All SGP MCQ

1.
Ionization in circuit breakers is facilitated by

a) Increase of field strength
b) Increase of mean free path
c) High temperature
d) All of these
Ans: (d)
2. Arc interruption is done by

a) High resistance interrupon
b) Low resistance interrupon
c) Both (a) and (b)
d) None of these
Ans: (c)
3. Part of circuit breaker helpful in breaking the current is

a) Trip Coil
b) Contacts
c) Handle
d) Medium
Ans: (b)
4. Desired tripping of a circuit breaker is

a) Manually
b) Automacally
c) That it should give warning
d) None of these
Ans: (b)
5. Arcing time is the time between

a) Separaon of circuit breaker and exncon of arc
b) Separaon of circuit breaker and rise of recovery voltage
c) Normal current interrupon and arc exncon
d) None of these
Ans: (a)
6. For single frequency transients, ratio of peak restriking voltage to time

between voltage zero
and peak voltage is called
a) Restriking voltage
b) Recovery voltage
c) Rate of rise restriking voltage
d) Acve recovery voltage
Ans: (c)
7. Time between energisation of trip coil and separation of contacts is called

a) Closing me
b) Opening me
c) Both (a) and (b)
d) None of these
Ans: (d)
8. In circuit breaker, to facilitate arc quenching, dielectric strength can be

increased by
a) Lengthening of the gap
b) Cooling
c) Blast effect
d) All of these
Ans: (d)
9. Rate of rise restriking voltage depends upon

a) Acve recovery voltage
b) Natural frequency of oscillaons
c) Both (a) and (b)
d) Rang of circuit breaker
Ans: (c)
10. An ideal circuit breaker should offer

a) Zero & infinite impedance before & aer interrupon respecvely
b) Infinity & zero impedance before & aer interrupon respecvely
c) Equal impedance before & aer interrupon
d) None of these
Ans: (a)
11. Interrupting a low inductive current may lead to

a) Very high restriking voltage
b) Very high current
c) Rupture of circuit breaker
d) Current chopping
Ans: (d)
12. Instantaneous voltage in a circuit breaker depends upon

b) Rate of rise restriking voltage
c) Power factor
d) Frequency
Ans: (c)
13. Current chopping can be avoided by

a) Resistance switching
b) Inducve switching
c) Capacive switching
d) Diode switching
Ans: (a)
14. Recovery voltage is the value of the r.m.s. voltage that re-appears across the
poles of a
circuit breaker before
b) Final arc disncon
c) Rise of voltage
d) All of these
Ans: (b)
15. Time between separation of contacts and energisation of trip coil is called
a) Opening time
b) Closing time
c) Arching time
d) Decaying time
Ans: (a)
16. Which of the following is not a protective gear?

a) Fuse
b) Circuit breaker
c) Relay
d) None of these
Ans: (d)
17. Difficulty of performing the circuit breaking operation is a function of

a) Circuit voltage
b) Magnitude of the current
c) Electrical constants of the circuit
d) None of these
Ans: (c)
18. When contacts of circuit breaker opens

a) Arc is produced
b) Voltage rises
c) Breaker fails
d) Arc chamber is broken
Ans: (a)
19. A.C. air break circuit breakers are used for

a) Very high voltage
b) Very low voltage
c) Medium voltage
d) Medium and low voltage
Ans: (d)
20. Quantity of oil in bulk oil circuit breakers increases with

a) Decrease in voltage
b) Increase in voltage
c) Pressure of arc
d) Mechanical stresses
Ans: (b)
21. Air blast circuit breakers are preferred for

a) Short duty
b) Intermient duty
c) Repeated duty
d) All of these
Ans: (c)
22. Rating of circuit breaker depends upon

a) Breaking capacity
b) Making capacity
c) Short me capacity
d) All of these
Ans: (d)
23. Phenomenon of arc interruption takes place at

a) Zero voltage
b) Zero current
c) High current
d) High voltage
Ans: (b)
24. Symmetrical breaking current is

a) Peak value of a.c. component
b) Average value of a.c. component
c) R.m.s. value of a.c. component
d) All of these
Ans: (c)
25. Over voltage may be due to

a) Lightning impulse waveform
b) 50 Hz a.c.
c) Peak value of 50 Hz a.c.
d) All of these
Ans: (d)
26. In vacuum breakers, current wave

a) Reaches its maximum value
b) Aains its r.m.s. value
c) Is chopped
d) Aains its average value
Ans: (c)
27. In oil circuit breakers, dielectric strength of oil should be

a) High
b) Low
c) Medium
d) None of these
Ans: (a)
28. Main disadvantage (s) of oil circuit breaker is that it

a) Is easily inflammable
b) May from an explosive mixture with air
c) Requires maintenance
d) All of these
Ans: (d)
29. Breaker should adjust itself to

a) Fault magnitude and me
b) Increased arc and me of quenching
c) R R R V
d) None of these
Ans: (a)
30. At higher currents, the switchgear exhibit

a) Corona effect
b) Skin effect
c) Mechanical stresses
d) Poor regulaon
Ans: (b)
31. Plain circuit breaker can’t be used for voltage above

a) 400 V
b) 3.3 kV
c) 11 kV
d) 33 kV
Ans: (c)
SHAHAJIRAO PATIL VIKAS PRATISHTHAN
S. B. PATIL COLLEGE OF ENGINEERING, INDAPUR, DIST: PUNE.
DEPARTMENT OF ELCTRICAL ENGINEERING
ACA – R Academic Year: 2019 -20

Rev : 01 MULTI CHOICE QUESTIONS
Semester: II
Date: 03.07.2017
Date:14/03/2020
Ref: SPVP/SBPCOE/ELECT/2019-20/F22
Division/Class: BE Sub: switchgear and protection Subject Teacher: Prof. T.V. Deokar
Ques.1. The main function of a fuse is to

1. Protect the line
2. Open the circuit
3. Prevent excessive currents
4. None of the above
Answer.3. Prevent Excessive current
Ques.2. On which of the following routine tests are conducted?

1. Oil circuit breakers
2. Air blast circuit breakers
3. Minimum oil circuit breakers
4. All of the above
Answer.4. All of the above
Ques.3. SF6 gas

1. Is yellow in color
2. Is lighter than air
3. Is nontoxic
4. Has pungent small
Answer.3. Is nontoxic
Ques.4. The arcing contacts in a circuit breaker are made of

1. Copper tungsten alloy
2. Porcelain
3. Electrolytic copper
4. Aluminum alloy
Answer.1. Copper tungsten alloy

Ques.5. Which of the following medium is employed for the extinction of arc in air circuit
breaker?
1. Water
2. Oil
3. Air
4. SF6
Answer.3. Air
Ques.6. With which of the following, a circuit breaker must be equipped for remote
operation?
1. Inverse time trip
2. Time-delay trip
3. Shunt trip
4. All of the above
Answer.3. Shunt trip
Ques.7. A protective device, which reduces the steepness of wavefront of a surge by

absorbing surge energy is called
1. Surge Diverters
2. Surge absorber
3. Switching surges
4. Earthing screen
Answer.2. Surge absorber
Ques.8. A thermal protection switch can protect against

1. Short-circuit
2. Temperature
3. Overload
4. Overvoltage
Answer.3. Overload
Ques.9. Arc in a circuit behaves as
1. A capacitive reactance
2. An inductive reactance
3. A resistance increasing with voltage rise across the arc
4. A resistance decreasing with voltage rise across the arc
Answer.3. A resistance increasing with voltage rise across the arc
Ques.10. The thermal circuit breaker has

1. Delayed trip action
2. Instantaneous trip action
3. Instantaneous short action
4. Any of the above
Answer.1. Delayed trip action
Ques.11. Relays can be designed to respond to changes in

1. Resistance, reactance or impedance
2. Voltage and current
3. Temperature
4. All of the above
Ques.12. Overload relays are of type.

1. Solid state
2. Thermal
3. Electromagnetic
4. All of the above

Ques.13. Thermal overload relays are used to protect the motor against over current due
to
1. Short-circuits
2. Heavy loads
3. Grounds.
4. All of the above
Answer.2. Heavy Loads
Ques.14. The magnetic circuit breaker has trip action.

1. Delayed
2. Instantaneous
3. Short
Answer.2. Instantaneous
Ques.15. D.C. shunt relays are made of

1. Few turns of thin wire
2. Few turns of thick wire
3. Many turns of thin wire
4. Many turns of thick wire
Answer.3. Many turns of thin wire
Ques.16. The function of the circuit breaker is

1. To safeguard the circuit
2. On and off the circuit
3. To save human life
4. None of these
Answer.1. To safeguard the circuit

Ques.17. In order that current should flow without causing excessive heating or voltage
drop, the
relay contacts should
1. Have low contact resistance
2. Be clean and smooth
3. Be of sufficient size and proper shape
4. Have all above properties
Answer.4. Have all above properties
Ques.18. Circuit breakers usually operate under

1. Transient state of short-circuit current
2. Sub-transient state of short-circuit current
3. The steady state of short-circuit current
4. After D.C. component has ceased
Answer.1. Transient state of short-circuit current
Ques.19. Circuit breakers are essentially

1. Current carrying contacts called electrodes
2. Arc extinguishers
3. Circuits to break the system
4. Transformers to isolate the two systems
Answer.1. Current carrying contacts called electrodes
Ques.20. The current zero interruption, in oil and air blast circuit breakers, is achieved by
1. Lengthening of the gap
2. Cooling and blast effect
3. Both 1 and 2
4. Deionizing the oil with forced air
Answer.3. Both 1 and 2

Ques.21. Air blast circuit breaker is used for
1. Overcurrent
2. Short duty
3. Intermittent duty
4. Repeated duty
Answer.4. Repeated duty
Ques.22. An efficient and well-designed protective relaying should have

1. Good selectivity and reliability
2. Economy and simplicity
3. High speed and selectivity
4. All of the above
Ques.23. The burden of a protective relay is the power

1. Required to operate the circuit breaker
2. Absorbed by the circuit of relay
3. Developed by the relay circuit
Answer.2. Absorbed by the circuit of relay
Ques.24. Directional relays are based on the flow of

1. Power
2. Current
3. Voltage Wave
Answer.1. Power
Ques.25. A differential relay measures the vector difference between
1. Two current
2. Two voltage
3. Two similar quantities
4. Any of the above
Answer.4. Any of the above
Ques.26. A transmission line is protected by

1. Time graded and current graded overcurrent protection
2. Distance Protection
3. Both 1 and 2
Ques.27. Large internal faults are protected by

1. Merz price percentage differential protection
2. Mho and ohm relays
3. Horn gaps and temperature relays
4. Earth fault and positive sequence relays
Answer.1. Merz price percentage differential protection
Ques.28. When a transmission line is energized, the wave that propagates on it is

1. Current wave only
2. Voltage wave only
3. Both 1 and 2
4. Power factor wave only

Ques.29. Protective relays are devices that detect abnormal conditions in electrical
circuits by measuring
1. Current during abnormal condition
2. Voltage during abnormal condition
3. Constantly the electrical quantities which differ during normal and abnormal
conditions
Answer.3. Constantly the electrical quantities which differ during normal and
abnormal condition
Ques.30. The voltage appearing across the contacts after the opening of the
circuit breaker is called _voltage.
1. Recovery
2. Surge
3. Operating
4. Arc
Answer.1. Recovery
Ques.31. Ionization in the circuit breaker is facilitated by

1. High temperature
2. The increase of mean free path
3. Increasing field strength
4. All of the above
Ques.32. The rated voltage of the circuit breaker is

1. RMS Phase to Phase Voltage
2. Average Phase to Phase Voltage
3. RMS Ground to phase voltage
4. RMS Phase to Phase Voltage
Answer.1. RMS Phase to Phase Voltage

Ques.33. A relay used on short transmission lines is
1. Reactance Relay
2. Mho’s Relay
3. Impedance Relay
4. None of these
Answer.1. Reactance Relay
Ques.34. The time interval which is passed in between the energization of the trip coil to
the instant of contact separation is called the
1. Opening Time
2. Closing Time
3. Delayed Time
Answer.1. Opening Time
Ques.35. Shunt capacitance is neglected while considering

1. Short transmission line
2. Medium transmission line
3. Long transmission line
4. Medium and long transmission lines
Answer.1. Short transmission line
Ques.36. The arc voltage produced in A.C. circuit breaker is always

1. In phase with the arc current
2. Lagging the arc current by 90°
3. Leading the arc current by 90°
Answer.1. In phase with the arc current

Ques.37. IDMT Relay stands for
1. Inverse Divide Minimum Time
2. Inverse Define Minimum Time
3. Inverse Definite Minimum Time
4. Inverse Differentiate Minimum time
Answer.3. Inverse Definite Minimum Time
Ques.38. Insulation resistance of high voltage circuit breakers is carried out when
1. The circuit breaker is open
2. The circuit breaker is closed
3. Any of the above
Answer.3. Any of the above
Ques.39. H.R.C. fuses provide the best protection against

1. Overload
2. Reverse current
3. Open-circuits
4. Short-circuits
Answer.4. Short-circuits
Ques.40. The ground wire should not be smaller than No copper.

1 2
. 4
2
.3 6
.4 1
. 0
Answer.4. 10
Ques.41. The delay fuses are used for the protection of
1. Motors
2. Power outlet circuit
3. Fluorescent lamps
4. Light circuits
Answer.1. Motors
Ques.42. Which of the following is the least expensive protection for overcurrent is a low
voltage system?
1. Rewire able fuse
2. Isolator
3. Oil circuit breaker
4. Air break circuit breaker
Answer.1. Rewire able fuse
Ques.43. Resistance grounding is used for voltage between

1. 33kV to 66kV
2. 2.2 kV to 33 kV
3. 3.3 kV to 11 kV
4. All of the above
Answer.2. 2.2 kV to 33 kV
Ques.44. The current zero interruption, in oil and air blast circuit breaker, is achieved by
1. Deionizing the oil with forced air
2. Lengthening of the gap or cooling the blast effect
3. Lengthening of the gap
4. Cooling of the blast effect
Answer.2. Lengthening of the gap or cooling the blast effect

Ques.45. In Railway applications circuit breaker is used.
1. SF6
2. Bulk oil
3. Minimum oil
4. Air Blast
Answer.4. Air Blast
Ques.46. MCB protects a circuit from

1. Short circuit
2. Over Load only
3. Both short circuit and overload
Answer.3. both short circuit and overload
Ques.47. Wave trap is used to trap waves of

1. Power frequencies
2. Higher frequencies entering generator or transformer units
3. Lower frequencies entering generator or transformer units
4. Medium frequencies entering generator or transformer units
Answer.2. Higher frequencies entering generator or transformer units
Ques.48. The underground neutral transmission system is not recommended because of

the system
1. Insulation being overstressed due to overvoltage
2. Insulation overstress may lead to failure and subsequent phase to phase faults
3. Being inadequately protected against ground fault
4. All of the above

Ques.49. The reflection coefficient at the open-circuited end of a transmission line
1. Zero
2. Infinity
3. Unity
Answer.3. Unity
Ques.50. For the protection of power station buildings against direct strokes the
requirements are
1. Interception
2. Interception and conduction
3. Interception, conduction, and dissipation
4. Interception, conduction, dissipation, and reflection
Answer.3. Interception, conduction, and dissipation
Ques.51. Which of the following is used for the measurement of the insulation resistance?
1. Megger
2. Wattmeter
3. Ammeter
4. Voltmeter
Answer.1. Megger
Ques.52. The interaction between a transmission line and the communication line is
minimized by
1. Transposing transmission as well as communication lines
2. Increasing the height of the transmission line tower
3. Increasing the distance between the two lines
4. All of the above

Ques.53. In order to switch-off and EHV circuit for maintenance, the following sequence
is adopted:
1. Open the circuit breaker, open the isolator, operate the earth switch
2. Operate the earth switch, open the isolator, open the circuit breaker
3. Open the isolator, operate the earth switch, open the circuit breaker
4. Open the isolator, open the circuit breaker, operate the earth switch
Answer.1. Open the circuit breaker, open the isolator, operate the earth switch
Ques.54. Which of the following statements is incorrect?

