ELECTRICAL INTERVIEW AND EXAM PREPARATION: July 2016

CIRCUIT BREAKER-2

16.Out of the following circuit breakers, which one has the lowest voltage range ?
(A) Air-break circuit breaker
(B) Tank type oil circuit breaker
(C) Air-blast circuit breaker
(D) SF_6 circuit breaker.
Answer
A

17.Which of the following circuit breaker can be installed on 400 kV line
(A) Tank type oil circuit breaker
(B) Miniature circuit breaker
(C) Vacuum circuit breaker
(D) Air blast circuit breaker.
Answer
D

18.In a vacuum circuit breaker, the vacuum is of the order of
(A) 10mm Hg
(B)10^-2 mmHg
(C) l0^-6 mmHg
(D)10^-9 mmHg.
Answer
D

19.In modem EHV circuit breakers, the operating time between instant of receiving trip signal and final contact separation is, of the order of
(A) 0.001 sec
(B) 0.015 sec
(C) 0.003 sec
(D) 0.03 sec.
Answer
D

20.In a HRC fuse the time between cut-off and final current zero, is known as
(A) total operating time
(B) arcing time
(C) pre-arcing time
(D) any of the above.
Answer
B

21.Fusing factor for a HRC fuse is
(A) Minimum fusing current / Current rating
(B) Minimum fusing current / Minimum rupturing time
(C) Maximum fusing current / Minimum fusing current
(D) Minimum fusing current / Prospective current of circuit.
Answer
A

22.Which of the following circuit breakers does not use pneumatic operating mechanism
(A) Air blast circuit breaker
(B) SF_6 blast circuit breaker
(C) Air break circuit breaker
(D) Bulk-oil circuit breaker.
Answer
D

23.The contact resistance of a circuit breaker is. of the order of
(A) 20 micro ohms ± 10
(B) 20milli ohms ± 10
(C) 20 ohms ± 10
(D) 200 ohms ± 10.
Answer
A

24.The insulation resistance of high voltage circuit breaker is
(A) 1k Ohm
(B) 10 k Ohm
(C) 20 Mega ohms
(D) 2000 Mega ohm.
Answer
D

25.There is definite objection to use of which of the following medium for extinguishing the arc in case of a circuit breaker ?
(A) Air
(B) SF_6 gas
(C) Vacuum
(D) Water.
Answer
D

26.In a circuit breaker if the insulation resistance between phase terminal and earthed frame is less than the specified limit, the
probable cause could be
(A) moisture
(B) dirty insulation surface
(C) carbon or copper particles sticking to the internal surface
(D) any of the above.
Answer
D

27.If a circuit breaker does not operate on electrical compound, the probable reason could be
(A) spring defective
(B) trip circuit open
(C) trip latch defective
(D) any of the above.
Answer
D

28.The normal frequency rms voltage that appears across the breaker poles after final arc extinction has occurred, is
(A) recovery voltage
(B) re striking voltage
(C) supply voltage
(D) peak voltage.
Answer
A

29.The transient voltage that appears across the contacts at the instant of arc extinction is called
(A) recovery voltage
(B) re striking voltage
(C) supply voltage
(D) peak voltage.
Answer
B

30.In a circuit breaker the active recovery voltage depends upon
(A) power factor
(B) armature reaction
(C) circuit conditions
(D) all of the above.
Answer
D

CIRCUIT BREAKER-1

1.A circuit breaker is
(A) power factor correcting device
(B) a device to neutralize the effect of transients
(C) a waveform correcting device
(D) a current interrupting device.
Answer
D

2.The function of protective relay in a circuit breaker is
(A) to each any stray voltages
(B) to close the contacts when the actuating quantity reaches a certain predetermined value
(C) to limit arcing current during the operation of circuit breaker
(D) to provide additional safety in the operation of circuit breaker.
Answer
B

3.Low voltage circuit breakers have rated voltage of less than
(A) 220 V
(B) 400V
(C) 1000 V
(D) 10,000 V.
Answer
C

