Power Systems MCQ Set 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
Answer: d [Reason:] 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
Answer: c [Reason:] 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
Answer: d [Reason:] 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
Answer: b [Reason:] 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
Answer: c [Reason:] 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
Answer: d [Reason:] 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
Answer: b [Reason:] 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
Answer: c [Reason:] The series inductance and resistance of short transmission lines are taken as lumped. This makes the performance analysis easy.
Power Systems MCQ Set 2
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
Answer: a [Reason:] 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
Answer: a [Reason:] 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
Answer: d [Reason:] All are types of DC link.
4. (i) Monopolar DC link has one energised conductor of positive polarity.
(ii) It was ground as return path
Opt the most appropriate.
a) (i) is False & (ii) is True
b) (i) is True & (ii) is True
c) Both are false
d) (i) is True & (ii) is False
Answer
Answer: a [Reason:] Negative polarity is preferred on OH lines due to less radio interference.
5. (i) Bipolar link has two conductors
(ii) Both conductors have same magnitude of voltage.
a) (i) is False & (ii) is True
b) (i) is True & (ii) is True
c) Both are false
d) (i) is True & (ii) is False
Answer
Answer: b [Reason:] 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
Answer: b [Reason:] 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
Answer: a [Reason:] 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
Answer: a [Reason:] 50% of rated power can be supplied.
9. The overvoltage that occur mainly under converter stations are due to ___
(i) Lightening and switching overvoltage
(ii) Transients produced in conductors
(iii) Overvoltage due to fault clearing
Choose the correct option.
a) (i), (ii), (iii)
b) (ii), (iii)
c) (iii)
d) (i), (ii)
Answer
Answer: a [Reason:] All the statements are correct.
10. Insulator capacitance is does not play significant role in HVDC lines
a) True
b) False
Answer
Answer: a [Reason:] There is no capacitive current which flows in HVDC link.
Power Systems MCQ Set 3
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
Answer: a [Reason:] 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
Answer: a [Reason:] 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/(33*5√3 ) = 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
Answer: a [Reason:] 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
Answer: d [Reason:] 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
Answer: a [Reason:] The primary CT current for the relay operation = 1.5*1000/5 = 300 A
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
Answer: b [Reason:] The primary CT current for the relay operation = 1.5*1000/5 = 300 A
% winding unprotected = (Is*RV*100%)
= (300*5√3)/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
Answer: a [Reason:] % 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
Answer: a [Reason:] 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
Answer: d [Reason:] 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
Answer: b [Reason:] 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
Answer: a [Reason:] The carrier frequency has to be high in the case of carrier-current-pilot scheme.
Power Systems MCQ Set 4
1. The receiving end active power for a short transmission line is (where the angles have their usual meanings)
Answer
Answer: a [Reason:] Receiving end active power for a short transmission line is
2. The receiving end reactive power for a short transmission line is (where the angles have their usual meanings)
Answer
Answer: c [Reason:] Receiving end reactive power for a short transmission line is
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
Answer
Answer: a [Reason:] The sending end active power is 
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
Answer
Answer: d [Reason:] The sending end reactive power is 
5. The simplified ABCD representation of a 40 km transmission line is best given as
Answer
Answer: a [Reason:] From the given length, it is a short TL. Hence,
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
Answer
Answer: a [Reason:] From the given length, it is a short TL. Hence,
7. If it is tried to represent the active and reactive power on a circle, then the radius would be
Answer
Answer: a [Reason:] 
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
Answer: c [Reason:] Maximum power occurs for β=δ.
9. The maximum real active power delivered to the load is defined most accurately by
Answer
Answer: a [Reason:] The maximum real active power delivered to the load is 
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
Answer: a [Reason:] 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
Answer: a [Reason:] 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 ’?’.
Vs = ?*Vr+B*Ir
Is = C*Vr+D*Ir
a) 1+YZ
b) Z
c) Y
d) 1
Answer
Answer: a [Reason:] Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.
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 ’?’.
Vs = A*Vr+?*Ir
Is = C*Vr+D*Ir
a) 1+YZ
b) Z
c) Y
d) 1
Answer
Answer: b [Reason:] Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.
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 ’?’.
Vs = A*Vr+B*Ir
Is = ?*Vr+D*Ir
a) 1+YZ
b) Z
c) Y
d) 1
Answer
Answer: c [Reason:] Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.
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 ’?’.