1. Station batteries are used to operate relay only
2. The lightning arresters have basically surged diverters
3. An impedance relay has maximum fault current when the fault occurs near the relay
4. A high-speed relay has an operation of 1 to 2 cycles
Answer.2. The lightning arresters have basically surged diverters
Ques.55. Discrimination between main and back up protection is provided by the use of
relays
1. Facts
2. Sensitive
3. Slow
Answer.3. Slow
Ques.56. Induction cup relay is operated due to changes in

1. Current
2. Voltage
3. Both 1 & 2
Answer.3. Both 1 & 2

Ques.57. A.C. network analyzer is used to solve problems of
1. Load flow
2. Load flow and short-circuit
3. Load flow and stability
4. Load flow, short-circuit and stability
Answer.4. Load flow, short-circuit and stability
Ques.58. Lightning arrester connected in a power system protect electrical equipment

from
1. Over-voltage due to indirect lightning stroke
2. Direct stroke of lightning
3. Frequency fluctuation
4. Overcurrent due to indirect lightning stroke
Answer.4. Over-voltage due to indirect lightning stroke
Ques.59. Short-circuit currents are due to

1. Single phase to ground faults
2. Phase to phase faults
3. Two-phase to ground faults
4. Three phase faults
5. Any of these
Answer.5. Any of these
Ques.60. In busbar protection what is the method of providing an earthed metal barrier
surrounding a bus throughout its length called?
1. Fault bus protection
2. Time graded Overcurrent protection
3. Distance protection
4. Differential protection
Answer.1. Fault bus protection

Ques.61. Bus coupler is very essential in the arrangement
1. Single bus
2. Double bus, double breaker
3. Main and transfer bus
4. All of the above
Answer.3. Main and transfer bus
Ques.62. For cost and safety, the outdoor substations are installed for voltages above
1. 11 kV
2. 33 kV
3. 60 kV
4. 110 kV
Answer.2. 33 kV
Ques.63. The short circuit in any winding of the transformer is the result of
1. Mechanical vibration
2. Insulation failure
3. Loose connection
4. Impulse voltage
Answer.4. Impulse voltage
Ques.64. A mho relay is used for protection of:

1. Protection of a transformer against external fault
2. Long Transmission Line
3. Protection of a transformer against all the internal faults and external fault
4. Medium Length lines
Answer.2. Long Transmission Line

Ques.65. For which of the following protection from negative sequence currents is
provided?
1. Generators
2. Motors
3. Transmission line
4. Transformers
Answer.1. Generators
Ques.66. A relay which measures impedance or a component of the impedance at the

relay location is known as
1. Induction Relay
2. Moving Coil Relay
3. IDMT Relay
4. Distance Relay
Answer.4. Distance Relay
Ques.67. Distance relays are generally

1. Mho relays
2. Reactance relays
3. Impedance relays
4. All of the above
Ques.68. For which of the following ratings of the transformer differential protection is
recommended?
1. Above 30 kVA
2. Equal to and above 5 MVA
3. Equal to and above 25 MVA
Answer.2. Equal to and above 5 MVA

Ques.69. A is used to measure the stator % winding temperature of the generator.
1. Thermocouple
2. Pyrometer
3. Resistance thermometer
4. Thermometer
Answer.4. Thermometer
Ques.70. The under voltage relay can be used for

1. Generators
2. Busbars
3. Motors
4. All of the above
Ques.71. The relay with inverse time is

1. Directly proportional to the square of fault current
2. Direct proportional to the of fault current
3. Inversely proportional to the of fault current
4. Inversely proportional to the square of fault current
Answer.3. Inversely proportional to the of fault current
Ques.72. When the fault current is 2000 A, for a relay setting of 50% with CT ratio 500/5,
the plug setting multiplier will be
1 1
.2 61
. 4
3 2
.4 8
.
Answer.4. 8
Ques.73. Which of the following devices will receive voltage surge first traveling on the
transmission line?
1. Lightning arresters
2. Relays
3. Step-down transformer
4. Switchgear
Answer.1. Lightning arresters
Ques.74. Which of the following parameter can be neglected for a short line?
1. Inductance
2. Capacitance
3. Resistance
4. Reactance
Answer.2. Capacitance
Ques.75. Series reactors should have

1. Low resistance
2. High resistance
3. Low impedance
4. High impedance
Answer.1. Low resistance
Ques.76. Which of the following circuit breakers has high reliability and minimum
maintenance?
1. Air blast circuit breakers
2. Circuit breaker with SF6 gas
3. Vacuum circuit breakers
4. Oil circuit breakers
Answer.2. Circuit breaker with SF6 gas

Ques.77. Arc in a circuit breaker is interrupted at
1. Zero current
2. Maximum current
3. Minimum current
4. Maximum voltage
Answer.1. Zero current
Ques.78. The transmission line has a reflection coefficient as one

1. Open circuit
2. Short-circuit
3. Long
Answer.1. Open circuit
Ques.79. What will be the reflection coefficient of the wave of the load connected to the
transmission line if surge impedance of the line is equal to load?
1. Zero
2. Unity
3. Infinity
Answer.1. Zero
Ques.80. A Buchholz relay is used for

1. Protection of a transformer against all internal faults.
2. Protection of a transformer against external faults.
3. Protection of a transformer against both internal and external faults.
4. Protection of induction motors.
Answer.1. Protection of a transformer against all internal faults

Ques.81. Overvoltage protection is recommended for
1. Hydro-electric generators
2. Steam turbine generators
3. Gas turbine generators
4. All of the above
Answer.1. Hydro-electric generators
Ques.82. In a thyrite lightning arrester the resistance

1. Decrease linearly with the applied voltage
2. Is high at low current and low at high current
3. Is low at low current and high at high current
4. Increase linearly with the applied voltage
Answer.2. Is high at low current and low at high current
Ques.83. Over fluxing protection is recommended for

1. Distribution transformer
2. Generator transformer of the power plant
3. Auto-transformer of the power plant
4. Station transformer of the power plant
Answer.2. Generator transformer of the power plant
Ques.84. Series capacitors are used to

1. Compensate for line inductive reactance
2. Compensate for line capacitive reactance
3. Improve line voltage
Answer.1. Compensate for line inductive reactance
Ques.85. Admittance relay is relay.

1. Impedance
2. Distance
3. Non-directional
Answer.2. Distance
Ques.86. The material used for fuse must have
1. The low melting point and high specific resistance
2. The low melting point and -low specific resistance
3. High melting point and low specific resistance
4. Low melting point and any specific resistance
Answer.2. the low melting point and low specific resistance
Ques.87. If the fault occurs near the impedance relay, the VI ratio will be
1. Constant for all distances
2. Lower than that of if the fault occurs away from the relay
3. Higher than that of if the fault occurs away from the relay
Answer.2. Lower than that of if the fault occurs away from the relay
Ques.88. The torque produced in induction type relay (shaded pole structure) is
1. Inversely proportional to the current
2. Inversely proportional to the square of the current
3. Proportional to the current
4. Proportional to the square of the current
Answer.4. Proportional to the square of the current
Ques.89. The steady-state stability of the power system can be increased by

1. Connecting lines in parallel
2. Connecting lines in series
3. Using machines of high impedance
4. Reducing the excitation of machines
Answer.1. Connecting lines in parallel

Ques.90. Stability of a system is not affected by
1. Reactance of Line
2. Losses
3. Reactance of generator
4. Output Torque
Answer.1. Reactance of line
Ques.91. The following statement is associated with the Buchholz relay is not true
1. It is a gas actuated device
2. It is a current operative device
3. It is placed between the transformer tank and the conservator
4. It causes alarm for minor fault and tripping for major fault
Answer.2. It is a current operative device
Ques.92. A fuse is connected

1. In series with the circuit
2. In parallel with the circuit
3. Either in series or in parallel with circuit
Answer.1. In series with the circuit
Ques.93. H.R.C. fuse, as compared to a rewirable fuse, has

1. No aging effect
2. High speed of operation
3. High rupturing capacity
4. All of the above

Ques.94. The fuse rating is expressed in terms of
1. Current
2. Voltage
3. VAR
4. KVA
Answer.1. Current
Ques.95. Which one of the given fuse is bigger?

1. DC
2. AC
3. DC or AC
4. Both have same fuse size
Answer.1. DC
Ques.96. MCB protects a circuit from

1. Short circuit
2. Over Load only
3. Both short circuit and overload
Answer.3. Both short circuit and overload
Ques.97.In which of the following equipment, current rating is not necessary?

1. Circuit breaker
2. Relay
3. Isolator
4. Load break switch
Answer.3. Isolator
Ques.98. A fuse in a motor circuit provides protection against

1. Overload
2. Short-circuit
3. Open circuit, short-circuit and overload
Answer.2. Short-circuit
Ques.99. Which of the following fuse is very fast in operation?
1. KitKat fuse
2. Semiconductor Fuse
3. Cartridge fuse
4. High rupturing capacity type
Answer.2. Semiconductor Fuse
Ques.100. A fuse is never inserted in

1. Neutral wire
2. Negative of D.C. circuit
3. Positive of D.C. circuit
4. Phase line
Answer.1. Neutral wire
Ques.101. What is / are the main disadvantage of using oil as the quenching medium in
the circuit breakers?
a. Need periodical replacement.
b. Risk of formation of explosive mixture with air.
c. Possibility of causing fire hazards.
d. All of the above.
ANSWER: All of the above.
Ques.102. a three phases, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3s. What is
its symmetrical breaking current?
a. 1200 A
b. 3600 A
c. 35 kA
d. 104.8 kA
ANSWER: 35 kA
Ques.103. A thermal protection switch provides protection against what?
a. Overload
b. Temperature
c. Short circuit
d. Over voltage
ANSWER: Overload
Ques.104. Which of the following circuit breakers is used for the railway electrification?
a. Air blast circuit breaker
b. SF6 circuit breaker
c. Bulk oil circuit breaker
d. Minimum oil circuit breaker
ANSWER: Air blast circuit breaker
Ques.105. Which circuit breaker is preferred to be installed in extra high voltage AC

system?
a. Bulk oil type circuit breaker
b. Air blast circuit breaker
c. SF6 circuit breaker
d. Vacuum circuit breaker
ANSWER: SF6 circuit breaker
Ques.106. Which among these circuit breakers produce the least arc energy?
a. Plain oil
b. Minimum oil
c. Air blast
d. Air break
ANSWER: Air blast

Ques.107. The rating of the circuit breaker is usually determined on the basis of
fault.
a. Symmetrical
b. Line to line
c. Single line to ground
d. Double line to ground
ANSWER: Symmetrical
Ques.108. Which of the following circuit breaker is highly reliable and has a least
maintenance?
a. Oil circuit breakers
b. Air blast
c. Vacuum circuit breakers
d. SF6 circuit breakers
ANSWER: SF6 circuit breakers
Ques.109. Circuit breakers usually operate under

a. Steady short circuit current
b. Sub transient state of short circuit current
c. Transient state of short circuit current
d. None of these
ANSWER: Sub transient state of short circuit current
Ques.110. What is the making capacity of the circuit breaker?

a. Less than the asymmetrical breaking capacity of the breaker
b. Greater than the asymmetrical breaking capacity of the breaker
c. Equal to the asymmetrical breaking capacity of the breaker
d. Equal to the symmetrical breaking capacity of the breaker
ANSWER: Greater than the asymmetrical breaking capacity of the breaker

Ques.111. A three phase circuit breaker is rated 2000 MVA, 33 kV. What will be its making
current?
a. 35 kA
b. 49 kA
c. 70 kA
d. 89 kA
ANSWER: 89 kA
Ques.112. The breaking capacity of a three phase circuit breaker is given by

a. Service line voltage * rated symmetrical current in amperes * 10-6 MVA
b. √3 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA
c. 1.1* Service line voltage * rated symmetrical current in amperes * 10-6 MVA
d. √2 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA
ANSWER: √3 * Service line voltage * rated symmetrical current in amperes * 10-6

MVA
Ques.113. Which of the following circuit breakers has the lowest operating voltage?
a. SF6 circuit breaker
b. Air break
c. Air blast
d. Minimum oil circuit breaker
ANSWER: Air break
Ques.114. What is the making to breaking current ratio for an extra high voltage circuit
breaker?
a. More than 1
b. Equal to 1
c. Less than 1
d. A negative value
ANSWER: More than 1
Ques.115. Why is an isolator installed?
a. To isolate one portion of the circuit from another
b. As an substitute for the circuit breaker
c. It used on either sides of the circuit breaker
d. Both (a) and (c)
e. None of these
ANSWER: To isolate one portion of the circuit from another
Ques.115. For which among the following the current ratings are not required?
a. Circuit breakers
b. Relays
c. Isolators
d. Load break switch
ANSWER: Isolators
Ques.116. The isolators used in the transmission lines are capable of breaking
a. Fault current
b. No current
c. Charging current
d. Load current
ANSWER: Charging current
Ques.117. Why are the isolators
used?
a. Break abnormal current
b. Making under fault conditions
c. Breaking the circuit under no load condition
d. None of the above
ANSWER: Breaking the circuit under no load condition

Ques.118. What is the major cause of the failure of the circuit breaker?
a. Trip circuit open
b. Trip latch defective
c. Spring defective
d. All of these
ANSWER: All of these
Ques.119. What is the purpose of back up protection?

a. To increase the speed
b. To increase the reach
c. To leave no blind spot
d. To guard against failure of primary
ANSWER: To guard against failure of primary
Ques.120. What is the actuating quantity for the relays?

a. Magnitude
b. Frequency
c. Phase angle
d. All of these
Ques.121. Protective relays can be designed to respond to .

a. Light intensity, impedance
b. Temperature, resistance, reactance
c. Voltage and current
d. All of these
Ques.122. On what factor does the operating speed of the relay depend?
a. Rate of flux built up
b. Armature core air gap
c. Spring tension
d. All of these
Ques.123. Plug setting of a electromagnetic relay can be altered by varying

a. Number of ampere turns
b. Air gap of magnetic path
c. Adjustable back stop
d. None of these
ANSWER: Number of ampere turns
Ques.124.The most efficient torque producing actuating structure for the induction type
relays is
a. Shaded pole structure
b. Watt hour meter structure
c. Induction cup structure
d. Single induction loop structure
ANSWER: Induction cup structure
Ques.125. The least expensive protection for over current in low-voltage system is
A. Rewirable fuse
B. Isolator
C. Circuit breaker
D. Air-break switch
ANSWER: Rewirable fuse
Ques.126. Purpose of backup protection is

A. To increase the speed
B. To increase a reach
C. To leave no blind spot
D. To guard against failure of primary
ANSWER: To guard against failure of primary
Ques.127. We do not require any protection against prime mover failure in case of
A. Turbo generator sets
B. Hydro generator sets
C. Diesel engine driven alternators
D. Back pressure turbo generators
ANSWER: Turbo generator sets
Ques.128. For the protection of stator winding of an alternate against internal fault
involving ground the relay used is a
A. Biased differential relay
B. Directional over-current relay
C. Plain impedance relay
D. Buchholz relay
ANSWER: Biased differential relay
Ques.129. For the protection of a large squirrel cage induction motor against single
phase normally
A. An over-current relay is used
B. Differential relay is used
C. Directional relay is used
D. Negative sequence current sensitive relay is used
ANSWER: Negative sequence current sensitive relay is used
Ques.130. The most commonly used method for the protection of three phase feeder is
A. Time graded protection
B. Differential protection
C. Reverse power protection
D. None of the above
ANSWER: Differential protection

Ques.131.Which is the pilotless protection method for feeder line ?
A. Differential protection
B. Carrier current protection
C. Time credit protection
ANSWER: Carrier current protection
Ques.132.time graded protection of a radial feeder can be achieved by using

A. Definite time relay
B. Inverse time relay
C. Both definite and inverse time relays
ANSWER: Both definite and inverse time relays
Ques.133.Pilot-wire protection scheme is the most economical and provides high speed
relaying for
A. Short length of lines upto 15 km
B. Medium length of lives up to 60 km
C. Long length of lines up to 200 km
D. All of the above
ANSWER: Short length of lines upto 15 km
Ques.134.Problems associated with differential protection
is/are
A. Magnetising inrush current
B. Mismatching characteristics of CTs
C. Charge of ratio as a result of tapping
D. All of the above
ANSWER: All of the above

Ques.135.For the protection of transformers, harmonic restraint is used to guard against
A. Magnetising inrush current
B. Unbalanced operation
C. Lightning
D. Switching over-voltage
ANSWER: Magnetising inrush current
Ques.136.The types of faults that occur in electric motors are

A. Stator
B. Rotor
C. Overload
D. All of the above
Ques.137.The main function of under voltage protective device generally employed with
a motor starter is to
A. Open the supply circuit on failure of power supply
B. Control the motor voltage
C. Prevent the opening of supply circuit
ANSWER: Open the supply circuit on failure of power supply
Ques.138.The bias factor S in unit protection synchronous generators

A. Lies between .05 and .1 pu
B. Is less than .05 pu
C. Lies between .1 to .25 pu
D. Is greater than .025 pu
ANSWER: Lies between .05 and .1 pu
Ques.139.In a balanced voltage pilot wire protection scheme if the pilot circuit gets
opened, the relay will
A. Fail to trip on internal faults
B. Trip on full load
C. Trip instantaneously on external faults
ANSWER: Fail to trip on internal faults
Ques.140.In a balanced voltage pilot-wire protection scheme, if the pilot circuit gets short-
circuited, the relay will
A. Fail to trip on internal faults
B. Fail to trip on external faults
C. Trip on full load
D. Trip instantaneously
ANSWER: Trip on full load
Ques.141. The frequency of carrier in the carrier current pilot scheme is in the range of
A. 1 kHz to 10 kHz
B. 10 kHz to 25 kHz
C. 25 kHz to 50 kHz
D. 50 kHz to 500 kHz
ANSWER: 50 kHz to 500 kHz
Ques.142. The frequency of carrier transmitted by microwave pilot is in the range of