4.The fault clearing time of a circuit breaker is usually
(A) few minutes
(B) few seconds
(C) one second
(D) few cycles of supply voltage.
Answer
D

5.The medium employed for extinction of arc in air circuit breaker is
(A) SF_6
(B) Oil
(C) Air
(D) Water.
Answer
C

6.Which of the following circuit breakers is preferred for EHT application
(A) Air blast circuit breakers
(B) Minimum oil circuit breakers
(C) Bulk oil circuit breakers
(D) SF_6 oil circuit breakers.
Answer
D

7.For high voltage, ac circuit breakers, the rated short circuit current is passed for
(A) 0.01 sec
(B) 0.1 sec
(C) 3 seconds
(D) 30 seconds.
Answer
C

8.Which of the following is not a type of the contactor for circuit breakers ?
(A) Electro-magnetic
(B) Electro-pneumatic
(C) Pneumatic
(D) Vacuum.
Answer
D

9.Interrupting medium in a contactor may be
(A) air
(B) oil
(C) SF_6 gas
(D) any of the above.
Answer
D

10.In air blast circuit breakers, the pressure of air is of the order of
(A) 100 mm Hg
(B) 1 kg/cm^2
(C) 20 to 30 kg/cm^2
(D) 200 to 300 kg/cm^2 .
Answer
C

11.SF6 gas is
(A) sulphur fluoride
(B) sulphur difluoride
(C) sulphur hexafluorine
(D) sulphur hexafluoride.
Answer
D

12.SF6 gas
(A) is yellow in color
(B) has pungent odor
(C) is highly toxic
(D) is non-inflammable.
Answer
D

13.SF6 gas
(A) is lighter than hydrogen
(B) is lighter than air
(C) has density 2-times as compared to that of air
(D) has density 5 limes as compared to that of air.
Answer
D

14.The pressure of SF_6 gas in circuit breakers is of the order of
(A) 100 mm Hg
(B) 1 kg/cm^2
(C) 3 to 5 kg/cm^2
(D) 30 to 50 kg/cm^2 .
Answer
C

15. While selecting a gas for circuit breaker, the property of gas
that should be considered is
(A) high dielectric strength
(B) non-inflammability
(C) non-toxicity
(D) all of the above.
Answer:D

SWITCHGEAR AND PROTECTION MCQ-1

1. In a circuit breaker the current which exists at the instant of
contact separation is known as....

*breaking current
* surge current
* recovery current
* re striking current
* The Right Answer: breaking current

2. Bucholz relay used on..

* Air cooled transformer
* oil cooled transformer
* welding transformer
* All of above
* The Right Answer: oil cooled transformer

3. The SF_6 gas is...

* non poisonous
* insulating properties
* non inflammable
* none of above
* The Right Answer: non inflammable

4. The rating of a wire is always expressed in

* Ampere
* Ampere-volt
* kW
* all of above
* The Right Answer: Ampere

5. Oil immersion of contacts is the method of ...

* arc prevention
* de ionization
* arc dispersion
* none of above.
* The Right Answer: arc dispersion

6. Air blast circuit breakers for 400 kV. Power system are designed to
operate in

* 50 micro seconds
* 50 milli seconds
* both A and B
* none of above
* The Right Answer: 50 milli seconds

7. Which of the following contact point metals has the highest melting
point ?

* silver
* Copper
* Tungsten
* Gold
* The Right Answer: Tungsten

8. HRC fuses are....

* Holding and Resisting current fuses
* High Rating fuse
* High Rupturing Capacity fuse
* all of above
* The Right Answer: High Rupturing Capacity fuse

9. A material best suited for manufacturing of fuse wire is...

* Aluminium
* Copper
* silver
* all of above
* The Right Answer: silver

10. A fuse is normally a ...

* voltage limiting device
* current limiting device
* power limiting device
* all of above
* The Right Answer: current limiting device

11. The basic function of a circuit breaker is to.

* extinguish the arc
* arc produce
* ionize the surrounding air
* none of above
* The Right Answer: extinguish the arc

