300+ REAL TIME Power Systems Objective Questions & Answers 2023

250+ TOP MCQs on Symmetrical Component Transformation – 1 and Answers

Power Systems Multiple Choice Questions on “Symmetrical Component Transformation – 1”.

1. 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
Clarification: Maximum power occurs for β=δ.

2. 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
Clarification: At θ=45°, ZVR and maximum VR coincide.

3. 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

250+ TOP MCQs on Switchgear and Protection – 2 and Answers

Advanced Power Systems Questions 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
Clarification: 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
Clarification: I_oc = i₁-i₂
I_RS = (i₁+i₂)/2
Relay will operate only if i_R > k(i₁+i₂)/2+i0
I₁ = 435/(500/5)
I₂ = 400/(500/5)
I_r = i₁-i₂ = 4.35-4.0 = 0.35 A
i₁+i₂ = 4.175 A
k(i₁+i₂)/2+i₀ = 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
Clarification: 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
Clarification: The fault setting implies that 20% of the neutral is unprotected.

5. The typical characteristic of the relay during loss of excitation is ____________
Answer: A
Clarification: The loss of excitation leads to a characteristic of the negative resistance offered.

6. The standard system fault characteristic of the relay is _____________
Answer: A
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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 _______________

Answer: A
Clarification: The line current in the delta side will rise from zero and star connection will have maximum current.

250+ TOP MCQs on Constituents of Steam Power Plant and Answers

Power Systems Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

250+ TOP MCQs on Economics of Power Generation and Answers

Power Systems Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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. (KWh supplied in a day)/24
B. {(KWh supplied in a day)/ 24 } × 365
C. {(KWh supplied in a month)/(30 x 24)
D. (KWh supplied in a year) / (24 × 365)

Answer: D
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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.

250+ TOP MCQs on Effect of Earth on the Three Phase Transmission Line Capacitance – 1 and Answers

Power Systems Multiple Choice Questions 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
Clarification: 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
Clarification: 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
Clarification: 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. √(L/C.
B. √LC
C. √(L+C.
D. √(C/L)

Answer: A
Clarification: The characteristic impedance for the lossless lines is given by √(L/C. 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
Clarification: 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
Clarification: 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

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
Clarification: 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

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
Clarification: It is used in protection of wires and cables for underground transmission.

250+ TOP MCQs on Symmetrical Component Transformation – 2 and Answers

Power Systems online quiz 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

A. 1+YZ, Z
B. Z,Y
C. Y, 1+YZ
D. 1+YZ, Y^-1+Z

Answer: A
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. 1+YZ, Z
B. Z,Y
C. 1+YZ, Y
D. 1+YZ, Y^-1+Z

Answer: C
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. 1+YZ, 1
B. 1+YZ, Z
C. Y, 1+YZ
D. 1+YZ, Y^-1+Z

Answer: A
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. 1+YZ, Z
B. Z,YZ+1
C. Z, 1+YZ
D. 1+YZ, Y^-1+Z

Answer: B
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. 1+YZ, Z
B. Z,Y
C. Y, 1+YZ
D. 1+YZ, Y^-1+Z

Answer: C
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. 1+YZ, Z
B. 1+ZY, 1
C. Y, 1+YZ
D. 1, 1+YZ

Answer: A
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. (1+YZ)* Z
B. 1+YZ* Z
C. Y*( 1+YZ)
D. (1+YZ)*Y^-1+Z

Answer: A
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. (1+YZ)* Y
B. (1+YZ)* Z
C. Y*( 1+YZ)
D. (1+YZ)*Y^-1+Z

Answer: A
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. (1+YZ)
B. (1+YZ)* Z
C. 1
D. 0

Answer: A
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*V_r+ Z*I_r
I_s = Y*V_r + I_r
AD = (1+YZ).

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

A. (1+YZ)
B. (1+YZ)* Z
C. Z
D. YZ

Answer: C
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. (1+YZ)
B. (1+YZ)* Z
C. 1
D. YZ

Answer: A
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. (1+YZ)
B. (1+YZ)* Z
C. Z
D. Y

Answer: A
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*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

A. Z-Y+YZ²
B. (1+YZ)* Z
C. 1+YZ+YZ²
D. 1-YZ+ZY²

Answer: A
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*V_r+Z*I_r
I_s = Y*V_r+I_r
AB-CD = (1+YZ)*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

A. Z-Y+YZ²
B. (1+YZ)* Z
C. YZ+YZ²
D. 1

Answer: D
Clarification: Using KVL to the line diagram,
V_s = (1+YZ)*V_r+Z*I_r
I_s = Y*V_r+I_r
AD-BC = (1+YZ)-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

A. ZY+(YZ)²
B. (1+YZ)* Z
C. YZ+YZ²
D. 1-YZ+ZY²

Answer: A