A. 1000 kHz to 1500 kHz
B. 2000 kHz to 5000 kHz
C. 900 kHz to 6000 kHz
D. 10000 kHz to 15000 kHz
ANSWER: 900 kHz to 6000 kHz
Ques.143. In carrier current protection the purpose of the wave trap is for
A. Trapping power frequency waves
B. Trapping high frequency waves entering into generators/ transformer unit
C. Both a and b
ANSWER: Trapping high frequency waves entering into generators/ transformer unit
Ques.144.As soon as a fault develops in a generator stator, it is essential to suppress field

excitation, otherwise
A. Terminal voltage will drop
B. It may lead to loss of synchronism
C. It will continue to supply power to the stator winding fault
D. All of the above
ANSWER: it will continue to supply power to the stator winding fault
Ques.145.Distance protection scheme is preferred over graded lime-lag over-current

protection in HV and EHV lines because
A. It is faster in operation
B. It is simple
C. It is cheaper in cost
D. All of the above
ANSWER: It is faster in operation
Ques.146. Requirements of protection power station buildings against direct strokes are
A. Interception
B. Conduction
C.. Dissipation
D. All of the above
Ques.147.The protection against direct lighting strokes and a high-voltage steep waves is
provided by
A. Ground wires
B. Lightning arresters
C. Lightning arresters and ground wires
D. Earthling of neutral
ANSWER: Lightning arresters and ground wires
Ques.148.For protection of rotating machines against lightning surge .............is

used
A. Lightning arrester
B. Capacitor
C. Combination of lightning arrester and a capacitor
D. Lightning conductor and arrester
ANSWER: Combination of lightning arrester and a capacitor
Ques.149. Outdoor switchgear is generally used for voltage beyond

A. 11 KV
B. 33 KV
C. 66 KV
D. 132 KV
ANSWER: 66 KV
Ques.150. In between the generating station and consumers a number of transformation

and switching stations exist, these are called the
A. Switchgears
B. Substations
C. Intermediate substations
D. Transformation stations
ANSWER: Sub-stations
What is switchgear
A. An apparatus used for switching, controlling and protecting the electrical circuits and equipments
B. It detects the faults only
C. It corrects the faults only
D. All of the above
ANSWER: D
A relay is said to be high speed relay if it operation time is

A. 1 to 2 cycles
B. 3 to 5 cycles
C. 2 to 3 cycles
D. 5 to 7 cycles
ANSWER: A
What is the purpose of back up protection

A. To increase the speed
B. To increase the reach
C. To leave no blind spot
D. To guard against failure of primary
ANSWER: D
What does protective relay provide

A. Provide additional safety to the circuit breaker in its operation
B. Close the contacts when the actuating quantity attains a certain predetermined value
C. Limit the arcing current during the circuit breaker operation
D. Earth or ground any stray voltage
ANSWER: B
What is the main advantage of using a fuse

A. Cheapest type of protection
B. Inverse time current characteristics
C. Current limiting effect under short circuit conditions
D. All of above
ANSWER: D
What is fusing factor

A. The ratio of current rating of the fuse to the minimum fusing current
B. The ratio of minimum fusing current to the current rating of the fuse
C. The ratio of maximum fusing current to the current rating of the fuse
D. The ratio of minimum fusing current to the voltage rating of the fuse
ANSWER: B
The main function of a fuse is to

A. Protect the line
B. Open the circuit
C. Prevent excessive currents
ANSWER: C
A thermal protection switch can protect against

A. Short-circuit
B. Temperature
C. Overload
D. Overvoltage
ANSWER: C
Relays can be designed to respond to changes in

A. Resistance, reactance or impedance
B. Voltage and current
C. Temperature
D. All of the above
ANSWER: D
Overload relays are of type

A. Solid state
B. Thermal
C. Electromagnetic
D. All of the above
ANSWER: D
An efficient and well designed protective relaying should have

A. Good selectivity and reliability
B. Economy and simplicity
C. High speed and selectivity
D. All of the above
ANSWER: D
Directional relays are based on the flow of

A. Power
B. Current
C. Voltage Wave
ANSWER: A
A differential relay measures the vector difference between

A. Two current
B. Two voltage
C. Two similar quantities
D. Any of the above
ANSWER: D
Protective relays are devices that detect abnormal conditions in electrical circuits by measuring
A. Current during abnormal condition
B. Voltage during abnormal condition
C. Constantly the electrical quantities which differ during normal and abnormal conditions
ANSWER: C
IDMT Relay stands for

A. Inverse Divide Minimum Time
B. Inverse Define Minimum Time
C. Inverse Definite Minimum Time
D. Inverse Differentiate Minimum time
ANSWER: C
H.R.C. fuses provide the best protection against
A. Overload
B. Reverse current
C. Open-circuits
D. Short-circuits
ANSWER: D
Which of the following is the least expensive protection for overcurrent is a low voltage system
A. Rewireable fuse
B. Isolator
C. Oil circuit breaker
D. Air break circuit breaker
ANSWER: A
MCB protects a circuit from

A. Short circuit
B. Over Load only
C. Both short circuit and overload
ANSWER: C
Discrimination between main and back up protection is provided by the use of relays
A. Facts
B. Sensitive
C. Slow
ANSWER: C
Induction cup relay is operated due to changes in

A. Current
B. Voltage
C. Both 1 & 2
ANSWER: C
When the fault current is 2000 A, for a relay setting of 50 percentage with CT ratio 500/5, the plug setting multiplier
will be
A. 16
B. 12
C. 4
D. 8
ANSWER: D
The material used for fuse must have

A. The low melting point and high specific resistance
B. The low melting point and low specific resistance
C. High melting point and low specific resistance
D. Low melting point and any specific resistance
ANSWER: B
The fuse rating is expressed in terms of

A. Current
B. Voltage
C. VAR
D. KVA
ANSWER: A
Trip circuit of protctuve relaying consists of

A. Trip coil and operating coil
B. CT with equipment to be protected only
C. Trip coil with DC or AC source
D. CT, Operating coil, trip circuit with AC or DC supply with CB
ANSWER: D
In Protective relaying, CT is connected in which manner

A. Parallel
B. Series
C. Series or Parallel
D. None of above
ANSWER: B
The main function of protctive relaying is

A. Alarming
B. Warning
C. Isolation of Circuit
D. None of above
ANSWER: C
Most dangarous fault on power system is

A. L-L
B. L-L-L
C. L-G
D. A and C
ANSWER: B
Maximum percentage of occuring in power sysstem is due to

A. L-L
B. L-L-L
C. L-G
D. A and B
ANSWER: C
Zones of protection has several zones_the squence of zone from source side is_
A. Generator-Transformer-busbar-Tx Line-distribution transformer-load
B. Generator-Transformer-busbar-Tx Line-busbar-distribution transformer-load
C. Transformer-busbar-Generator-Tx Line-distribution transformer-load
D. Transformer-Generator-busbar-Tx Line-distribution transformer-load
ANSWER: B
Primary and Back protection is nothing but_

A. Primary protection protects subsequent parts of Power system and back protection protects main parts of power s
stem
B. Primary protection is first line of defence and back up protection is second line of defence when primary protecti
n fails
C. Primary protection is second line of defence and back up protection is first line of defence when primary protecti
n fails
D. None of above
ANSWER: B
Torque equation of induction type of relay

A. T=K*phi1*phi2*Sin(theta)
B. T=K*phi1*phi2*Cos(theta)
C. T=phi1*phi2*Cos(theta)
D. T=phi1*phi2*Sin(theta)
ANSWER: A
The voltage appearing across the contacts after the opening of the circuit breaker is called voltage
A. Recovery
B. Surge
C. Operating
D. Arc
ANSWER: A
Ionization in the circuit breaker is facilitated by

A. High temperature
B. The increase of mean free path
C. Increasing field strength
D. All of the above
ANSWER: D
The current zero interruption, in oil and air blast circuit breaker, is achieved by
A. Deionizing the oil with forced air
B. Lengthening of the gap or cooling the blast effect
C. Lengthening of the gap
D. Cooling of the blast effect
ANSWER: B
Arc in a circuit breaker is interrupted at

A. Zero current
B. Maximum current
C. Minimum current
D. Maximum voltage
ANSWER: A
Ionization in circuit breaker is facilitated by

A. high temperature
B. increase of mean free path
C. increasing field strength
D. all of the above
ANSWER: D
Resistance switching in normally employed in

A. bulk oil breakers.
B. minimum oil breakers.
C. air blast circuit breaker.
D. SF6 circuit breaker
ANSWER: C
The stability of arc in vacuum depends on

A. The contact material only.
B. The circuit parameters only.
C. The contact materials and its vapour pressure.
D. Both (B) and (C)
ANSWER: D
A 50 Hz, 11 kV, 3 phase alternator with earthed neutral having a reactance of 3 ohms per phase and is connected to
bus bar through a circuit breaker, if the distributed capacitance upto CB between the phase and neutral is 0.01 MIC
OF. What is the frequency of oscillations?
A. 10000 Hz
B. 12500 Hz
C. 12628 Hz
D. 13265 Hz
ANSWER: C
When does the arc interruption in oil circuit breaker take place?
A. Contacts apart.
B. Voltages becomes zero
C. Current goes through zero
D. All of the above
ANSWER: C
To limit current chopping in vacuum circuit breakers, the contact material employed should have the properties of
A. Low conductivity and high vapour pressure.
B. Low conductivity and low vapour pressure.
C. High conductivity and high vapour pressure.
D. High conductivity and low vapour pressure
ANSWER: A
Why is the resistance switching used in a air blast circuit breaker?

A. Reduce the magnitude of fault current
B. Control the CB operating time
C. Damp out the fast transient AND reduce restriking voltage
D. Change the fault current power factor
ANSWER: C
CB circuit with L - C introducing a damping circuit. For the critical damping what is the value of resistance switchin
R?
A. ROOT(LC)
B. 0.5*ROOT(C/L)
C. 0.5*ROOT(L/C)
D. 2*PI*ROOT(L/C)
ANSWER: C
A 50 Hz, 11 kV, 3 phase alternator with earthed neutral having a reactance of 3 ohms per phase and is connected to
bus bar through a circuit breaker, if the distributed capacitance upto CB between the phase and neutral is 0.01 MIC
O FARADAY, What is the peak re striking voltage?
A. 18.36 kV
B. 17.96 kV
C. 15.96 kV
D. 12.65 kV
ANSWER: B
How is the restriking voltage CONSIDERED?

A. TRANSIENT VOLTAGE
B. PEAK VOLTAGE
C. RMS VOLTAGE
D. A AND B
ANSWER: D
Rate of rise of restriking voltage depend on ?

A. ype of circuit breaker.
B. Capacitance of the system.
C. Inductance of the system.
D. Both (B) and (C)
ANSWER: D
On what factor does the rate of rise of restriking voltage (RRRV) depend?
A. System voltage.
B. Circuit power factor only
C. Switching conditions
D. Both (B) and (C)
ANSWER: D
What is restriking voltage?

A. The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction.
B. The transient voltage that appears across the circuit breaker contacts at the end of arc extinction.
C. Both (a) and (b)
ANSWER: A
The resistance of an electric arc can be increased by

A. Increasing the concentration of ionised particles.
B. Reducing the arc length.
C. Splitting the arc.
D. Increasing the arc cross section
ANSWER: C
By using low resistance method for arc extension what is the value of arc resistance?
A. Arc resistance is zero.
B. Arc resistance is high
C. Arc resistance is low
D. Arc resistance is very high
ANSWER: C
What happens in the arc extinction using high resistance method?

A. Arc resistance is decreased with time.
B. Arc resistance is increased with time.
C. No change it remains same.
D. Arc resistance is kept zero
ANSWER: B
The arc resistance depends on which among the following factors?

A. Cross section of the arc.
B. Length of the arc.
C. Degree of ionization
D. All of the above
ANSWER: D
In Current chopping phenamenon the voltage across CB contact is when magnetising current is I
A. V=I*Root(L/C)
B. V=0.5*Root(L/C)
C. V=2*pi*Root(L/C)
D. V=I*Root(C/L)
ANSWER: A
Maximum value of restriking voltage

A. V=2*Vm
B. V= Vm
C. V=3*Vm
D. V=4*Vm
ANSWER: A
Maximum value of RRRV

A. V= 2*Vm
B. V= Vm*wn
C. V= 2*Vm*wn
D. V=2*wn
ANSWER: B
Value of critical resistance for no transient oscillations

A. R=0.5*root(L/C)
B. R=root(L/C)
C. R=0.5*root(C/L)
D. R=root(C/L)
ANSWER: A
SF6 gas
A. Is yellow in color
B. Is lighter than air
C. Is nontoxic
D. Has pungent small
ANSWER: C
The arcing contacts in a circuit breaker are made of

A. Copper tungsten alloy
B. Porcelain
C. Electrolytic copper
D. Aluminum alloy
ANSWER: A
Which of the following medium is employed for the extinction of arc in air circuit breaker?
A. Water
B. Oil
C. SF6
D. Air
ANSWER: D
The function of the circuit breaker is

A. On and off the circuit only
B. Make, Break and Carry the circuit
C. To save human life
D. None of these
ANSWER: B
The rated voltage of the circuit breaker is

A. RMS Phase to Phase Voltage
B. Average Phase to Phase Voltage
C. RMS Ground to phase voltage
D. RMS Phase to ground Voltage
ANSWER: A
The arc voltage produced in A.C. circuit breaker is always

A. In phase with the arc current
B. Lagging the arc current by 90฀
C. Leading the arc current by 90฀
ANSWER: A
What is the making capacity of the circuit breaker?

A. Less than the asymmetrical breaking capacity of the breaker
B. Greater than the asymmetrical breaking capacity of the breaker
C. Equal to the asymmetrical breaking capacity of the breaker
D. Equal to the symmetrical breaking capacity of the breaker
ANSWER: B
Circuit breakers usually operate under

A. transient state of short-circuit current
B. sub-transient state of short-circuit current
C. steady state of short-circuit current
D. after D.C. component has ceased
ANSWER: A
Which of the following circuit breaker is design for the least operating voltage?
A. Vacuum circuit breaker
B. Air circuit breaker
C. SF6 circuit breaker
D. Oil circuit breaker
ANSWER: B
Which of the following circuit breaker is design for the highest operating voltage?
A. Vacuum circuit breaker
B. Air blast circuit breaker
C. SF6 circuit breaker
D. Oil circuit breaker
ANSWER: B
Which circuit breaker has high reliability and negligible maintenance?

A. Air blast circuit breaker.
B. Oil circuit breaker.
C. SF6 circuit breaker.
D. Vacuum circuit breaker
ANSWER: C
Electrical Switchgear is consider as low voltage Switchgear if it is rated upto

A. 400 V
B. 1 kV
C. 11 kV
D. 33kV
ANSWER: B
A device which is used to protect an electric circuit from damage caused by over load or short circuit is
A. Wave trapper
B. CVT
C. circuit breaker
D. lighting arrester
ANSWER: C
An isolator is a device design to operates on

A. no load
B. normal condition
C. full load
D. none of the above
ANSWER: A
The breaking capacity of a fuse is

A. zero
B. small
C. high
D. infinite
ANSWER: B
A three phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3s. What is its symmetrical breaking current?
A. 1200 A
B. 3600 A
C. 35 kA
D. 104.8 kA
ANSWER: C
The making and breaking currents of a 3 phase ac circuit breakers in power systems are respectively in for
A. rms value, rms value

B. instantaneous value, rms value
C. rms value, instantaneous value
D. instantaneous value, instantaneous value
ANSWER: D
A three phase circuit breaker is rated 2000 MVA, 33 kV. What will be its making current?
A. 35 kA
B. 49 kA
C. 70 kA
D. 89 kA
ANSWER: D
What is the major cause of the failure of the circuit breaker?