12. A differential relay measures the vector difference between.

* two voltages
* two or more similar electrical quantities
* two current
* none of above
* The Right Answer: two or more similar electrical quantities

13. Thermal overload relays are used to protect the motor against over
current due to.

* heavy load
* over heat
* Short Circuit
* all of above
* The Right Answer: all of above

14. Breaking capacity of the circuit breaker is usually expressed in.

* Kilo-Ampere
* MVA
* KV
* kW
* The Right Answer: MVA

15. Which of the following circuit breakers produce least arc energy?

* Air blast
* Oil Circuit breaker
* Minimum oil
* None of above
* The Right Answer: Air blast

16. Which of the following is not a part of the circuit breaker ?

* conservator
* Fixed and moving contacts
* Explosion pot
* Operating mechanism.
* The Right Answer: conservator

17. A Merz-price protection is suitable for....

* Transformer
* Alternator
* Motor
* transmission line
* The Right Answer: Alternator

18. Which relay is used for transformer protection?

* Translay relay
* differential relay
* buchholz relay
* none of above.
* The Right Answer: buchholz relay

19. Which relay is used for feeders ?

* Translay relay
* differential relay
* MHO realy
* none of above
* The Right Answer: Translay relay

20. The over-voltage surges in power systems may be caused by...

* switching
* lightning
* resonance
* all of above
* The Right Answer: all of above

21. In a circuit breaker the current which exists at the instant of
contact separation is known as

* breaking current
* recovery current.
* surge current.
* all of above
* The Right Answer: breaking current

22. Oil immersion of contacts is the method of

* arc dispersion
* de ionization
* arc prevention
* all of above
* The Right Answer: arc dispersion

23. The arc voltage produced in the circuit breaker is always...

* leading the arc current by 90°
* lagging the arc current by 90° .
* in phase with arc current
* none of above
* The Right Answer: in phase with arc current

24. Sparking occurs when a load is switched off because the circuit has

* high capacitance
* high inductance
* high resistance.
* all of above
* The Right Answer: high inductance

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SWITCH GEAR AND PROTECTION IMPORTANT MCQ

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
(e) none of the above
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

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
(d) none 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
(d) all of the above
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

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
(e) none of the above
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
(d) all of the above
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
(d) none of the above
Ans: b

24. Directional relays are based on flow of
(a) power
(b) current
(c) voltage wave
(d) all of the above
Ans: a

25. A differential relay measures the vector difference between
(a) two currents
(b) two voltages
(c) two or more similar electrical quantities
(d) none of the above
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)
(e) none of the above
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
(c) both (a) and (b)
(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
(d) none of the above
Ans: c

30. The voltage appearing across the contacts after opening of the
circuit breaker is calledvoltage.
(a) recovery
(b) surge
(c) operating
(d) arc
(e) none of the above
Ans: a

31. 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
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
(d) all of the above
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
(d) all of the above
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°
(d) none of the above
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
(e) none of the above
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
(d) none of the above
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
(d) all of the above
(e) none of the above
Ans: c

45. In Railway applications circuit breaker is used.
(a) SFe
(b) bulk oil
(c) minimum oil
(d) air break
Ans:a

46. To protect most of the electrical equipment handling low power, the
types of relays used are
(a) thermocouple
(b) electronic and bimetallic
(c) both (a) and (b)
(d) none of the above
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
(d) none 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
(d) all of the above
Ans: d

49. The reflection co-efficient at the open circuited end of a
transmission line.
(a) zero
(b) infinity
(c) unity
(d) none of the above
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
(e) none of the above
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
(d) all of the above
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
(d) none of the above
Ans: c

56. Induction cup relay is operated due to changes in
(a) current
(b) voltage
(c) impedance
(d) all of the above
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
(e) none of the above
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
(d) none of the above
Ans: a

61. Bus coupler is very essential in arrangement
(a) single bus
(b) double bus, double breaker
(c) main and transfer bus
(d) all of the above
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
(d) None 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
(d) None of the above
Ans: b

