87
Answer: a
Explanation: Active power drawn by the motor=VIcosФ = 400*31.7*0.7 = 8876 W
Reactive power = VIsinФ=400*31.7*sin = 9055.3 VAR
New power factor=cosθ2 = 0.9
θ2=cos -1
Q2=8876*tan = 4298.855 VAR
Change in reactive power=9055.3-4298.855 = 4756.4 VAR
Qc = V 2 /Xc = V 2 *2πfC
C=4756.4/(400 2 *2π*50) = 94.62μF.
4. A single phase motor is connected to 400V, 50Hz supply. The motor draws a current of 31.7A at a power factor 0.7 lag. The additional reactive power to be supplied by the capacitor bank will be ___________
a) 4756
b) 4873
c) 4299
d) 9055.3
Answer: a
Explanation: Active power drawn by the motor=VIcosФ = 400*31.7*0.7 = 8876 W
Reactive power = VIsinФ=400*31.7*sin = 9055.3 VAR
New power factor=cosθ2 = 0.9
θ2=cos -1
Q2=8876*tan = 4298.855 VAR
Change in reactive power=9055.3-4298.855 = 4756.4 VAR.
5. A 275 kV TL has following line constants A=0.85ʟ5o, B=200ʟ75o. The active power received if the voltage to be maintained is 275kV will be ______________
a) 117.63
b) 220
c) 120
d) 115.25
Answer: a
Explanation: |Vs|=|Vr|=275 kV
α= 5 o , β= 75 o
power-systems-questions-answers-switchgear-protection-3-q5
6. A 275 kV TL has following line constants A=0.85ʟ5o, B=200ʟ75o. The active power angle such that the voltage to be maintained at the other end will be 275 kV ______________
a) 22
b) 16
c) 18
d) 24
Answer: a
Explanation: |Vs|=|Vr|=275 kV
α= 5 o , β= 75 o
power-systems-questions-answers-switchgear-protection-3-q6
7. A power system has a maximum load of 15 MW. Annual load factor is 50%. The reserve capacity of plant is _____ if the plant capacity factor is 40%.
a) 3.75 MW
b) 4.75 MW
c) 18.75 MW
d) 5.75 MW
Answer: a
power-systems-questions-answers-switchgear-protection-3-q7
Plant capacity= *15 = 18.75 MW
Reserve Capacity = 18.75-15 = 3.75 MW.
8. A 100 MVA synchronous generator operates on full load at a frequency of 50 Hz. The load is suddenly reduced to 50 MW. Due to time lag in governor system, the steam valve begins to close after 0.4s. The change in the frequency is ___________
a) 1
b) 0.5
c) -1.5
d) 0.8
Answer: a
Explanation: Energy transferred in 0.4 sec = 50*0.4= 20 J
power-systems-questions-answers-switchgear-protection-3-q8
9. A 50 Hz four pole turbo-generator rated 100 MVA, 11 kV has an inertia constant of 8 MJ/MVA. If the mechanical input is suddenly raised to 80 MW for an electrical load of 50MW, then the rotor acceleration is __________
a) 337.5
b) 3.375
c) 457.5
d) 4.57
Answer: a
Explanation: Energy stored = 100*8 =800MJ
Accelerating power = Md 2 δ/dt 2
M=GH/180f = 800/ = 4/45 MJs/elect. Deg
power-systems-questions-answers-switchgear-protection-3-q9
α= 337.5 elect deg/s 2 .
10. A single phase TL has copper conductor of 0.775 cm2 cross section through which 200 kW at UPF at 330 V is to be maintained. If the efficiency of transmission line is 90%, then the minimum length of TL is _________.
a) 13.6 km
b) 14 km
c) 136 km
d) 16.4 km
Answer: a
Explanation: Pr=200 kW, efficiency=0.9
Ps= 200/0.9=222.22 kW
Losses=22.22 kW
Current, I=200000/3300 = 60.60 A
Line losses=2I 2 R
R=22.22/=3.02 Ω
R=ρl/a
Length, l = / = 13.6 km.
11. An isolated generator connected to a turbine with its continuous maximum power of 20 MW, 50 Hz. Generator connected with two loads of 8 MW, each operate at 50 Hz.. Generator has 5% droop characteristic. If an additional load of 6 MW is added then frequency will be ___________
a) 50.25
b) 40.75
c) 49.75
d) 48.75
Answer: a
Explanation: power-systems-questions-answers-switchgear-protection-3-q11
power-systems-questions-answers-switchgear-protection-3-q11-diagram
power-systems-questions-answers-switchgear-protection-3-q11-exp
∆=0.25
Hence the resultant frequency will be 50.25 Hz.