A. Trip circuit open
B. Trip latch defective
C. Spring defective
D. All of these
ANSWER: D
The breaking capacity of a three phase circuit breaker is given by

A. Service line voltage * rated symmetrical current in amperes * 10-6 MVA
B. ROOT(3) * Service line voltage * rated symmetrical current in amperes * 10-6 MVA
C. 1.1* Service line voltage * rated symmetrical current in amperes * 10-6 MVA
D. ROOT(2) * Service line voltage * rated symmetrical current in amperes * 10-6 MVA
ANSWER: B
What is the normal pressure at which the SF6 gas is maintained in the closed position of the breaker?
A. 2 kg / cm2
B. 2.5 kg /cm2
C. 2.8 kg / cm2
D. 3 kg / cm2
ANSWER: C
During arc extinction SF6 gas gets converted to which among these?
A. Gets decomposed to SF4 and SF2
B. Gets decomposed to S and F
C. Gets reduced to SF6
D. Gets oxidized
ANSWER: A
Making currrent is times breaking current

A. 1.8
B. 2.55
C. 1.44
D. 1.55
ANSWER: B
Short-circuit currents are due to
A. Single phase to ground faultss
B. Phase to phase faults
C. Two-phase to ground faults
D. Any of these
ANSWER: D
Static relays are better than elctromechanical relays in

A. Cost, Size, external supply requiremnt, power consumption, Accuracy
B. Accuracy, Speed, Size, No effect of gravity, power consumption
C. Roubust operation, speed, no effect of temperature,size
D. None of above
ANSWER: A
Effect of Temperature on performance of static and electromechanical relay

A. No effect on static relay and effect on electromechanical relay
B. Effect on static relay and effect on electromechanical relay
C. Effect on static relay and No effect on electromechanical relay
D. No Effect on static relay and No effect on electromechanical relay
ANSWER: C
The function of transducer in static relay is to_

A. Sense the electrical signal
B. Show the electrical signal
C. sense and give the electrical signal to rectifier
D. Sense and give electrical signal to amplifier
ANSWER: C
The sequence of components in block diagram of static relay from soure side is
A. Rectifier-transducer-amplifier-trip cirucit-relay measuring circuit-output device
B. Transducer-Rectifier-amplifier-relay measuring circuit-output device-trip cirucit
C.Transducer-amplifier-relay measuring circuit-Rectifier-output device-trip cirucit
D.Transducer-Rectifier-relay measuring circuit-amplifier-output device-trip cirucit
ANSWER: D
Numerical relay has requires

A. Computer, Controller, S & H Circuit, Anti Alising filter only
B. CT/PT, Anti Alising filter, S & H Circuit, Multifexer, ADC, Computer, Controller
C. CT/PT, Anti Alising filter, S & H Circuit, Multifexer only
D. CT/PT, Multifexer, ADC, Computer, Controller only
ANSWER: B
Anti alising filter is used to

A. Rectify the signal
B. Smoothen the signal
C. Smoothen the signal for proper operation of S&H circuit
D. None of above
ANSWER: C
Equation of sampling theorem

A.w>=2*ws
B.w<=2*ws
C.w>=ws
D.w<=ws
ANSWER: A
PMU stands for

A. Phasor Motor Unit
B. Phasor Measurment Unit
C. Protection Measurment Unit
D. Protecton Motor Unit
ANSWER: B
Phasor Measurement Unit requires

A. GPS recevier, Modem, Antialising filter, Transducer, ADC, phase locked oscillator and microprocessor
B. GPS recevier, Modem, Antialising filter, Transducer, ADC, phase locked oscillator only
C. Antialising filter, Transducer, ADC, phase locked oscillator and microprocessor only
D. Antialising filter, GPS recevier, Modem and microprocessor only
ANSWER: A
Major percentage Faults in induction motor is due

A. Bearing faults
B. Stator Faults,
C. Rotor Faults
D. Other faults
ANSWER: A
Inter turn faults present in induction motor in

A. Stator winding only
B. Rotor winding only
C. both A and B
D. Lap winding
ANSWER: A
Major electrical faults present in induction motor in which winding

A. Stator winding only
B. Rotor winding only
C. both A and B
D. Lap winding
ANSWER: A
Abnormal conditions present in motor

A. Thermal overloading
B. Single Phasing
C. Short circuit faults and stalling of motor
D. All of above
ANSWER: D
Protections used against thermal overloading of induction motor are

A. Thermal Overload Relay, Inverse overcurrent Relay, MCB, Fuse
B. Thermal Overload Relay, Inverse overcurrent Relay, RTD based Relay, MCB
C. HRC or Rewirable Fuse, Differential Protection (motor generator Set), Instantaneous overcurrent relay, MCB
D. Thermal Overload Relay, Inverse overcurrent Relay, MCB, Fuse, Single Phase Preventer
ANSWER: B
Protections used against Short circuit faults in induction motor are
C. HRC or Rewirable Fuse, Differential Protection (motor generator Set), Instantaneous overcurrent
relay
D. Thermal Overload Relay, Inverse overcurrent Relay, MCB, Fuse, Single
Phase Preventer ANSWER: C
Protections used against Single phasing in induction motor are

C. Thermal overload Relay, Single Phase Preventer only
D. Thermal Overload Relay, Inverse overcurrent Relay, MCB, Fuse, Single
Phase Preventer ANSWER: C
Effect of single phasing in induction motor

A. Speed decreases, motor tries to stop or run-slow (stalling)
B. motor does not stall-stator & rotor will seriously overheat-because load will be shared by
remaining 2 phases
C. Only increase in temp
D. Speed decreases, motor tries to stop or run-slow, rotor will seriously overheat and
increase in temp ANSWER: D
Single phase preventor has following parts

A. NO/NC contacts, Negative sequence filter, ON/OFF buttons, Relay and main contctor
B. ON/OFF buttons, Relay and main contctor only
C. NO/NC contacts, Negative sequence filter, ON/OFF buttons only
D. NO/NC contacts, Negative sequence filter, ON/OFF buttons, Relay and main contctor with
energising coil ANSWER: D
General protection schemes used for induction motor are

A. MCB, Fuse, Thermal overload relay, IDMT relay
B. Circuit breaker, MCB, overload Relay
C. MCB, Fuse, Thermal overload relay, Instataneous O/c relay,differential relay(with
generator set) D.None of above
ANSWER: C
Maximum percentage of fault in induction motor is

A. L-L
B. L-G
C. L-L-G
D.
L
-
L
-
L
A
N
S
W
E
R
:
B
In a thermal relay, a bi-metal strip consists of two metal strips having different
A. thermal conductivity
B. efficient of expansion
C. specific heat
D. all
of the
above
ANS
WER:
B
SGP MCQS QUESTION BANK
1. Relay gets its operating energy

from- a.Transformer
b.Alternator
c.Overhead line
d. CT,PT
ANSWER:D
2. Which of the following circuit breakers is used for the railway electrification?
a. Air blast circuit breaker
b. SF6 circuit breaker
c. Bulk oil circuit breaker
d.Minimum oil circuit breaker
ANSWER: Air blast circuit breaker
3.Back up protection is needed for –

a.Over voltage
b.Short circuits
c.Over current
d.All of these
ANSWER:B
4. Which circuit breaker is preferred to be installed in extra high voltage AC system?

a. Bulk oil type circuit breaker
b. Air blast circuit breaker
c. SF6 circuit breaker
d.Vacuum circuit breaker
ANSWER: SF6 circuit breaker
5.Induction cup relays responds to –

a.Current
b.Power
c.Voltage
d.Impedance
ANSWER:D
6) Which among these circuit breakers produce the least arc energy?
a. Plain oil
b. Minimum oil
c. Air blast
d. Air break
ANSWER: C Air blast
7)Rating of circuit breaker depends upon-

Breaking capacity
Making capacity
Short time capacity
All of these
ANSWER:D
8) The rating of the circuit breaker is usually determined on the basis of fault.
a. Symmetrical
b. Line to line
c. Single line to ground
d.Double line to ground
ANSWER: Symmetrical
9) Which of the following circuit breaker is highly reliable and has a least maintenance?
a. Oil circuit breakers
b. Air blast
c. Vacuum circuit breakers
d.SF6 circuit breakers ANSWER:
SF6 circuit breakers
10)Phenomenon of arc interruption takes place at-

Zero voltage
Zero current
High Voltage
High Current
ANSWER:B
11)Effect of Arc Resistance and swing are perform by-

MHO
Impedance
reactance relay
none
ANSWER :B
12)In which relay having no effect on arc fault-
Impedance
reactance
MHO
Thermal overlod
ANSWER : B
13) Symmetrical breaking current is-
Symmetrical breaking
Average value of a.c. component
R.m.s. value of a.c. component
All of these
ANSWER:C
14) Non directional over current relay scheme is not suitable for-
Ring main and interconnected
Tie Scheme
Sectionlise
None of these
ANSWER :A
15) Circuit breakers usually operate under

a. Steady short circuit current
b. Sub transient state of short circuit current
c. Transient state of short circuit current
d. None of these
ANSWER: B Sub transient state of short circuit current
16) What is the making capacity of the circuit breaker?

a. Less than the asymmetrical breaking capacity of the breaker
b. Greater than the asymmetrical breaking capacity of the breaker
c. Equal to the asymmetrical breaking capacity of the breaker
d. Equal to the symmetrical breaking capacity of the breaker
ANSWER: B Greater than the asymmetrical breaking capacity of the breaker
17) The impedance of transmission line is proportion to

Distance
Length
Rated current
Rated Voltage
ANSWER : B
18) In oil circuit breakers, dielectric strength of oil should be-

High
Low
Medium
None
ANSWER:A
19) A three phase circuit breaker is rated 2000 MVA, 33 kV. What will be its making current?
a. 35 kA
b. 49 kA
c. 70 kA
d.89 kA
ANSWER: 89 kA
20) Plain circuit breaker can’t be used for voltage above-
400kv
3.3kv
66kv
11kv
ANSWER:D 11KV
21) The breaking capacity of a three phase circuit breaker is given by

a. Service line voltage * rated symmetrical current in amperes * 10-6 MVA
b. √3 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA
c. 1.1* Service line voltage * rated symmetrical current in amperes * 10-6 MVA
d. √2 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA
ANSWER: √3 * Service line voltage * rated symmetrical current in amperes * 10-

6 MVA
22) The earth fault protection of short and medium lines is used-
Quadrilateral relay
Electro magnetic
Electro mechanical
none
ANSWER : A
23) Part of circuit breaker helpful in breaking the current is-

Trip Coil
Contact
Handle
Medium
ANSWER:B
24) Assertion
(A): In comparison to making capacity of a circuit breaker its breaking
capacity is normally higher.
Reason (R): The breaking capacity of a CB is expressed as √3 * VI * 10-6 MVA
a. Both A and R are true and R is the correct explanation of A
b. Both A and R are true and R is not the explanation of A
c. A is true but R is false
d. A is false but R is true.
ANSWER: A is false but R is true.
25) It is a technology to improve situation and visibility within power system grids
is
WAM
PMU
PLCC
None
ANSWER : A
26) Arcing time is the time between-

Separation of circuit breaker and extinction of arc
Separation of circuit breaker and rise of recovery voltage
None of these
ANSWER:A
27) What is the making to breaking current ratio for an extra high voltage circuit breaker?
a. More than 1
b. Equal to 1
c. Less than 1
d.A negative value
ANSWER: More than 1
28) For single frequency transients, ratio of peak restriking voltage to time
between voltage zero and peak voltage is called-
Restriking voltage
Recovery voltage
RRRV
Active Recovery voltage
ANSWER:C RRRV
29) Arc resistance is given by-

2.9*10^4L/(If)^1.4
2.9*10^4L/(If)^1.6
2.5*10^4L/(If)^1.4
None
ANSWER: A
30) Why is an isolator installed?

a. To isolate one portion of the circuit from another
b. As an substitute for the circuit breaker
c. It used on either sides of the circuit breaker
d. Both (a) and (c)
e. None of these
ANSWER:A To isolate one portion of the circuit from another
31) Time graded principle is applicable where impedance between-

Feeder length is less
Feeder length is high
Feeder length is same
none
ANSWER :A
32) For which among the following the current ratings are not required?
a. Circuit breakers
b. Relays
c. Isolators
d.Load break switch
ANSWER: C- Isolators
33) The isolators used in the transmission lines are capable of breaking
a. Fault current
b. No current
c. Charging current
d. Load current
ANSWER:C- Charging current

34) Why are the isolators used?
a. Break abnormal current
b. Making under fault conditions
c. Breaking the circuit under no load condition
d. None of the above
ANSWER:C- Breaking the circuit under no load condition
35) What is the major cause of the failure of the circuit breaker?
a. Trip circuit open
b. Trip latch defective
c. Spring defective
d. All of these
ANSWER: D-All of these
36) SF6 gas is-

Is yellow in color
Is lighter than air
is nontoxic
Has pungent small
ANSWER:C
37) What is the purpose of back up protection?

a. To increase the speed
b. To increase the reach
c. To leave no blind spot
d.To guard against failure of primary ANSWER:
To guard against failure of primary
38) Rate of rise restriking voltage depends upon-

Active recovery voltage
Natural frequency of oscillations
Both (a) and (b)
Rating of circuit breaker
ANSWER: C
39 ) What is the actuating quantity for the relays?

a. Magnitude
b. Frequency
c. Phase angle
d. All of these
40) Protective relays can be designed to respond to .

d. All of these
41) On what factor does the operating speed of the relay depend?
c. Spring tension
d. All of these
42) Breaking capacity of a circuit

breaker is usually expressed in terms of
Volt
Ampere
MVA
MW
ANSWER:C -MVA
43) In impedance relay, current element torque should be-
Equal to voltage element torque
Greater than voltage element torque
Less than voltage element torque
None of these
ANSWER:B
44) Plug setting of a relay can be changed by changing

Air gap
Back up stop
Number of ampere turns
All of these
ANSWER:C
Instantaneous relay should operate within

0.0001 sec
0.001 sec
0.01 sec
0.1 sec
ANSWER :C
45) In the following figure, which component ensures the safety of the line from damage?
a. Relay
b. Circuit breaker
c. Bus bar
d.Current transformer
ANSWER: A-Relay
46) MHO relay is inherently a

Directional type
non Directional type
Unidirectional type
None of these
ANSWER :A
A three phase circuit breaker is rated 2000 MVA, 33 kV. What will be its making current?
35KA
49KA
65KA
89KA
ANSWER:D 89KA
47) For long tramsmission line,communication is possible two channels by-

PLC
PLCC
WAM
PMU
ANSWER : B
48) Protective relays can be designed to respond to .

d. All of these
ANSWER: D- All of these
49) The bus-bar zone .the purpose of protection includes …….&…..

Bus bar,isolating s/w,C.B
Transfomer,relay,CB
Relay,conductor,Transfomer
All of these
ANSWER : A
50)The measurement of electrical quantity is done by-
Stationary network
Moving N/W
Zig Zag
All of Above
ANSWER : A
51) Z=V/I in case of-

Distance or imdance relay
Diff.relay
Thermal overload
All of these
ANSWER : A
52) On what factor does the operating speed of the relay depend?
c. Spring tension
d. All of these
53) which relay is called computer base relay-

Static relay
Numerical relay
Impedence relay
Diff.relay
ANSWER : B
54) The low pass filter which filter out undesired frequency component is
Alliasing Filter
Aniti-aliasing Filter
PMU
Samplig
ANSWER : B
.
55) Proper sampling phenomenon represent in-
Wsm>/2Wsg
Wsm< 2Wsg
Wsm= 2Wsg
none of these
ANSWER : A
56) Loss of Excitation protectd by which device-
Offset MHO Relay
Admitance relay
Thermal overload
All of these
ANSWER : A
57) For protection of I.M from single phasing called-

DOL Starter
Revese phse sequence
1 phase preventor
None of these
ANSWER : C
58) Which device measure data up to 10 phasor and line frequency

WAM
PLC
PMU
PLCC
ANSWER : C
59) The diff.protection is based in current circlation principle is known as-
Bias Protection
% of diff.protection
overload
Merz prize
ANSWER : D
60) Incipient fault oil level resulting and decomposition oil protected by-
Buchholz relay
Thermal overload
Induction type
All of these
ANSWER : A
61) In the following figure, the tripping circuit is .
a. AC
b. DC
c. Either AC or DC
d. None of these
ANSWER: Either AC or DC
62) For 10MVA ,33KV/3.3kv power transformer wit delta star connecton obtain
CT ratio fo diff.protection scheme to circulated current of 400/ 5Ain pilot
wires.determine CT ratio of HT side
13.85
15.85
17.08
20
ANSWER : A
63) Harmonic restraint protected for-

Buchholz relay
Earth fault
icipient fault
Inrush current
ANSWER : D
64) Plug setting of a electromagnetic relay can be altered by varying

a. Number of ampere turns
b. Air gap of magnetic path
c. Adjustable back stop
d. None of these
ANSWER: A - Number of ampere turns
65) For mesured of overheat ,tempreture sensor embeded with whatstones bridge
principle are use-
Thermal Overload realy
RTD
Induction type
Impedance type
ANSWER : B
Which relay use for reverse phase squence indicate-

Electro magnetic attraction
Induction type
MHO
none of these
ANSWER : B
66) The most efficient torque producing actuating structure for the induction type relays is
a. Shaded pole structure
b. Watt hour meter structure
c. Induction cup structure
d.Single induction loop structure
ANSWER:C- Induction cup structure
67) Saturation flux density of transformers about-

1.7 Tesla
2 Tesla
3Tesla
2.5 Tesla
ANSWER : B
68) Type of Rotor wdg.fault are-
Interturn fault & GND Fault
balance &Unbalance condition
Under voltage & over voltage fault
Over load & over current fault
ANSWER : A
69) An alternator is provided with restricted earth fault protection.the alternator is rated
5000KVA,11000 volt,20% of wdg is to be kept unprotected and relay setting 25%.Find
resistance to be added in neutral to GND connection
20.30
19.36
16.5
18
ANSWER : B
70) In an alternator, the armature reaction will be completely magnetizing in case the load
power factor is-
A.Zero lagging
B.Zero leading
C.0.866
D.Unity
ANSWER : B
71)When the speed of an alternator increases
A.The frequency decrease
B.The frequency increases
C.The frequency remains same
D.The frequency change
ANSWER : B
In huge alternators, the moving part is
A.Brushes
B.Poles
C.Armature
D.None of the above
ANSWER : B
74)The frequency of voltage generated in large alternators is
A.50 Hz
B.60 Hz
C.In kilo cycles
D.In mega cycles
ANSWER : A
75)An alternator coupled to which primemover will usually have the highest rotating speed
A.Steam engine
B.Reciprocating diesel engine