67. Distance relays are generally
(a) split-phase relays
(b) reactance relays
(c) impedance relays
(d) none of the above
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
(d) none of the above
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
(d) None of the above
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
(d) None of the above
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
(d) all of the above
Ans: b

81. Over voltage protection is recommended for
(a) hydro-electric generators
(b) steam turbine generators
(c) gas turbine generators
(d) all of the above
(e) none of the above
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
(d) none of the above
Ans: a

85. Admittance relay is ___ relay.
(a) impedance
(b) directional
(c) non-directional
(d) none of the above
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
(d) none of the above
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
(e) none of the above
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
(c) both (a) and (b)
(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
(d) none of the above
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
(d) all of the above
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
(d) none of the above
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
(d) none of the above
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
(c) both (a) and (b)
(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
(d) all of the above
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

TRANSMISSION AND DISRIBUTION MOST IMPORTANT MCQ

1. By which of the following systems electric power may be transmitted ?
(a) Overhead system
(b) Underground system
(c) Both (a) and (b)
(d) None of the above
Ans: c

2 are the conductors, which connect the consumer’s terminals to the
distribution
(a) Distributors
(b) Service mains
(c) Feeders
(d) None of the above
Ans: b

3. The underground system cannot be operated above
(a) 440 V
(b) 11 kV
(c) 33 kV
(d) 66 kV
Ans: d

4. Overhead system can be designed for operation up to
(a) 11 kV
(b) 33 kV
(c) 66 kV
(d) 400 kV
Ans: c

5. If variable part of annual cost on account of interest and
depreciation on the capital outlay is equal to the annual cost of
electrical energy wasted in the conductors, the total annual cost will
be minimum and the corresponding size of conductor will be most
economical. This statement is known as
(a) Kelvin’s law
(b) Ohm’s law
(c) Kirchhoffs law
(d) Faraday’s law
(e) none of the above
Ans: a

6. The wooden poles well impregnated with creosite oil or any
preservative compound have life
(a) from 2 to 5 years
(b) 10 to 15 years
(c) 25 to 30 years
(d) 60 to 70 years
Ans: c

7. Which of the following materials is not used for transmission and
distribution of electrical power ?
(a) Copper
(b) Aluminium
(c) Steel
(d) Tungsten
Ans: d

8. Galvanised steel wire is generally used as
(a) stay wire
(b) earth wire
(c) structural components
(d) all of the above
Ans: d

9. The usual spans with R.C.C. poles are
(a) 40—50 meters
(b) 60—100 meters
(c) 80—100 meters
(d) 300—500 meters
Ans: c

10. The corona is considerably affected by which of the following ?
(a) Size of the conductor
(b) Shape of the conductor
(c) Surface condition of the conductor
(d) All of the above
Ans: d

11. Which of the following are the constants of the transmission lines ?
(a) Resistance
(b) Inductance
(c) Capacitance
(d) All of the above
Ans: d

12. 310 km line is considered as
(a) a long line
(b) a medium line
(c) a short line
(d) any of the above
Ans: a

13. The phenomenon qf rise in voltage at the receiving end of the
open-circuited or lightly loaded line is called the
(a) Seeback effect
(b) Ferranti effect
(c) Raman effect
(d) none of the above
Ans: b

14. The square root of the ratio of line impedance and shunt admittance
is called the
(a) surge impedance of the line
(b) conductance of the line
(c) regulation of the line
(d) none of the above
Ans: a

15. Which of the following is the demerit of a ‘constant voltage
transmission system’ ?
(a) Increase of short-circuit current of the system
(b) Availability of steady voltage at all loads at the line terminals
(c) Possibility of better protection for the line due to possible use of
higher terminal reactants
(d) Improvement of power factor at times of moderate and heavy loads
(e) Possibility of carrying increased power for a given conductor size
in case of long-distance heavy power transmission
Ans: a

16. Low voltage cables are meant for use up to
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV
Ans: e

17. The operating voltage of high voltage cables is up to
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV
Ans: d

18. The operating voltage of supertension cables is up to
(a) 3.3 kV
(b) 6.6 kV
(c) 11 kV
(d) 33 kV
Ans: d

19. The operating voltage of extra high tension cables is upto
(a) 6.6 kV
(b) 11 kV
(c) 33 kV
(d) 66 kV
(e) 132 kV
Ans: d