Vs = A*Vr+B*Ir
Is = C*Vr+?*Ir
a) 1+YZ
b) Z
c) Y
d) 1
Answer
Answer: d [Reason:] Using KVL to the line diagram,
Vs = (1+YZ)*Vr+Z*Ir
Is = Y*Vr+Ir.
Power Systems MCQ Set 5
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
Answer: d [Reason:] 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
Answer: a [Reason:] 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
Answer: a [Reason:] 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
Answer: d [Reason:] An insulator should not have high water retention capability.
5. Consider the two statements and choose the options.
(i) Transmission of electrical power by dc is economical than with the ac
(ii) In case of dc transmission, there is no charging current which contributes to continuous load.
a) (i) and (ii) are true
b) (i) is only true
c) (ii) is only true
d) (i) and (ii) are false
Answer
Answer: a [Reason:] 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
Answer: a [Reason:] 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
Answer: a [Reason:] 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
Answer: b [Reason:] 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
Answer: a [Reason:] 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
Answer: a [Reason:] Because metal sheathed core has greater core to core thickness for a given diameter.
Power Systems MCQ Set 6
1. Single core cables for AC systems are not provided with armouring.
a) True
b) False
Answer
Answer: a [Reason:] 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
Answer: a [Reason:] 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 ____
Answer
Answer: a [Reason:] The electric field intensity,
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 _____
Answer
Answer: a [Reason:] The maximum stress will occur at the surface of the conductor such that x(min) = 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 ________
Answer
Answer: b [Reason:] The minimum stress will occur at the outermost surface of the conductor such that x(max) = 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
Answer: a [Reason:] The maximum stress will occur at the surface of the conductor such that x(min) = radius of core.
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) (R/r)2
Answer
Answer: a
8. The condition at which the minimized dielectric stress condition (R/r) will take place is ________
a) 2.7188
b) 0.7188
c) 1/2.7188
d) 2.71882
Answer
Answer: a
9. Grading of the cables is performed in order to achieve ______
(i) uniform stress
(ii) reduction in quantity of insulation
(iii) reduction in quality of insulation
a) (i), (ii)
b) (ii)
c) (i),(iii)
d) (ii), (iii)
Answer
Answer: a [Reason:] 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 _______ (in ohms).
a) 13.33
b) 20
c) 120
d) 40
Answer
Answer: a [Reason:] 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 ___(in degrees).
a) 15
b) 7.5
c) 20
d) 4.9
Answer
Answer: a [Reason:] Dielectric loss = ωCV2 tanδ
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) ωCV2 tanδ
b) ωCV2/tanδ
c) (tanδ/ωCV)2
d) ωCV2 tanδ2
Answer
Answer: a [Reason:] The Dielectric loss = ωCV2 tanδ for a cable.
13. The power losses occurring in the transmission cable has the relation with loss tangent angle as _____
a)
b)
c)
d) 
Answer
Answer: a [Reason:] The Dielectric loss = ωCV2 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 ______
Answer
Answer: a [Reason:] The generalized expression for the capacitance of the kth metal ring is,
C(k) = k*pin-to-earth/(n-k).
Power Systems MCQ Set 7
1. The zero sequence depiction of the unbalancing occurring at the terminals of the induction motor will be most likely _______
a)
b)
c)
d) 
Answer
Answer: a [Reason:] 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.
a) 1-a
b) a-1
c) 1
d) –a3
Answer
Answer: a [Reason:] Based on the phasor calculations the unknown vector is found using balanced condition of the three vectors A+B+C = 0 and 1+a+a2=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.
a) a
b) 0
c) a3
d) a4
Answer
Answer: a [Reason:] 1+a+ a2 = 0.
4. For a balanced three phase system having a vector representation as mentioned in the figure, complete the vector X and Y.
a) X=1-a2 ; Y=a2-a
b) bX=a2 -a; Y=1-a2
c) X=a2 -1; Y=1-a
d) X=a2 -1; Y=a-1
Answer
Answer: a [Reason:] 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.
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
Answer: a [Reason:] 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.
a) 1∠120°
b) 1∠30°
c) 1∠0°
d) 1∠-120°
Answer
Answer: a [Reason:] 1+a+ a2 = 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.
a) √3∠-30°
b) √3∠30°
c) √3∠-60°
d) √3∠90°
Answer
Answer: a [Reason:] Based on the phasor calculations the unknown vector is found using balanced condition of the three vectors A+B+C = 0 and 1+a+a2=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
Answer: a [Reason:] 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
Answer: b [Reason:] The zero sequence impedance does depend on the pitch of the armature coils of the synchronous machine.