C.Francis turbine
D.Steam turbine
ANSWER : D
76) In an alternator the voltage generated per phase is proportional to
A.Number of turns in coil
B.Flux per pole
C.Frequency of waveform
D.All of the above
ANSWER : D
77)A relatively light loads,transformer efficiency is low because........
A.Second output is lowα
B.Transformer losses are highα
C.Fixed loss is high in proportion to the outputα
D.Cu loss is small
ANSWER : C
78) The no-load current drawn by transformer is usually........
A.0.2% to 0.5%
B. 2% to 5%
C. 2% to 15%
D. 0% to 30%
ANSWER : B
80) Star/star transformers work satisfactorily when........
A.Load is unbalanced onlyα
B.Load is balanced onlyα
C.On balanced as well as unbalanced loadsα
D.None of the above
ANSWER : B
81)Harmonics in transformer result in........
A.Increased core losses
A.Increased I2R losses
C.Magnetic interference with communication circuits
D.All of the above
ANSWER : D
82)Which of the following inductor will have the least eddy current losses?
A. Air core
B. Laminated iron core
C. Iron core
D. Powdered iron core
ANSWER : A
83) The direction of rotation of universal motor can be reversed the by reversing the flow of
current through
A.Armature winding
B.Field winding
C.Either armature winding or field winding
D.None of the above
ANSWER : C
84) The leakage current in the transmission lines is referred to as the
A Resistance
B Radiation
C Conductance
D Polarisation
ANSWER : C
85) Find the receiving impedance of a transmission line having a voltage of 24V and a
conduction current of 1.2A is
A 25.2
B 22.8
C 28.8
D 20
ANSWER : D
86) Find the characteristic impedance expression in terms of the inductance and capacitance
parameters.
A Zo = √(LC)
B Zo = LC
C Zo = √(L/C)
D Zo = L/C
ANSWER : A
87) 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
88) 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 K
ANSWER : C
89) The characteristic impedance of a transmission line depends upon
A shape of the conductor
B surface treatment of the conductors
C conductivity of the material
D geometrical configuration. of the conductors
ANSWER : D
90) When the power is to be transmitted over a distance of 500 km, the transmission voltage
should be in the range
A 150kV - 220Kv
B 110 kV - 150 kV
C 66 kV - 100 kV
D 33 kV - 66 kV
ANSWER : A
91) Neglecting losses in a transmission system, if the voltage is doubled, for the same power
transmission, the weight of conductor material required will be-
A four times
B double
C half
D one fourth
ANSWER : D
92) By which phenomenon does the energy transmission take place between the walls of the
tube in waveguides?
a. Reflection
b. Refraction
c. Dispersion
d. Absorption
ANSWER : A
93) At what pressure is the SF6 gas filled in the whole installation of GIS substations?
a. 3 kg / cm2
b. 5 kg / cm2
c. 3 kg / m2
d. 5 kg / m2
ANSWER : A
94)Three step time distance characteristic of distance relay can be had by
A.Changing taps on voltage transformer
B. Separate measuring elements for zones 2 and 3
C. Switching resistance in relay restrain circuit at pre-set time interval by means of a timer
element
D. Any of the above

ANSWER : D
95) Distance protection scheme is preferred over graded lime-lag over-current protection in
HV and EHV lines because
A. It is faster in operation
B. It is simple
C. It is cheaper in cost
D. All of the above
ANSWER : A
96) A three-step distance protection the reach of the three zones of the relay at the
beginning of the first line typically extends into
A. 100% of the first line, 50% of the second line and 20% of the third line
B. 80% of the first line, of 50% of the second line and 20% of the third line
C. 80% of the first line, 50% of the second line and 10% of the third line
D. 50% of the first line, 50% of the second line and 20% of the third line
ANSWER : B
97) Which of the following relay is/are overload relays?
A. Thermal
B. Electromagnetic
C. Induction
D. All of the above
ANSWER : D
98) Impedance relay may use
A. Balance beam structure
B. Induction cup structure

C. Shaded pole structure
D. Either A or B
ANSWER : D
99) On transient fault OC and impedance relay-
A. Under reaches
B. Over reaches
C. Reach unaffected
ANSWER : A
100) Threshold characteristics of a plain impedance relay in a complex Z plane is a-
A. Circle passing through origin
B. Circle with the centre at the origin
C. Straight line passing through origin
D. Straight line offset from the origin
ANSWER : B
101)Where severe synchronising swing occur, the relay employed is
A. Impedance relay
B. Mho relay
C. Reactance relay
D. Induction relay
ANSWER : B
102) For the protection of lines against faults involving variable fault resistance, the
preferred relaying scheme is a
A. Plain impedance relay

B. Directional over-current relay
C. Mho relay
D. Reactance relay
ANSWER : D
104) Admittance relay
A. Nondirectional relay
B. Directional relay
C. Differential relay
ANSWER : B
105) The relay used for feeder protection is
A. Under voltage relay

B. Translay relay
C. Thermal relay
D. Buchholz relay
ANSWER : B
106) Which one of the following relay has the capability of anticipating the possible
major fault in a transformer ?
A. Over-current relay
B. Differential relay
C. Buchholz relay
D. Over fluxing relay
ANSWER : C
107) Zero sequence current is used for relaying purpose only in the case of
A. Phase over current really
B.Phase impedance relay
C. Ground over current relay
D. Ground impedance relay
ANSWER : C
108) How many relays are used to detect interphase fault of a three line system?
A. One
B. Two
C. Three
D. Six
ANSWER : C
109) For protection of parallel feeders fed from one end, the relays required are-
A. Nondirectional relays at the source end and directional relay at the load end
B. Nondirectional relay at both ends
C. Directional relay at source end and nondirectional relay at load end
D. Directional relay at both ends
ANSWER : A
110) In order that current should flow without causing excessive heating or voltage drop, the
relay contacts should
A. Have low contact resistance
B. Be clean and smooth
C. Be of sufficient size and proper shape
D. Have all above properties
ANSWER : D
Protective Relays page-1
1.A single phasing relay can be used with
a) 1ɸ motor
b) 2r ɸ motor
c) 3 ɸ motor
d) All of these
Ans: (c)
2. A relay is used to
a) Break the fault current
b) Sense the fault
c) Sense the fault and direct to trip the circuit breaker
d) All of these
Ans: (c)
3. In impedance relay, current element torque should be

a) Equal to voltage element torque
b) Greater than voltage element torque
c) Less than voltage element torque
d) None of these
Ans: (a)
4. Over current fault is most likely in

a) Transformer
b) Overhead line equipment
c) Alternator
d) Motors
Ans: (b)
5. Plug setting of a relay can be changed by changing

a) Air gap
b) Back up stop
c) Number of ampere turns
d) All of these
Ans: (c)
6. Distance relays are generally

a) Impedance type
b) MHO type
c) Reactance type
d) All of these
Ans: (b)
7. Buchholz relay is used to protect against

a) Inter-turn fault
b) External faults
c) Rotor faults
d) Every internal faults
Ans: (d)
8. Instantaneous relay should operate within
a) 0.0001 sec
b) 0.001 sec
c) 0.01 sec
d) 0.1 sec
Ans: (c)
9. MHO relay is inherently a

a) Direconal type
b) Non-direconal type
c) Unidireconal type
d) None of these
Ans: (a)
10. Basic relay connection requirement is that the relay must operate for
a) Load
b) Internal faults
c) Both (a) and (b)
d) None of these
Ans: (b)
11. An impedance relay is used for

a) Earth faults
b) Interphase faults
c) Both (a) and (b)
d) None of these
Ans: (c)
12. Relay gets its operating energy from

a) Transformer
b) Alternator
c) Overhead lines
d) C.T., P.T.
Ans: (d)
13. Good relay should possess

a) Speed & reliability
b) Aped & sensivity
c) Adequateness & selecvity
d) All of these
Ans: (d)
14. Earthing transformer is used to

a) Improve neutral wire’s current capacity
b) Avoid overheang of transformer
c) Provide arficial earthing
d) Avoid harmonics
Ans: (c)
15. Percentage differential protection is used to prevent against

a) Inter-turn faults
b) Heavy Loads
c) External Faults
d) Magnezing current
Ans: (d)
16. Back up protection is needed for

a) Over voltage
b) Short circuits
c) Over current
d) All of these
Ans: (b)
17. An instantaneous relay is

a) Permanent moving magnet
b) Inducon cup
c) Shaded pole
d) Moving coil
Ans: (a)
18. Relays for transmission line protection are

a) In three zones
b) In two zones
c) Independent of zone
d) None of these
Ans: (a)
19. Induction cup relays responds to

a) Current
b) Power
c) Voltage
d) Impedance
Ans: (d)
20. Split-phase relay responds to

a) Over load faults
b) Over voltage
c) Inter turn faults
d) All of these
Ans: (c)
21. Time classification of relays includes

a) Instantaneous relays
b) Definite me lag
c) Inverse me lag
d) All of these
Ans: (d)
22. Directional relays responds to

a) Power
b) Voltage
c) Current
d) Reactance
Ans: (a)
23. Single phase preventers are used for

a) Transmission lines
b) Transformers
c) Motors
d) Underground cables
Ans: (c)
24. In carrier current protection, wave trap is used is for trapping

a) High frequency waves entering in generang units
b) Power frequency waves
c) Both (a) and (b)
d) None of these
Ans: (a)
25. Operating current in relay is

a) A.c. only
b) D.c. only
c) Both (a) and (b)
d) None of these
Ans: (c)
26. For phase fault on long line, which relay is used?

a) MHO relays
b) Reactance relays
c) Impedance relays
d) All of these
Ans: (c)
27. For motor protection, which relay is used?

a) Thermocouple type relays
b) Bimetallic relays
c) Electronic relays
d) All of these
Ans: (d)
28. For protection against synchronizing power surges, which relay is used?
a) Split-phase relays
b) Impedance relays
c) Reactance relays
d) MHO relays
Ans: (d)
29. Pilot wire protection is for

a) Overhead lines
b) Transformer
c) Motors
d) Cables
Ans: (a)
30. Under voltage relays are used for

a) Motors
b) Alternators
c) Bus bars
d) All of these
Ans: (d)
31. In an impedance relay, fault current is maximum if fault occurs near the
a) Relay
b) Center of the line
c) Transformer
d) None of these
Ans: (a)
32. More faults occur in

a) Generators
b) Under ground cables
c) Transformers
d) Over head lines
Ans: (d)
33. Actual tripping of a static relay is obtained by

a) SCR
b) Thyristors
c) UJT
d) None of these
Ans: (d)
34. Instantaneous relay is

a) Hinged armature type
b) Polarized type
c) Balanced beam type
d) All of these
Ans: (a)
35. It is possible to work on ungrounded systems of 11 kV for a length of

a) 10 Kms
b) 50 Kms
c) 90 kms
d) 110 Kms
Ans: (d)
36. Advantage of grounded neutral is

a) Persistent arcing grounds are eliminated
b) Earth fault are ulized to disconnect the fault
c) Both (a) and (b)
d) None of these
Ans: (c)
37. Neutral can be grounded by

a) Solid grounding
b) Resistance grounding
c) Reactance grounding
d) All of these
Ans: (d)
38. Thyrite is used in lightning arrestors because of its

a) Straight line characterisc
b) Non-linear characterisc
c) None of these
d) All of these
Ans: (b)
39. Location of lightning arrestor is

a) Aer the transformer
b) Aer the distributor
c) Before the transformer
d) None of these
Ans: (c)
40. Lightning arrestors are

a) Surge reflectors
b) Surge divertors
c) Surge absorbers
d) Surge aenuators
Ans: (b)
41. Relays for transmission line protection are

a) In three zones
b) In two zones
d) None of these
Ans: (a)
1. Plug setting of a relay can be
altered by varying .
a)Air gap of magnetic path

b) Number of ampere-turns
c) Adjustable back up stop

d) None of
these Ans:
2. If the operation of a relay does not involve any change in air gap, then the
ratio of rest to pick up is usually .
a) Low
b) Medium
c) High
d) Independent of the change in
air gap Ans:
3. Drop out to cutoff ratio for most relays is of the order of .
a) 0.2 to 0.3
b) 0.3 to 0.4
c)
0
.
4
t
o
0
.
6
d
)
0
.
t
o
1
.
Ans:
4. Basic quantity measured in a distance relay is .
a) Impedance
b) Current difference
c) Voltage difference
d) None of
these Ans:
5. Which of following are the desirable qualities of protective relays?
a) Stability, reliability
b) Speed sensitivity
c) Selectivity,
adequacy d) No ne
o f t hese
Ans:
6. Protective relays are devices which detect abnormal conditions in
electrical circuit by measuring .
a) Current during abnormal condition

b) Voltage during abnormal condition
c) Both (a) and (b) simultaneously
d) Co nst ant ly t he e lect r ica l qua nt it ie s whic h d iffer dur ing no r ma l
a nd a bno r ma l co nd it io ns Ans:
7. Time interval from instant of contact separation to time of arc extinction is

called .
a) Arcing time
b) Opening time
c) Closing time
d) None of
these Ans:
8. A distance relay measures .
a) Current difference
b) Voltage difference
c) Impedance difference
d) Distance between two
CT’s Ans:
9. Maximum short circuit current occurs due to .
a) Line-to-line fault
b) Line-to-line circuit
c) Dead short circuit
d) Bot h ( a) and ( b) o ccur r ing s imu
lt a neo us ly Ans:
10. Buchholz relays are used for transformers of ratings above .
a) 100 kV
b) 200 kV
c) 500 kV
d) 1000
kV Ans:
11. The voltage appearing across the contacts after the opening of the
circuit breaker is called .
a) Arc voltage
b) Recovery voltage
c) Surge voltage
d) Break open
voltage Ans:
12. Air blast circuit breaker is operated at a pressure of .
a) 5 to 10 kg/cm2
2
b) 10 to 15 kg/cm
2
c) 15 to 20 kg/cm
d) 20 to 30
kg/cm2 Ans:
13. The basic problem in a circuit breaker is to .
a) Maintain the arc

b) Emit ionization electrons
c) Extinguish the arc
d) None of
these Ans:
14. In oil and air blast circuit breakers, the current zero interruption is attained
by .
a) Lengthening of arc
b) Cooling and blast effect
c) Deionizing the oil with
forced air d) Bot h ( a) and (
b) abo ve
Ans:
15. Buchholz relay is used for the protection of .
a) Alternators
b) Transformers
c) Switch yard
d) Transmission
lines Ans:
16. Which of the following is a directional relay?
a) Reactance relay
b) Mho relay
c) Reactance
relay d) Bot h (
b) and ( c)
Ans:
17. Which of the following is an instantaneous relay?
a) Induction type
b) Shaded pole type
c) Thermocouple type
d) Per ma ne nt mag net mo ving
co il t ype Ans:
18. Which of the following is not an instantaneous relay?
a) Polarized type
b) Balance beam type
c) Hinged armature
type d) I nduct io n
d isc t ype
Ans:
19. Directional relays respond to the .
a) Voltage polarities
b) Flow of current
c) Flow of power
d) All of
these Ans:
20. In a circuit breaker, are

is initiated by the process of .
a) Thermal emission
b) Alternators
c) Field emission
d) Tr ans mis s io n
line s Ans:
21. Bulk oil circuit breaker is suitable for voltages up to .
a) 4 kV
b) 25 kV
c) 10
kV d)
36 kV
Ans:
22. Circuit breakers are essentially .
a) Current carrying contacts called electrodes

b) Arc extinguishers
c) Transformers to isolate two systems
d) Circuits to break the
system Ans:
23. The voltage across the circuit breaker pole after final current zero is.
b) Supply voltage
c) Recovery voltage
d) None of
these Ans:
24. Which of the following circuit breakers takes minimum time installation?
a) Bulk oil circuit breaker

b) Minimum oil circuit breaker
c) Air blast circuit
breaker d) SF6 c ir cu
it br eaker
Ans:
25. In a power system, the rate of rise of Restriking voltage depends upon .
a) Circuit power factor only

b) Switching condition only
c) Both (a) and (b) above
d) None of
these Ans:
26. In a circuit breaker, the arcing contents are made of .
a) Aluminum
b) Electrolytic
c) Copper tungsten alloy
d) Tungst
en Ans:
27. The following medium is employed for extinction of arc in air break circuit
breakers?
a) Air
b) Oil
c) Water
d) None of
these Ans:
28. The following circuit breaker does not use pneumatic operating mechanism
.
a) Air brake circuit breaker

b) Air blast circuit breaker
c) Bulk oil circuit breaker
d) SF6 circuit
breaker Ans:
29. In a circuit breaker, are is initiated by the process of .
a) Thermal emission
b) Alternators
c) Field emission
d) Tr ans mis s io
n line s Ans:
30. Bulk oil circuit breaker is suitable for voltages up to .
a) 4 kV
b) 25 kV
c) 10
kV d)
36 kV
Ans:
31. Circuit breakers are essentially .
a) Current carrying contacts called electrodes
b) Arc extinguishers
c) Transformers to isolate two systems
d) Circuits to break the
system Ans:
32. The voltage across the circuit breaker pole after final current zero is.
b) Supply voltage
c) Recovery voltage
d) None of
these Ans:
33. Which of the following circuit breakers takes minimum time installation?
a) Bulk oil circuit breaker

b) Minimum oil circuit breaker
c) Air blast circuit
breaker d) SF6 c ir cu
it br eaker
Ans:
34. In a power system, the rate of rise of Restriking voltage depends upon .
a) Circuit power factor only

b) Switching condition only
c) Both (a) and (b) above
d) None of
these Ans:
35. In a circuit breaker, the arcing contents are made of .
a) Aluminum
b) Electrolytic
c) Copper tungsten alloy
d) Tungst
en Ans:
36. Fault diverters are basically .
a) Circuit breakers
b) Fast switches
c) Relays
d) Fuse
s Ans:
37. The following medium is employed for extinction of arc in air break circuit
breakers?
a) Air
b) Oil
c) Water
d) None of
these Ans:
38. The following circuit breaker does not use pneumatic operating mechanism
.
a) Air brake circuit breaker

b) Air blast circuit breaker
c) Bulk oil circuit breaker
d) SF6 circuit
breaker Ans:
39. Time classification of relays

includes .
a) Instantaneous relays
b) Definite time lag
c) Inverse time
lag d) All o f t
hes e
Ans:
40. Directional relays responds to .