20. Which of the following methods is used for laying of underground
cables ?
(a) Direct laying
(b) Draw-in-system
(c) Solid system
(d) All of the above
Ans: d

21. Which of the following is the source of heat generation in the cables ?
(a) Dielectric losses in cable insulation
(b) losses in the conductor
(c) Losses in the metallic sheathings and armourings
(d) All of the above
Ans:d

22. Due to which of the following reasons the cables should not be
operated too hot ?
(a) The oil may loose its viscosity and it may start drawing off from
higher levels
(b) Expansion of the oil may cause the sheath to burst
(c) Unequal expansion may create voids in the insulation which will lead
to ionization
(d) The thermal instability may rise due to the rapid increase of
dielectric losses with temperature
(e) All of the above
Ans: e

23. Which of the following D.C. distribution system is the simplest and
lowest in first cost ?
(a) Radial system
(b) Ring system
(c) Inter-connected system
(d) None of the above
Ans: a

24. A booster is a
(a) series wound generator
(b) shunt wound generator
(c) synchronous generator
(d) none of the above
Ans: a

25. Besides a method of trial and error, which of the following methods
is employed for solution of network problems in interconnected system ?
(a) Circulating current method
(b) Thevenin’s theorem
(c) Superposition of currents
(d) Direct application of Kirehhoffs laws
(e) All of the above
Ans: e

26. Which of the following faults is most likely to occur in cables ?
(a) Cross or short-circuit fault
(b) Open circuit fault
(c) Breakdown of cable insulation
(d) All of the above
Ans:d

27. The cause of damage to the lead sheath of a cable is
(a) crystallisation of the lead through vibration
(b) chemical action on the lead when buried in the earth
(c) mechanical damage
(d) all of the above
Ans:d

28. The voltage of the single phase supply to residential consumers is
(a) 110 V
(b) 210 V
(c) 230 V
(d) 400 V
Ans: c

29. Most of the high voltage transmission lines in India are
(a) underground
(b) overhead
(c) either of the above
(d) none of the above
Ans: b

30. The distributors for residential areas are
(a) single phase
(b) three-phase three wire
(c) three-phase four wire
(d) none of the above
Ans: c

31. The conductors of the overhead lines are
(a) solid
(b) stranded
(c) both solid and stranded
(d) none of the above
Ans:b

32. High voltage transmission lines use
(a) suspension insulators
(b) pin insulators
(c) both (a) and (b)
(d) none of the above
Ans: a

33. Multicore cables generally use
(a) square conductors
(b) circular conductors
(c) rectangular conductors
(d) sector-shaped conductors
(e) none of the above
Ans: d

34. Distribution lines in India generally use
(a) wooden poles
(b) R.C.C. poles
(c) steel towers
(d) none of the above
Ans: b

35. The material commonly used for insulation in high voltage cables is
(a) lead
(b) paper
(c) rubber
(d) none of the above
Ans: b

36. The loads on distributors systems are generally
(a) balanced
(b) unbalanced
(c) either of the above
(d) none of the above
Ans: b

37. The power factor of industrial loads is generally
(a) unity
(b) lagging
(c) leading
(d) zero
Ans: b

38. Overhead lines generally use
(a) copper conductors
(b) all aluminium conductors
(c) A.C.S.R. conductors
(d) none of these
Ans: c

39. In transmission lines the cross-arms are made of
(a) copper
(b) wood
(c) R.C.C.
(d) steel
Ans: d

40. The material generally used for armour of high voltage cables is
(a) aluminium
(b) steel
(c) brass
(d) copper
Ans: b

41. Transmission line insulators are made of
(a) glass
(b) porcelain
(c) iron
(d) P.V.C.
Ans:b

42. The material commonly used for sheaths of underground cables is
(a) lead
(b) rubber
(c) copper
(d) iron
Ans: a

43. The minimum clearance between the ground and a 220 kV line is about
(a) 4.3 m
(b) 5.5 m
(c) 7.0 m
(d) 10.5 m
Ans: c

44. The spacing between phase conductors of a 220 kV line is
approximately equal to
(a) 2 m
(b) 3.5 m
(c) 6 m
(d) 8.5 m
Ans: c