This set of Tough Power Systems Questions and Answers focuses on “Switchgear and Protection – 4”.
1. An isolated generator connected to a turbine with its continuous maximum power of 20 MW, 50 Hz. Generator connected with two loads of 8 MW, each operate at 50 Hz.. Generator has 5% droop characteristic. If an additional load of 6 MW is added then the change in the frequency will be ____________
a) 0.25
b) 0.75
c) 0.5
d) 1
Answer: a
tough-power-systems-questions-answers-q1
2. For the given system the Ybus matrix is show below.
power-systems-questions-answers-switchgear-protection-4-q2-dia
power-systems-questions-answers-switchgear-protection-4-q3
d) None of the mentioned
Answer: a
Explanation: Y11=j2+ = 1.8j
Y12=- = 0.2j; Y13=0
Hence option ‘a’ is most applicable.
3. If short TL is delivering a lagging power factor load, sending end p.f. would be ________
a) (V r cosФ r +IR)/Vs
b) (V r cosФ r +IRsinФ r )/Vs
c) (V r sinФ r +IR)/V s
d) (V s sinФr+IRcosФr)/V s
Answer: a
Explanation: The phasor diagram is given below
power-systems-questions-answers-switchgear-protection-4-q3-dia
4. If all the sequence voltages at the fault point in a power system are equal, then fault is __________
a) LLG fault
b) LG fault
c) Three phase to ground fault
d) Line to Line fault
Answer: a
Explanation: It is LLG fault.
5. The below mentioned graph is a recorded data of the voltage fluctuation of the network, then it can be concluded that these faults are __________
power-systems-questions-answers-switchgear-protection-4-q5
a) L-G
b) A three phase motor short
c) Feeder fault
d) Any of the mentioned
Answer: a
Explanation: The sudden dip is the LG fault in the graph as the dips are not very large and the system is maintaining its stability.
6. The inertia constant of two groups of machines which do not swing together are 4 and 20 MJ/MVA, the equivalent inertia constant of the system is _________
a) 2.85
b) 14
c) 6
d) 12
Answer: a
Explanation: For the incoherent system, the equivalent inertia = H 1 H 2 /(H 1 +H 2 ).
7. A fault current of 1500A passing through the primary side of a 400/5 CT. On the secondary side an inverse time over current relay is connected whose current setting is 75%, the plug setting is __________
a) 5
b) 3.75
c) 6
d) 4
Answer: a
power-systems-questions-answers-switchgear-protection-4-q7
8. The three phase line is working at 50 Hz with conductors rearranged as shown. The Cph of TL at 132 kV is ___________
power-systems-questions-answers-switchgear-protection-4-q8
a) 8.75*10 -9
b) 8.75*10 -12
c) 26.2*10 -12
d) 26.2*10 -9
Answer: a
power-systems-questions-answers-switchgear-protection-4-q8-1
9. For a 100 MVA, 11 kV three phase Alternator observes a three phase fault at terminals of it. If the fault current is 2000 A, the pu value of positive sequence reactance ______
a) 2.62
b) 0.46
c) 1.31
d) 0.92
Answer: a
Explanation: PU fault current = 2000/5248.63 = 0.381 pu
0.381 = 1/X
X= 1/0.381 =2.62 pu.
10. A lossless TL having SIL of 3000 MW is provided with uniform distributed series capacitance compensation of 25% and shunt compensation of 30% then the SIL of compensated TL will be _______________
a) 3949.9
b) 3289
c) 2784.9
d) 2877.6
Answer: a
Explanation: SIL=(V 2 )/Z
SIL α 1/Z
Zcomp = Zs√/))
Kse = 0.25; Klsh = 0; Kcsh = 0.3,
Zcomp =0.7595
SILcomp = 0.7595*3000 = 3949.96 MVA.
11. A lossless TL having SIL of 3000 MW is provided with uniform distributed series capacitance compensation of 25% and shunt compensation of 30% then the compensated impedance of TL will be ____________
a) 0.7595
b) 2.88
c) 0.647
d) 3.27
Answer: a
Explanation: SIL=(V 2 )/Z
SIL α 1/Z
Zcomp = Zs√/))
Kse = 0.25; Klsh = 0; Kcsh = 0.3,
Zcomp =0.7595.