a) Power
b) Voltage
c) Current
d) Reactan
ce Ans:
41. In carrier current protection, wave trap is used is for trapping .
a) High frequency waves entering in generating units
b) Power frequency waves

c) Both (a) and (b)
d) None of
these Ans:
42. Operating current in relay is .
a) A.C. only
b) D.C. only
c) Both (a) and (b)
d) None of
these Ans:
43. For phase fault on long line, which relay is used?
a) MHO relays
b) Reactance relays
c) Impedance relays
d) All of
these Ans:
44. For motor protection, which relay is used?
a) Thermocouple type relays

b) Bimetallic relays
c) Electronic
relays d) All o f
t hes e
Ans:
45. Pilot wire protection is for .
a) Overhead lines
b) Transformer
c) Motors
d) Cable
s Ans:
46. Under voltage relays are used for .
a) Motors
b) Alternators
c) Bus bars
d) All o f t
hes e Ans
47. An impedance relay is used for .
a) Earth faults
b) Interphase faults
c) Both (a) and (b)
d) None of
these Ans:
48. Relay gets its operating energy from .
a) Transformer
b) Alternator
c) Overhead
lines d) C. T. ,
P. T.
Ans:
49. Good relay should possess .
a) Speed & reliability

b) Aped & sensitivity
c) Adequateness &
selectivity d) All o f t hes
e
Ans:
50. Percentage differential protection is used to prevent against .
a) Inter-turn faults
b) Heavy Loads
c) External Faults
d) Magnet iz ing
cur r ent Ans:

51. Back up protection is needed for .
a) Over voltage
b) Short circuits
c) Over current
d) All of
these Ans:
52. An instantaneous relay is .
a) Permanent moving magnet

b) Induction cup
c) Shaded pole
d) Moving
coil Ans:
53. Relays for transmission line protection are .
a) In three zones
b) In two zones
d) None of
these Ans:
54. Induction cup relays responds to .
a) Current
b) Power
c) Voltage
d) I mpeda
nce Ans:
55. Split-phase relay responds to .
a) Over load faults

b) Over voltage
c) Inter turn faults
d) All of
these Ans:
56. A relay is used to .
a) Break the fault current

b) Sense the fault
c) Sense the fault and direct to trip the circuit breaker
d) All of
these Ans:
57. In impedance relay, current element torque should be .
a) Equal to voltage element torque

b) Greater than voltage element torque
c) Less than voltage element torque
d) None of
these Ans:
58. Over current fault is most likely in .
a) Transformer
b) Overhead line equipment
c) Alternator
d) Moto
rs Ans:
59. Plug setting of a relay can be changed by changing .
a) Air gap
b) Back up stop
c) Number of ampere turns
d) All of
these Ans:
60. Distance relays are generally .
a) Impedance type
b) MHO type
c) Reactance type
d) All of
these Ans:
61. Buchholz relay is used to protect against .
a) Inter-turn fault
b) External faults
c) Rotor faults
d) E ver y int er na l
fau lt Ans:
62. Instantaneous relay should operate within .
a) 0.0001 sec
b) 0.001 sec
c) 0.01 sec
d) 0.1
sec
Ans:
63. MHO relay is inherently a .
a) Directional type
b) Non-directional type
c) Unidirectional type
d) None of
these Ans:
64. Basic relay connection requirement is that the relay must operate for .
a) Load
b) Internal faults
c) Both (a) and (b)
d) None of
these Ans:
65. In an impedance relay, fault current is maximum if fault occurs near the .
a)Re la y
b) Center of the line
c) Transformer
d) None of
these Ans:
66. More faults occur in .
a) Generators
b) Underground cables
c) Transformers
d) Over head -
line s Ans:
67. Actual tripping of a static relay is obtained by_ .
a) SCR
b) Thyristors
c) UJT
d) No ne o f t
hese Ans:
68. Instantaneous relay is .
a) Hinged armature type
b) Polarized type
c) Balanced beam type
d) All of
these Ans:
69. Relays for transmission line protection are .
a) In three zones
b) In two zones
d) None of
these Ans:
70. Plug setting of a relay can be altered by varying .
a) Air gap of magnetic path

b) Number of ampere-turns
c) Adjustable back up stop

d) None of
these Ans:
71. Drop out to cutoff ratio for most relays is of the order of .
a) 0.2 to 0.3
b) 0.3 to 0.4
c) 0.4 to 0.6
d) 0. 6 to
1. 0
Ans:
72. Basic quantity measured in a distance relay is_ .
a) Impedance
b) Current difference
c) Voltage difference
d) None of
these Ans:
73. Which of following are the desirable qualities of protective relays?
a) Stability, reliability
b) Speed sensitivity
c) Selectivity,
adequacy d) No ne
o f t hese
Ans:
74. Protective relays are devices which detect abnormal conditions in

electrical circuit by measuring .
a) Current during abnormal condition

b) Voltage during abnormal condition
c) Both (a) and (b) simultaneously
d) Co nst ant ly t he e lect r ica l qua nt it ie s whic h d iffer dur ing no r ma l
a nd a bno r ma l co nd it io ns Ans:
75. Time interval from instant of contact separation to time of arc extinction is
called .
a) Arcing time
b) Opening time
c) Closing time
d) None of
these Ans:
76. A distance relay measures .
a) Current difference
b) Voltage difference
c) Impedance difference
d) Distance between two
CT’s Ans:
77. Maximum short circuit current occurs due to .
a) Line-to-line fault
b) Line-to-line circuit
c) Dead short circuit
d) Bot h ( a) and ( b) o ccur r ing s imu
lt a neo us ly Ans:
78. Fusing factor should be .
a) Equal to zero
b) Less than now
c) Equal to
one d) Mor e
t han o ne
Ans:
79. Fuse wire should possess .
a) High specific resistance and high melting point

b) High specific resistance and low melting point
c) Low specific resistance and low melting
point d) Lo w spec if ic r es ist ance a nd
hig h me lt ing po int
Ans:
80. If strands are twisted, then fusing current will_ .

a) Increase
b) Reduce
c) Remain same
d) May increase or
decrease Ans:
81. Fusing factor is defined as the ratio between .
a) Maximum fusing current and rated voltage

b) Maximum fusing current and rated
current c) M inimu m fu s ing cur r
ent and r at ed cur r ent
d) Minimum fusing current and rated
voltage Ans
82. Fuses can serve up to a current of .
a) 25 A
b) 50 A
c) 75 A
d) 100
A
Ans:
83. Cut-off current in a fuse is the .
a) Maximu m va lue act ua lly r eac
hed
b) R.m.s. value actually reached
c) Average value actually reached
d) None of
these Ans:
84. H.R.C. fuse have .
a) High rating of current

b) H ig h r upt ur ing capac it y
c) High resistance capacity
d) None of
these Ans
85. Cartridge type fuse can be used up to a voltage of .
a) 400 V
b) 11 kV
c) 20
kV d)
33 kV
Ans:
86. Liquid type H.R.C. fuses are used up to a voltage of .
a) 33 kV
b) 66 kV
c) 132
kV
d) 200 kV
Ans:
87. Ionization in circuit breakers is facilitated by .
a) Increase of field strength

b) Increase of mean free path
c) High
temperature d)
All o f t hes e
Ans:
88. Arc interruption is done by .
a) High resistance interruption

b) Low resistance
interruption c) Bot h ( a)
and ( b)
d)
o
f
89. Part of circuit breaker helpful in breaking the current is .
a) Trip Coil
b) Contacts
c) Handle
d) Mediu
m Ans:
90. Desired tripping of a circuit breaker is _.
a) Manually
b) Aut o mat ic a lly
c) That it should give warning
d) None of
these Ans:
91. Arcing time is the time between .
a) Separ at io n o f c ir cu it br eaker and e xt inct io n o f a r c

b) Separation of circuit breaker and rise of recovery voltage
c) Normal current interruption and arc extinction
d) None of
these Ans:
92. For single frequency transients, ratio of peak Restriking voltage to time
between voltage
zero and peak voltage is called .
b) Recovery voltage
c) Rat e o f r ise Rest r ik ing vo lt age
d) Active recovery
voltage Ans:
93. Time between energization of trip coil and separation of contacts is called
.
a) Closing time
b) Opening time
c) Both (a) and
(b) d) No ne o f
t hese
Ans:
94. In circuit breaker, to facilitate arc quenching, dielectric strength can

be increased by .
a) Lengthening of the gap

b) Cooling
c) Blast
effect d) All
o f t hes e
Ans:
95. Rate of rise Restriking voltage depends upon_ .
a) Active recovery voltage

b) Natural frequency of
oscillations c) Bot h ( a) and (
b)
d) Rating of circuit
breaker Ans:
96. An ideal circuit breaker should offer .
a) Zer o & inf in it e imped a nce be fo r e & a ft er int er rupt io n r espect ive ly
b) Infinity & zero impedance before & after interruption respectively
c) Equal impedance before & after interruption
d) None of
these Ans:
97. Interrupting a low inductive current may lead to .
a) Very high Restriking voltage

b) Very high current
c) Rupture of circuit
breaker d) Cur r ent
cho pping
Ans:
98. Instantaneous voltage in a circuit breaker depends upon .
b) Rate of rise Restriking
voltage c) Po wer facto r
d)
F
r
e
q
u
e
n
c
y
A
n
s
:
99. Current chopping can be avoided by .
a) Resistance switching
b) Inductive switching
c) Capacitive switching
d) Diode
switching Ans:
100. Recovery voltage is the value of the r.m.s. voltage that re-appears across
the poles of a circuit breaker before .
b) Fina l ar c d ist inct io n
c) Rise of voltage
d) All of
these Ans:
101. A.C. air brake circuit breakers are used for .
a) Very high voltage

b) Very low voltage
c) Medium voltage
d) Med iu m a nd lo
w vo lt age Ans:
102. Quantity of oil in bulk oil circuit breakers increases with .
a) Decrease in voltage
b) Increase in voltage
c) Pressure of arc
d) Mechanical
stresses Ans:
103. Air blast circuit breakers are preferred for .
a) Short duty
b) Intermittent duty
c) Repeated duty
d) All of
these Ans:
104. Rating of circuit breaker depends upon .
a) Breaking capacity
b) Making capacity
c) Short time
capacity d) All o f
t hes e
Ans:
105. Phenomenon of arc interruption takes place at .
a) Zero voltage
b) Zero current
c) High current
d) High voltage
Ans:
106. Symmetrical breaking current is .
a) Peak value of A.C. component

b) Average value of A.C. component
c) R.m.s. value of A.C. component
d) All of
these Ans:
107. In vacuum breakers, current wave _.
a) Reaches its maximum value

b) Attains its r.m.s. value
c) Is chopped
d) Attains its average
value Ans:
108. In oil circuit breakers, dielectric strength of oil should be .
a) High
b) Low
c) Medium
d) None of
these Ans:
109. Main disadvantage (s) of oil circuit breaker is that it .
a) Is easily inflammable
b) May from an explosive mixture with air
c) Requires
maintenance d) All
o f t hes e
Ans:
110.. Breaker should adjust itself to .

a) Fault magnitude and time
b) Increased arc and time of quenching

c) R R R V
d) None of
these Ans:
111. Curr
ent copping tendency is minimized by using the F6 gas at
relatively .
a) High pressure and low velocity.

b) High pressure and high velocity.
c) Low pressure and low velocity.
d) Low pressure and high
velocity. Ans:
112. Mho relay is normally used for the protection of .
a) Lo ng t r ans mis s io n line s.

b) Medium length lines.
c) Short length lines.
d) No length
criterion. Ans
113. Resistance switching is normally resorted in case of .
a) Bulk oil circuit breakers.

b) Minimum oil circuit
breakers. c) Air blast c ir cu
it br eaker s.
d) All
type
s of
brea
kers.
Ans:
114. Stability of arc in vacuum depends upon .
a) The contact material only.

b) The contact material and its vapor pressure.
c) The circuit parameters only.
d) T he co mbinat io n o f (
b) and ( c) . Ans:
115. Chances of arc interruption in subsequent current zeros .
a) Increases in case of ABCD but decreases in OCB.

b) Decreases in case of ABCD but decreases in OCB.
c) Decreases in both the cases.
d) Increases in both the
cases. Ans:
116. A 3-phase breaker is rated at 2000 MVA, 33kV, its making current will be .
a) 35 kA
b) 49 kA
c) 70
kA d)
89 kA
Ans:
117. Carrier current protection scheme is normally used for .
a) HV transmission lines only.

b) HV cables only.
c) HV transmission and cables.
d) None of the
above. Ans:
118. Where voltages are high and current to be interrupted is low the
breaker preferred
is .
a) Air blast C.B.

b) Oil C.B.
c)Vacuu m C. B.
d) Any one of the
above. Ans:
119. If the time of operating of a relay for unity TMS is 10secs., the time of
operation for 0.5 TMS will be .
a) 20 secs.
b) 5 secs.
c) 10 secs.
d) None of the
above Ans:
120. Phase comparators in case of static relays and electro-mechanical

relays normally
are.
a) Sine and cosine comparators respectively
b) Co s ine a nd s ine co mpar at o r s r espect ive ly.
c) Both are cosine comparators.
d) Both are sing comparators.
Ans:
121. Buchholz relay is used for .
a) Carrier protection.
b) Tr ans fo r mer pr ot ect io n.
c) Generator protection.
d) Motor
protection. Ans:
122. The relay with inverse time characteristics will operate within .
a) 10 ms
b) 5 to 10s
c) 10 to 20s
d) above
25 s Ans:
123. IDMT relays are used to protect the power transformer against .
a) External short circuit

b) Overloads
c) Internal short
circuits d) Bot h a &
b
Ans:
124. In case of electro mechanical relay, relay coil is normally designed for
. a) 1 & 5 A
b) 5 and 10 A
c) 10 and 25A
d) 50 and100
A Ans:
125. If the time of operation of a relay for unity TMS is 10 sec, the time of
operation for 0.4
TMS will be .
a) 4s
b) 25 s
c) 10 s
d) none of
these. Ans:
126. An over-current relay, having a current setting of 125% is connected to a

supply circuit
through a current transformer of ratio 400/5. The pick-up value is .
a) 6. 25 A
b) 10 A c)
12.5 A
d
127. In an inverse definite minimum time electromagnetic type over

current relay, the
minimum time feature is achieved because of .
a) Saturation of the magnetic circuit.

b) Proper mechanical design.
c) Appropriate time delay element
d) Electromagnetic
damping. Ans:
128. Which of the following is/are distance relays?
a) Impedance
b) Reactance,
c) Mho.
d) All o f t he
abo ve Ans:
129. Impedance relay may use .
a) Balance beam structure

b) Induction cup structure
c) Shaded pole
structure d) E it her
AorB
Ans:
130. Threshold characteristics of a plain impedance relay in a complex Z plane is
a .
a) circle passing through origin.

b) C ir c le w it h ce nt er at t he o r ig in
c) Straight line passing through origin
d) Straight line offset from the
origin Ans:
131. Admittance relay is .
a) Non-directional relay.
b) Directional relay.
c) Differential relay.
d) None of
these. Ans:
132. MHO relays have an RX plane characteristic depicted by .
a) A straight line passing through origin

b) A straight line parallel to X axis
c) A straight line parallel to R
axis d) A c ir c le pas s ing t
hr o ugh o r ig in
Ans:
133. The relay best suited for phase fault relaying for medium
transmission line
is .
a) MHO relay.
b) Reactance relay.
c)I mpeda nc e r e la y. d) None of
these. Ans:
134. For ground fault, we prefer .
a) Plain impedance relay

b) Directional
relay. c) React
ance r e la y.
d) Over-current relay.
Ans:
135. For the protection of lines against faults involving variable fault
resistance, the preferred relaying scheme is .
a) Plain impedance relay.

b) Directional over-current relay.
c) MHO relay.
d) React ance
r e la y. Ans:
136. The relay used for phase fault protection of short transmission lines is .
a) Reactance relay
b) Impedance relay.
c) MHO relay
d) IDMT
relay Ans:
137. The relay best suited for phase fault relaying for long transmission lines is
.
a) MHO r ela y.
b) Reactance relay.
c) Impedance relay.
d) Induction
relay. Ans:
138. Where severe synchronizing swing occurs, the relay employed is .
a) Impedance relay.
b) MHO r e la y.
c) Reactance relay.
d) Induction
relay. Ans:
139. Which of the following relays has inherent directional characteristic?
a) MHO.
b) Reactance.
c) Impedance.
d) None of the
above. Ans:
140. For the protection of a very long extra high voltage line, the protective
relay used
is .
a) Over current with extremely inverse characteristics.

b) Percentage differential relay.
c) Reactance type distance
relay d) MHO t ype d ist
anc e r e la y.
Ans:
141. A relay used for protection of motors against overload is .
a) Induction relay.
b) T her ma l r e la y.
c) Impedance relay.
d) MHO
relay. Ans:
142. A differential relay responds to .
a) Algebraic difference of two or more similar electrical

quantities.
b) Phasor difference of two or more similar electrical quantities.
c) Algebraic difference between two currents.
d) Algebraic difference between two
voltages. Ans:
143. Differential relays are used for protection of_ .
a) Feeders.
b) Alternators
c) Transforme
rs. d) All o f t
hese.
Ans:
144. Both voltage and current signals are required for .
a) A plain over-current relay.

b) A differential relay.
c) A directional relay.
d) A biased differential
relay. Ans:
145. The relay used for feeder protection is .
a) Under-voltage relay.
b) Translay relay.
c) Thermal relay.
d) Buchholz
relay. Ans:
146. In the case of transmission line protection, over current relay is used .
a) Only up to 110 kV.