45. Large industrial consumers are supplied electrical energy at
(a) 400 V
(b) 11 kV
(c) 66 kV
(d) 400 kV
Ans: c

46. In a D.C. 3-wire distribution system, balancer fields are
cross-connected in order to
(a) boost the generated voltage
(b) balance loads on both sides of the neutral
(c) make both machine^ run as unloaded motors
(d) equalize voltages on the positive and negative outers
Ans:d

47. In a D.C. 3-wire distributor using balancers and having unequal
loads on the two sides
(a) both balancers run as generators
(b) both balancers run as motors
(c) balancer connected to lightly- loaded side runs as a motor
(d) balancer connected to heavily- loaded side runs as a motor
Ans:c

48. Transmitted power remaining the same, if supply voltage of a D.C.
2-wire feeder is increased 100 percent, saving in copper is
(a) 25 percent
(b) 50 percent
(c) 75 percent
(d) 100 percent
Ans: b

49. A uniformly-loaded D.C. distributor is fed at both ends with equal
voltages. As compared to a similar distributor fed at one end only, the
drop at the middle point is
(a) one-fourth
(b) one-third
(c) one-half
(d) twice
(e) none of the above
Ans: a

50. As compared to a 2-wire D.C. distributor, a 3-wire distributor with
same maximum voltage to earth uses only
(a) 31.25 percent of copper
(b) 33.3 percent of copper
(c) 66.7 percent of copper
(d) 125 percent of copper
Ans: a

51. Which of the following is usually not the generating voltage ?
(a) 6.6 kV
(b) 8.8 kV
(c) 11 kV
(d) 13.2 kV
Ans: b

52. For an overhead line, the surge impedance is taken as
(a) 20-30 ohms
(b) 70—80 ohms
(c) 100—200 ohms
(d) 500—1000 ohms
(e) none of the above
Ans: c

53. The presence of ozone due to corona is harmful because it
(a) reduces power factor
(b) corrodes the material
(c) gives odour
(d) transfer energy to the ground
(e) none of the above
Ans: b

54. A feeder, in a transmission system, feeds power to
(a) distributors
(b) generating stations
(c) service mains
(d) all of the above
Ans: a

55. The power transmitted will be maximum when
(a) corona losses are minimum
(b) reactance is high
(c) sending end voltage is more
(d) receiving end voltage is more
Ans: c

56. A 3-phase 4 wire system is commonly used on
(a) primary transmission
(b) secondary transmission
(c) primary distribution
(d) secondary distribution
Ans: d

57. Which of the following materials is used for overhead transmission
lines ?
(a) Steel cored aluminium
(b) Galvanised steel
(c) Cadmium copper
(d) Any of the above
Ans: d

58. Which of the following is not a constituent for making porcelain
insulators ?
(a) Quartz
(b) Kaolin
(c) Felspar
(d) Silica
Ans: d

59. There is a greater possibility of occurence of corona during
(a) dry weather
(b) winter
(c) summer heat
(d) humid weather
(e) none of the above
Ans: d

60. Which of the following relays is used on long transmission lines ?
(a) Impedance relay
(b) Mho’s relay
(c) Reactance relay
(d) None of the above
Ans: b

61. The steel used in steel cored conductors is usually
(a) alloy steel
(b) stainless steel
(c) mild steel
(d) high speed steel
(e) all of the above
Ans: c

62. Which of the following distribution systems is more reliable ?
(a) Radial system
(b) Tree system
(c) Ring main system
(d) All are equally reliable
Ans: c

63. Which of the following characteristics should the line supports for
transmission lines possess ?
(a) Low cost
(b) High mechanical strength
(c) Longer life
(d) All of the above
Ans: d