b) Only up to 220 kV.
c) Only up to 50 kV.
d) Only up to
1,100kV Ans:
147. The protection from negative sequence current is provided for .
a) Transformer
b) Transmission line
c) Motors
d) Gener
ato r s Ans:
148. A relay which has no moving parts and performs measurement with solid
state circuit
is .
a) Differential relay
b) Static relay
c) Induction type relay
d) Thermal
relay Ans:
149. Which of the following relay does not make use of electromagnetic force
.
a) Attracted armature type relay

b) Solenoid & plunger type
impedance relay c) St at ic r e la y
d)
Indu
ctio
type
rela
Ans:
150. Over conventional electromechanical relays, the transistor relay has the
limitations of
.
a) Characteristics varying with temperature and aging

b) Low short time overload capacity
c) Reliability dependent upon the large no of small components and
their elect. conn. d) All o f t he abo ve
Ans:
151. In a static overload relay, inverse time characteristics are obtained by.
a) A transistor amplifier
b) An int egr at ing c ir cu it
c) A transistor switch.
d) A differentiating
circuit Ans:
152. A static coincidence circuit is used for .
a) Phase comparison
b) Amplitude comparison
c) Starting an impedance relay
d) Biasing a MHO
relay Ans:
153. Two input phase comparator in a static relay is made up of a .
a) Transformer amplifier
b) Transistor logic
circuit c) Rect ifier br
idge
d) Thyristor Bridge
Ans:
154. As compared to electromagnetic relays, static relays are .
a) Less suitable for auto reclosing

b) More suitable for auto reclosing
c) Both
d) None of
these Ans:
155. The phase comparators in case of a static relays and electromechanical

relays normally are .
a) Cosine and Sine comparators respectively

b) Sine & Cosine comparators respectively
c) Both are sine comparators
d) Both are cosine
comparators Ans:
156. Merz price protection is a type of .
a) Distance protection
b) D iffer e nt ia l pr ot ect io n
c) Both (a) & (b)
d) Neither (a) nor
(b) Ans:
157. Merz Price protection is employed for protection of .
a) alternators.
b) transformers.
c) transmission
lines. d) bot h ( a)
and ( b).
Ans:
158. Merz-Price relays are used for .
a) motor protection,
b) capacitor protection.
c) rectifier
protection. d)
gener ato r prot ect
io n.
Ans:
159. The boundary of a protective system is determined by the location of .
a) circuit breakers.
b) transforme
rs. c) CTs.
d)
160. Differential protection scheme is used for alternators of capacity more than .
a) 500 kVA.
b) 1 MVA.
c) 2 MVA.
d) 25
MVA.
Ans:
161. Flow of unbalanced three-phase currents through the stator winding of an

alternator will
cause .
a) Vibration of the rotor.

b) Heat ing o f t he roto r.
c)
Decelerati
on of the
rotor. Ans:
162. The short-circuit current of an alternator, in case of line to line fault,

depends on its .
a) Short-circuit resistance.
b) Transient reactance.
c)Sync hr o no us r eact ance
d) None of the
above Ans:
163. We do not require any protection against prime mover failure in case of .
a)Tur bo- gener at or set s.

b) Hydro-generator sets.
c) Diesel-engine driven alternators.
d) Back pressure turbo-
generators. Ans:
164. The most common type of protection used or stator winding faults such as
phase to phase
or phase-to- ground short circuit in case of alternator is .
a) Over-current protection.
b) Mer z- Pr ice pr ot ect io n.
c) Buchholz protection.
d) None of the
above. Ans:
165. A large-size generator is protected against overloads by providing .
a) Thermal relays.
b) Over-current relays.
c)T her ma l se ns it ive r e la ys.
d) Either of the
above Ans:
166. For the protection of stator winding of an alternator against internal

fault involving
ground, the relay used is .
a) Biased differential relay.
b) Dover-current relay.
c) Plain impedance relay.
d) Buchholz
relay. Ans:
167. The bias factor S in unit protection synchronous generators .
a)L ies bet ween 0. 05 and 0. 1 pu.

b) Is less than 0.05 pu
c) Lies between 0.10 to 0,25 pu
d) Is greater than 0.25 pu
Ans:
168. As soon as a fault develops in a generator stator, it is essential to

suppress field excitation, otherwise .
a) Terminal voltage will drop.

b) It may lead to loss of synchronism.
c)It will co nt inue to supply po wer to t he st ato r wind ing fau lt .
d) all of the
above. Ans:
169. For the protection of a large squirrel cage induction motor against
single phasing normally .
a) An over-current relay is used.

b) A differential relay is used.
c) A directional relay is used,
d) Negat ive- seque nce cur r e nt sens it
ive r e la y is use d, Ans:
170. The main function of under voltage protective device generally employed
with a motor starter is to .
a) Open the supply circuit on failure of power supply
b) Control the motor voltage.

c) Prevent the opening of supply circuit
d) None of the
above. Ans:
171. The types of faults that occur in electric motors are .
a) Stator.
b) Rotor.
c) Over-load.
d) Under-voltage.
e) Unbalanced supply voltages and reverse or open
phase starting. f) All o f t he abo ve.
Ans:
172. Earth fault protection for an electric motor is provided by means of .
a) Instantaneous over-current relay.

b) Instantaneous relay having a setting of approximately 30% of motor rated
current in the residual circuits of two CTs.
c) Ground
wire d) Bot
hb&c
Ans:
173. The relay used for protection of power transformers against internal faults
is .
a) Buchho lz r e la y
b) MHO relay
c) Induction relay
d) Impedance
relay Ans:
174. In Merz price percentage differential protection of a Δ- Y

transformer, the CT
secondary’s connection in the primary & secondary winding of the transformer
would be in the form of .
a) Δ- Y
b) Y- Δ
c) Δ- Δ
d) Y-Y
Ans:
175. For differential protection of power transformer (Δ- Δ) the current

transformer will
have .
a) Δ- Δ connection
b) Y- Δ
connection c)
Y- Y co nnect io
n
d) Δ
–Y
co
nn
ec
ti
ns
:
176. A 3 –phase 11/66 kV delta / star transformer protected by Merz price
scheme has CT ratio
of 400/5 on LT side. Ratio of CT on HT side will be equal to .
a)
b)1:23:1
23
c) 23: √3
d) √3:23
Ans:
177. To prevent maloperation of differentially connected relay while energizing

a transformer
the relay restraining coil is biased with _.
a) Seco nd har mo nic cur r ent

b) Third harmonic current
c) Fifth harmonic current
d) Seventh harmonic
current Ans:
178. The percentage differential protection of a transformer protects the

transformer against
.
a) External faults
b) Magnetizing current inrush
c) Overloadin
g d) I nt er
na l fau lt
Ans:
179. Magnetizing inrush current in a transformer in rich is .
a) Third harmonic component

b) Fifth harmonic component
c) Second harmonic component
d) All odd harmonic
component Ans:
180. Magnetizing inrush phenomena occur in .
a) Large t r ans fo r mer pr imar y o nly, w he n t he tr ans f o r mer is sw it c

hed o n
b) Large transformer primary when a three-phase fault occurs in the
secondary
c) Large transformer secondary when the transformer is switched on in the
Primary
d) None of the
above. Ans:
181. For the protection of transformer harmonic restraint is used to guard

against .
a) Magnet iz ing inr us h cur r e nt

b) Unbalanced operation
c) Lightening
d) Switching over
voltage Ans:
182. The connections of CT’s are opposite to that of transformer windings so

that current in
the pilot wires of two are / have .
a) Same p ha se
b) Opposite in phase
c) Phase difference of 60 degrees
d) Phase difference of 90
degrees Ans:
183. For preventing the maloperation of Merz price protection scheme on inrush
of
magnetizing current .
a) T he r ela y r est r a ining co il is biased w it h t he seco nd har mo nic cur r

ent .
b) Time lag is provided in the relay.
c) Relay sensitivity is reduced by employing shunt.
d) All of the
above. Ans:
184. Problems associated with differential protection is / are
a) Magnetizing in-rush current.

b) Mismatching characteristics of CTs.
c) Change of ratio as a result of
tapping. d) Oil a ll o f t he abo ve
.
Ans:
185. protection used for protection of transmission line is a unit type
protectio
n.
a) Distance
b) Current graded over-current
c) Carrier current
d) Time graded over-
current Ans:
186. A transmission line is protected by

_.
a) Distance protection.
b) Current graded over-current protection.
c) Time graded over-current protection.
d) In-rush
protection. e) ( a),
( b) and ( c) .
Ans:
187. Graded time lag over-current relaying without directional features can he
employed for
protection of .
a) Ring mains.
b) Parallel feeders.
c) Radial feeders.
d) None of the
above Ans:
188. Time graded protection of a radial feeder can be achieved by using .
a) Definite time relays.

b) Inverse time relays.
c)Bot h defin it e and inver se t ime r e la ys,
d) None of the
above. Ans:
189. For the protection of parallel feeders fed from one end the relays required
are .
a) Non-directional relays at the source end and directional relays at the load
end.
b) Non-directional relays at both the ends.

c) Direction relays at the source end and non-directional relays at the load
end.
d) Directional relays at both the ends.
Ans:
190. Pilot-wire protection scheme is most economical and provides high

speed relaying for .
a) Sho rt le ngt h o f lines up to 15 km.

b) Medium length of lines up to 60 km
c) Long length of lines up to 200 km.
d) All of the
above. Ans:
191. Adjustable resistors are connected in the pilot wires in order to .
a) Change the phase of the current flowing through the relay.

b) Get equipo t ent ia l po int s o n pilo t w ir e
c) Reduce the current flowing through the relay
d) None of the
above Ans:
192. In a balanced voltage pilot-wire protection scheme if the pilot-circuit gets

opened, the
relay will .
a) Fa il to t r ip o n int er na l fau lt s.
b) Trip on full load.
c) Trip instantaneously on external faults.
d) None of the
above Ans:
193. In a balanced voltage pilot-wire protection scheme, if the pilot-circuit gets

short- circuited,
the relay will .
a) Fail to trip on internal faults.

b) Fail to trip on external
faults. c) Tr ip o n fu ll- lo
ad.
d) Trip
instantaneously.
Ans:
194. Carrier current protection scheme is normally used for protection of HV
cables only
.
a) HV transmission lines only.

b) Bot h ( a) & ( b).
c)
No
ne
of
the
abo
ve.
Ans
195. The frequency of carrier in the carrier current pilot scheme is in the range of .
a) 1 kHz to 10 kHz.
b) 10 kHz to 25 kHz.
c) 25 kHz to 50
kHz. d) 50 kHz to
500 kHz.
Ans:
196. T
he frequency of carrier transmitted by micro-wave pilot is in the range of .
a) 1,000 kHz to 1,500 kHz.

b) 2,000 kHz to 5,000 kHz.
c) 900 MHz to 6,000 MHz
d) 10,000 MHz to 15,000 MHz
Ans:
197. In carrier current protection the purpose of wave trap is for .
a) Trapping power frequency waves

b) Trapping high frequency waves entering into generator / transformer unit
c) Both (a) and (b)
d) None of the
above Ans:
198. In an overhead transmission line, wave traps are used for the detection of .
a) The fault current signals.

b) The fault voltage
signals. c) Car r ier s ig
na ls.
d)
Fau
lt
po
wer
sig
nal
Ans
:
199. Coupling capacitors used in carrier protection have values usually
in the range of .
a) 1 to 20 µF.
b) 100 to 500 µF
c) 0.01 to 0.1 µF.
d) 1,
000
to
5,
000
pF
Ans
200. The line trap in the case of carrier current pilot consists of .
a) Series L-C circuit.

b) Series R-L-C
circuit. c) Par alle l
L- C c ir cu it .
d)
Par
allel
R-C
circ
uit.
Ans
201. The line trap unit employed in carrier current relaying .
a) Offers high impedance to 50 Hz power frequency signals.

b) O ffer s hig h impeda nce t o car r ier fr eque nc y s ig na ls.
c) Offers low impedance to carrier frequency signals.
d) Offers low impedance to carrier frequency signals and high impedance
to 50 Hz power frequency signals.
Ans:
202. A line trap in a long transmission line is used to .
a) Improve the power factor.

b) Dampen the over-voltage oscillations.
c) Confine the carrier signals in the line.
d) Protect the line against direct
lightning stroke. Ans:
203. Line trap and coupling capacitors are used for carrier current
protection in which
.
a) Line trap has high impedance to 50 Hz signal but low impedance to

carrier current signal whereas a coupling capacitor has low impedance
to 50 Hz signal but high impedance to carrier signal
b) L ine t r ap has lo w impeda nc e to 50HZ s ig na l but hig h impeda
nce t o car r ier cur r ent s ig na l, w her e as a co upling capac it o r has
hig h i mp edance to 50 Hz sig na l but lo w impeda nc e to car r ier s
ig na l.
(c) Both the line trap and coupling capacitor have low impedance to 50
Hz signal but high impedance to carrier current signal.
(d) Both the line trap and coupling capacitor have high impedance to 50 Hz
signal but low impedance to carrier current signal.
Ans:
204. In a 3-step distance protection, the reach of the three zones of the relay at
the beginning
of the first line typically extends into .
a) 100% of the first line, 50% of the second line and 20% of the third
line.
b) 80% o f t he fir st line, 50% o f t he seco nd line a nd 20% o f t he
t hir d line.
c) 80% of the first line, 50% of the second line and 10% of
the third line.
d) 50% of the first line, 50% of second line and 20% of
the third line Ans:
205. First zone distance relay protects a transmission line section up to .
a) It’s full-length.
b) 50% of its full-length.
c) 25% of its full-
length d) 80% o f it
s fu ll- le ngt h.
Ans:
206. Distance protection scheme is preferred over graded lime-lag over-current

protection in HV and EHV lines because .
a) It is fa st er in o per at io n
b) It is simple
c) It is cheaper in cost.
d) All of the
above. Ans:
207. In distance protection of transmission line, with

the voltage at the relay point increase of distance
of fault point from the relay.
a) I ncr eases
b) Decreases
c) Remains constant
d) Drops to zero
instantaneously Ans:
208. Over-current protection responds to
a) I ncr ease in cur r e nt abo ve p ick - up va lu e
b) Single line to earth fault
c) Double line to earth fault
d) All of above
Ans:
209. The earth fault in stator causes
a) arcing to core
b) severe heating in conductors and thereby damaging the insulation
c) open circuit in the stator
d) bot h ( a) and (
b) Ans:
210. The overvoltage surges in power system may be caused by
a) lightning
b) resonance
c) switching
d) all o f t
hese Ans:
SWITCHGEAR & PROTECTION Multiple Choice Questions :-
1. The main function of a fuse is to
(a) protect the line
(b) open the circuit
(c) protect the appliance
(d) prevent excessive currents
(e) none of the above
Ans: d
2. On which of the following routine tests are conducted ?
(a) Oil circuit breakers
(b) Air blast circuit breakers
(c) Minimum oil circuit breakers
(d) All of the above
Ans: d
3. SF6 gas
(a) is yellow in colour
(b) is lighter than air
(c) is nontoxic
(d) has pungent small
Ans: c
4. The arcing contacts in a circuit breaker are made of

(a) copper tungsten alloy
(b) porcelain
(c) electrolytic copper
(d) aluminium alloy
Ans: a
5. Which of the following medium is employed for extinction of arc in air circuit breaker ?
(a) Water
(b) Oil
(c) Air
(d) SF6
Ans: c
6. With which of the following, a circuit breaker must be equipped for remote operation ?
(a) Inverse time trip
(b) Time-delay trip
(c) Shunt trip
(d) None of the above
(e) All of the above
Ans: c
7. Fault diverters are basically
(a) fuses
(b) relays
(c) fast switches
(d) circuit breakers
Ans: c
8. A thermal protection switch can protect against
(a) short-circuit
(b) temperature
(c) overload
(d) over voltage
Ans: c
9. Arc in a circuit behaves as
(a) a capackive reactance
(b) an inductive reactance
(c) a resistance increasing with voltage rise across the arc
(d) a resistance decreasing with voltage rise across the arc
Ans: d
10. Thermal circuit breaker has
(a) delayed trip action
(b) instantaneous trip action
(c) both of the above
(d) none of the above
Ans: a
SWITCHGEAR & PROTECTION Objective Questions
SWITCHGEAR & PROTECTION Mcqs
11. Relays can be designed to respond to changes in
(a) resistance, reactance or impedance
(b) voltage and current
(c) light intensity
(d) temperature
(e) all above
Ans: e
12. Overload relays are of…… type.
(a) induction
(b) solid state
(c) thermal
(d) electromagnetic
(e) all above
Ans: e
13. Thermal overload relays are used to protect the motor against over current due to
(a) short-circuits
(b) heavy loads
(c) grounds
(d) all of the above
Ans: b
14. Magnetic circuit breaker has trip action.
(a) delayed
(b) instantaneous
(c) both of the above
Ans: b
15. D.C. shunt relays are made of
(a) few turns of thin wire
(b) few turns of thick wire
(c) many turns of thin wire
(d) many turns of thick wire
Ans: c
16. The relay operating speed depends upon
(a) the spring tension
(b) the rate of flux built up
(c) armature core air gap
Ans: d
17. In order that current should flow without causing excessive heating or voltage drop, the relay
contacts should
(a) have low contact resistance
(b) be clean and smooth
(c) be of sufficient size and proper shape
(d) have all above properties
Ans: d
18. Circuit breakers usually operate under
(a) transient state of short-circuit current
(b) sub-transient state of short-circuit current
(c) steady state of short-circuit current
(d) after D.C. component has ceased
Ans: a
19. Circuit breakers are essentially
(a) current carrying contacts called electrodes
(b) arc extinguishers
(c) circuits to break the system
(d) transformers to isolate the two systems
(e) any of the above
Ans: a
20. The current zero interruption, in oil and air blast circuit breakers, is achieved by
(a) lengthening of the gap

(b) cooling and blast effect
(c) both (a) and (b)
(d) deionizing the oil with forced air
Ans: c
21. Air blast circuit breaker is used for
(a) over currents
(b) short duty
(c) intermittant duty
(d) repeated duty
Ans: d
22. An efficient and a well designed protective relaying should have
(a) good selectivity and reliability
(b) economy and simplicity
(c) high speed and selectivity
Ans: d
23. Burden of a protective relay is the power
(a) required to operate the circuit breaker
(b) absorbed by the circuit of relay
(c) developed by the relay circuit

Ans: b
24. Directional relays are based on flow of
(a) power
(b) current
(c) voltage wave
Ans: a
25. A differential relay measures the vector difference between
(a) two currents
(b) two voltages
(c) two or more similar electrical quantities
Ans: c
26. A transmission line is protected by
(a) inrush protection
(b) distance protection
(c) time graded and current graded over current protection
(d) both (b) and (c)
Ans: d
27. Large internal faults are protected by

(a) merz price percentage differential protection
(b) mho and ohm relays
(c) horn gaps and temperature relays
(d) earth fault and positive sequence relays
Ans: a
28. When a transmission line is energized, the wave that propagates on it is
(a) current wave only
(b) voltage wave only
(d) power factor wave only
Ans: c
29. Protective relays are devices that detect abnormal conditions in electrical circuits by measuring
(a) current during abnormal condition
(b) voltage during abnormal condition
(c) constantly the electrical quantities which differ during normal and abnormal conditions
Ans: c
30. The voltage appearing across the contacts after opening of the circuit breaker is called _voltage.
(a) recovery
(b) surge
(c) operating
(d) arc
Ans: a
31. Ionization in circuit breaker is facilitated by
(a) high temperature
(b) increase of mean free path
(c) increasing field strength
Ans: d
32. In a circuit breaker the basic problem is to
(a) maintain the arc
(b) extinguish the arc
(c) transmit large power
(d) emit the ionizing electrons
Ans: c
33. Overheating of relay contacts or contact born out is due to
(a) slow making and breaking of load circuit contacts
(b) foreign matter on the contact surface
(c) too low contact pressure
Ans: d
34. Interruption of large currents by relay requires

(a) arc suppressing blow out coils
(b) wide separation of the opened contacts
(c) high speed opening of contacts
Ans: d
35. Shunt capacitance is neglected while considering
(a) short transmission line
(b) medium transmission line
(c) long transmission line
(d) medium and long transmission lines
Ans: a
36. The arc voltage produced in A.C. circuit breaker is always
(a) in phase with the arc current
(b) lagging the arc current by 90″
(c) leading the arc current by 90°
Ans: a
37. The time of closing the cycle, in modern circuit breakers is
(a) 0.003 sec
(b) 0.001 sec
(c) 0.01 sec
(d) 0.10 sec

Ans: a
38. Insulation resistance of high voltage circuit breakers is more than
(a) 1 mega ohms
(b) 10 mega ohms
(c) 100 mega ohms
(d) 500 mega ohms
Ans: c
39. H.R.C. fuses provide best protection against
(a) overload
(b) reverse current
(c) open-circuits
(d) short-circuits
Ans: d
40. The ground wire should not be smaller than No copper.
(a) 2
(b) 4
(c) 6
(d) 10
Ans: d
41. The delay fuses are used for the protection of .

(a) motors
(b) power outlet circuits
(c) fluorescent lamps
(d) light circuits
Ans: a
42. Which of the following is the least expensive protection for overcurrent is low voltage system ?
(a) Rewireable fuse
(b) Isolator
(c) Oil circuit breaker
(d) Air break circuit breaker
(e) None of the above
Ans: a
43. Resistance grounding is used for voltage between
(a) 33kVto66kV
(b) HkVto33kV
(c) 3.3kVandllkV
Ans: c
44. The contacts of high voltage switches used in power system are submerged in oil. The main purpose
of the oil is to
(a) lubricate the contacts
(b) insulate the contacts from switch body
(c) extinguish the arc

Ans: c
45. In Railway applications circuit breaker is used.
(a) SFe
(b) bulk oil
(c) minimum oil
(d) air break
Ans:
46. To protect most of the electrical equipment handling low power, the types of relays used are
(a) thermocouple
(b) electronic and bimetallic
Ans: c
47. Wave trap is used to trap waves of
(a) power frequencies
(b) higher frequencies entering generator or transformer units
(c) either of the above
Ans: b
48. Ungrounded neutral transmission system is not recommended because of system
(a) insulation being overstressed due to over voltages
(b) insulation overstress may lead to failure and subsequent phase to phase faults
(c) being inadequately protected against ground fault
Ans: d
49. The reflection co-efficient at the open circuited end of a transmission line.
(a) zero
(b) infinity
(c) unity
Ans: c
50. For the protection of power station buildings against direct strokes the requirements are
(a) interception
(b) interception and conduction
(c) interception, conduction and dissipation
(d) interception, conduction, dissipation and reflection
Ans: c
51. The line insulation is the insulation level of the station equipment.
(a) less than
(b) same as
(c) more than
(d) proportional to
(e) not directly related with
Ans: e
52. The interaction between a transmission line and communication line is minimized by
(a) transposing transmission as well as communication lines
(b) increasing the height of the trans-mission line tower
(c) increasing the distance between the two lines
Ans: d
53. When a wave propagates on a transmission line, it suffers reflection several times at
(a) tapping
(b) load end
(c) sending end
(d) sending and other end
(e) all of the above
Ans: d
54. Which of the following statements is incorrect?
(a) Station batteries are used to operate relay only
(b) The lightning arresters are basically surge diverters
(c) An impedance relay has maximum fault current when fault occurs near the relay
(d) A high speed relay has an operation of 1 to 2 cycles

Ans: a
55. Discrimination between main and back up protection is provided by the use of relays which are
(a) fact
(b) sensitive
(c) slow
Ans: c
56. Induction cup relay is operated due to changes in
(a) current
(b) voltage
(c) impedance
Ans: d
57. A.C. network analyser is used to solve problems of
(a) load flow
(b) load flow and short-circuit
(c) load flow and stability
(d) load flow, short-circuit and stability
Ans: d
58. Which of the following statements is incorrect ?

(a) Lightning arrestors are used before the switchgear
(b) Shunt reactors are used as compensation reactors
(c) The peak short current is (1.8 xV2) times the A.C. component
(d) The MVA at fault is equal to base MVA divided by per unit equivalent fault reactance
Ans: a
59. Short-circuit currents are due to
(a) single phase to ground faults
(b) phase to phase faults
(c) two phase to ground faults
(d) three phase faults
(e) any of these
Ans: e
60. To reduce short circuit fault currents are used.
(a) reactors
(b) resistors
(c) capacitors
Ans: a
61. Bus coupler is very essential in arrangement
(a) single bus
(b) double bus, double breaker
(c) main and transfer bus

Ans: c
62. For cost and safety, the outdoor substations are installed for voltages above
(a) 11 kV
(b) 33 kV
(c) 60kV
(d) 110kV
Ans: b
63. The short circuit in any winding of the transformer is the result of
(a) mechanical vibration
(b) insulation failure
(c) loose connection
(d) impulse voltage
Ans: d
64. relays are used for phase faults on long line.
(a) Impedance
(b) Reactance
(c) Either of the above
Ans: a
65. For which of the following protection from negative sequence currents is provided ?
(a) Generators
(b) Motors
(c) Transmission line
(d) Transformers
Ans: a
66. relay is preferred for phase fault on short transmission line.
(a) Induction type
(b) Reactance
(c) Impedance
Ans: b
67. Distance relays are generally
(a) split-phase relays
(b) reactance relays
(c) impedance relays
Ans: d
68. For which of the following ratings of the transformer differential protection is recommended ?
(a) above 30 kVA.
(b) equal to and above 5 MVA
(c) equal to and above 25 MVA

Ans: b
69. A is used to measure the stator % winding temperature of the generator.
(a) thermocouple
(b) pyrometer
(c) resistance thermometer
(d) thermometer Ans: c
70. The under voltage relay can be used for
(a) generators
(b) busbars
(c) transformers
(d) motors
(e) all of the above Ans: e
71. The relay with inverse time characteristic will operate within
(a) 1.5 sec
(b) 5 to 10 sec
(c) 5 to 20 sec
(d) 20 to 30 sec
(e) none of the above Ans: b

72. The single phasing relays are used for the protection of
(a) single phase motors only
(b) two phase motors only
(c) two single phase motors running in parallel
(d) three phase motors
Ans: d
73. Which of the following devices will receive voltage surge first travelling on the transmission line ?
(a) Lightning arresters
(b) Relays
(c) Step-down transformer
(d) Switchgear
Ans: a
74. Which of the following parameter can be neglected for a short line ?
(a) Inductance
(b) Capacitance
(c) Resistance
(d) Reactance
Ans: b
75. Series reactors should have

(a) low resistance
(b) high resistance
(c) low impedance
(d) high impedance
Ans: a
76. Which of the following circuit breakers has high reliability and minimum maintenance ?
(a) Air blast circuit breakers
(b) Circuit breaker with SF6 gas
(c) Vacuum circuit breakers
(d) Oil circuit breakers
Ans: b
77. Arc in a circuit breaker is interrupted at

(a) zero current
(b) maximum current
(c) minimum voltage
(d) maximum voltage
Ans: a
78. transmission line has reflection coefficient as one.

(a) Open circuit
(b) Short-circuit
(e) Long
Ans: a
79. What will be the reflection co-efficient of the wave of load connected to transmission line if surge impedance of the
line is equal to load ?
(a) Zero
(b) Unity
(c) Infinity
Ans: a
80. The inverse definite mean time relays are used for over current and earth fault protection of transformer against
(a) heavy loads
(b) internal short-circuits
(c) external short-circuits
Ans: b
81. Over voltage protection is recommended for

(a) hydro-electric generators
(b) steam turbine generators
(c) gas turbine generators
Ans: d
82. Air blast circuit breakers for 400 kV power system are designed to operate in
(a) 100 microsecond
(b) 50 millisecond
(c) 0.5 sec
(d) 0.1 sec
Ans: b
83. Overfluxing protection is recommended for

(a) distribution transformer
(b) generator transformer of the power plant
(c) auto-transformer of the power plant
(d) station transformer of the power plant
Ans: b
84. Series capacitors are used to

(a) compensate for line inductive reactance
(b) compensate for line capacitive reactance
(c) improve line voltage
Ans: a
85. Admittance relay is _______ relay.

(a) impedance
(b) directional
(c) non-directional
Ans: b
86. The material used for fuse must have

(a) low melting point and high specific resistance
(b) low melting point and -low specific resistance
(c) high melting point and low specific resistance
(d) low melting point and any specific resistance
Ans: a
87. If the fault occurs near the impedance relay, the VII ratio will be
(a) constant for all distances
(b) lower than that of if fault occurs away from the relay
(c) higher than that of if fault occurs away from the relay
Ans: b
88. The torque produced in induction type relay (shaded pole structure) is
(a) inversely proportional to the current
(b) inversely proportional to the square of the current
(c) proportional to the current
(d) proportional to square of the current
Ans: b
89. The steady state stability of the power system can be increased by
(a) connecting lines in parallel
(b) connecting lines in series
(e) using machines of high impedance
(d) reducing the excitation of machines
Ans: a
90. The inductive interference between power and communication line can be minimized by
(a) transposition of the power line
(b) transposition of the communication line
(d) increasing the distance between the conductors
Ans: c
91. The power loss is an important factor for the design of

(a) transmission line
(b) motor
(c) generator
(d) feeder
Ans: a
92. A fuse is connected

(a) in series with circuit
(b) in parallel with circuit
(c) either in series or in parallel with circuit
Ans: a
93. H.R.C. fuse, as compared to a rewirable fuse, has

(a) no ageing effect
(b) high speed of operation
(c) high rupturing capacity
Ans: d
94. The fuse rating is expressed in terms of

(a) current
(b) voltage
(c) VAR
(d) kVA
Ans: a
95. The fuse blows off by

(a) burning
(b) arcing
(c) melting
Ans: c
96. On which of the following effects of electric current a fuse operates ?

(a) Photoelectric effect
(b) Electrostatic effect
(c) Heating effect
(d) Magnetic effect
Ans: c
97. An isolator is installed

(a) to operate the relay of circuit breaker
(b) as a substitute for circuit breaker
(c) always independent of the position of circuit breaker
(d) generally on both sides of a circuit breaker
Ans: d
98. A fuse in a motor circuit provides protection against

(a) overload
(b) short-circuit and overload
(c) open circuit, short-circuit and overload
Ans: b
99. Protection by fuses is generally not used beyond

(a) 20 A
(b) 50 A
(c) 100 A
(d) 200 A
Ans: c
100. A fuse is never inserted in

(a) neutral wire
(b) negative of D.C. circuit
(c) positive of D.C. circuit
(d) phase dine
Ans: a
101. Oil switches are employed for

(a) low currents circuits
(b) low voltages circuits
(c) high voltages and large currents circuits
(d) all circuits
Ans: c
102. A switchgear is device used for

(a) interrupting an electrical circuit
(b) switching an electrical circuit 111.
(c) switching and controlling an electrical circuit
(d) switching, controlling and protecting the electrical circuit and equipment
Ans: d
103. The fuse wire, in D.C. circuits, is inserted in
(a) negative circuit only
(b) positive circuit only
(d) either (a) or (b)
Ans: c
104. By which of the following methods major portion of the heat generated in a H.R.C. fuse is dissipated ?
(a) Radiation
(b) Convection
(c) Conduction
(d) All of the above
Ans: c
105. A short-circuit is identified by

(a) no current flow
(b) heavy current flow
(c) voltage drop
(d) voltage rise
Ans: b
106. The information to the circuit breaker under fault conditions is provided by
(a) relay
(b) rewirable fuse
(c) H.R.C. only
Ans: a
107. To limit short-circuit current in a power system are used.

(a) earth wires
(b) isolators
(c) H.R.C. fuses
(d) reactors
Ans: d
109. A balanced 3-phase system consists of

(a) zero sequence currents only
(b) positive sequence currents only
(c) negative and zero sequence currents
(d) zero, negative and positive sequence currents
Ans: b
110. In a single bus-bar system there will be complete shut down when
(a) fault occurs on the bus itself
(b) fault occurs on neutral line
(c) two or more faults occur simultaneously
(d) fault occurs with respect to earthing
Ans: a

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1.

Ionization in circuit breakers is facilitated by

2. Arc interruption is done by

3. Part of circuit breaker helpful in breaking the current is

4. Desired tripping of a circuit breaker is

5. Arcing time is the time between

6. For single frequency transients, ratio of peak restriking voltage to time

7. Time between energisation of trip coil and separation of contacts is called

8. In circuit breaker, to facilitate arc quenching, dielectric strength can be

9. Rate of rise restriking voltage depends upon

10. An ideal circuit breaker should offer

11. Interrupting a low inductive current may lead to

12. Instantaneous voltage in a circuit breaker depends upon

13. Current chopping can be avoided by

16. Which of the following is not a protective gear?

17. Difficulty of performing the circuit breaking operation is a function of

18. When contacts of circuit breaker opens

19. A.C. air break circuit breakers are used for

20. Quantity of oil in bulk oil circuit breakers increases with

21. Air blast circuit breakers are preferred for

22. Rating of circuit breaker depends upon

23. Phenomenon of arc interruption takes place at

24. Symmetrical breaking current is

25. Over voltage may be due to

26. In vacuum breakers, current wave

27. In oil circuit breakers, dielectric strength of oil should be

28. Main disadvantage (s) of oil circuit breaker is that it

29. Breaker should adjust itself to

30. At higher currents, the switchgear exhibit

31. Plain circuit breaker can’t be used for voltage above

ACA – R Academic Year: 2019 -20

Ques.1. The main function of a fuse is to

Answer.3. Prevent Excessive current

Ques.2. On which of the following routine tests are conducted?

Answer.4. All of the above

Ques.3. SF6 gas

Ques.4. The arcing contacts in a circuit breaker are made of

Answer.1. Copper tungsten alloy

Answer.3. Shunt trip

Ques.7. A protective device, which reduces the steepness of wavefront of a surge by

Answer.2. Surge absorber

Ques.8. A thermal protection switch can protect against

Answer.3. A resistance increasing with voltage rise across the arc

Ques.10. The thermal circuit breaker has

Answer.1. Delayed trip action

Ques.11. Relays can be designed to respond to changes in

Answer.4. All of the above

Ques.12. Overload relays are of type.

Answer.4. All of the above

Ques.14. The magnetic circuit breaker has trip action.

Ques.15. D.C. shunt relays are made of

Answer.3. Many turns of thin wire

Ques.16. The function of the circuit breaker is

Answer.1. To safeguard the circuit

Answer.4. Have all above properties

Ques.18. Circuit breakers usually operate under

Answer.1. Transient state of short-circuit current

Ques.19. Circuit breakers are essentially

Answer.1. Current carrying contacts called electrodes