64. Transmission voltage of ll kV is normally used for distances upto
(a) 20—25 km
(b) 40—50 km
(c) 60—70 km
(d) 80—100 km
Ans: a

65. Which of the following regulations is considered best?
(a) 50%
(b) 20%
(c) 10%
(d) 2%
Ans: d

66. Skin effect is proportional to
(a) (conductor diameter)
(b) (conductor diameter)
(c) (conductor diameter)
(d) (conductor diameter)
(e) none of the above
Ans: c

67. A conductor, due to sag between two supports, takes the form of
(a) semi-circle
(b) triangle
(c) ellipse
(d) catenary
Ans: d

68. In AC.S.R. conductors, the insulation between aluminium and steel
conductors is
(a) insulin
(b) bitumen
(c) varnish
(d) no insulation is required
Ans: d

69. Which of the following bus-bar schemes has the lowest cost ?
(a) Ring bus-bar scheme
(b) Single bus-bar scheme
(c) Breaker and a half scheme
(d) Main and transfer scheme
Ans: b

70. Owing to skin effect
(a) current flows through the half cross-section of the conductor
(b) portion of the conductor near the surface carries more current and
core of the conductor carries less current
(c) portion of the conductor near the surface carries less current and
core of the conductor carries more cur¬rent
(d) any of the above
(e) none of the above
Ans: b

71. By which of the following methods string efficiency can be improved ?
(a) Using a guard ring
(b) Grading the insulator
(c) Using long cross arm
(d) Any of the above
(e) None of the above
Ans: d

72. In aluminium conductors, steel core is provided to
(a) compensate for skin effect
(b) neutralise proximity effect
(c) reduce line inductance
(d) increase the tensile strength
Ans: d

73. By which of the following a bus-bar is rated ?
(a) Current only
(b) Current and voltage
(c) Current, voltage and frequency
(d) Current, voltage, frequency and short time current
Ans: d

74. A circuit is disconnected by isolators when
(a) line is energized
(b) there is no current in the line
(c) line is on full load
(d) circuit breaker is not open
Ans: b

75. For which of the following equipment current rating is not necessary ?
(a) Circuit breakers
(b) Isolators
(c) Load break switch
(d) Circuit breakers and load break switches
Ans: b

76. In a substation the following equipment is not installed
(a) exciters
(b) series capacitors
(c) shunt reactors
(d) voltage transformers
Ans: a

77. Corona usually occurs when the electrostatic stress in air around
the conductor exceeds
(a) 6.6 kV (r.m.s. value)/cm
(b) 11 kV (r.m.s. value)/cm
(c) 22 kV (maximum value)/cm
(d) 30 kV (maximum value)/cm
Ans: d

78. The voltage drop, for constant voltage transmission is compensated
by installing
(a) inductors
(b) capacitors
(c) synchronous motors
(d) all of above
(e) none of the above
Ans: c

79. The use of strain type insulators is made where the conductors are
(a) dead ended
(b) at intermediate anchor towers
(c) any of the above
(d) none of the above
Ans: c

80. The current drawn by the line due to corona losses is
(a) non-sinusoidal
(b) sinusoidal
(c) triangular
(d) square
Ans: a

81. Pin type insulators are generally not used for voltages beyond
(a) 1 kV
(b) 11 kV
(c) 22 kV
(d) 33 kV
Ans: d

82. Aluminium has a specific gravity of
(a) 1.5
(b) 2.7
(c) 4.2
(d) 7.8
Ans: b

83. For transmission of power over a distance of 200 km, the
transmission voltage should be
(a) 132 kV
(b) 66 kV
(c) 33 kV
(d) 11 kV
Ans: a

84. For aluminium, as compared to copper, all the following factors have
higher values except
(a) specific volume
(6) electrical conductivity
(c) co-efficient of linear expansion
(d) resistance per unit length for same cross-section
Ans: b

85. Which of the following equipment, for regulating the voltage in
distribution feeder, will be most economical ?
(a) Static condenser
(b) Synchronous condenser
(c) Tap changing transformer
(d) Booster transformer
Ans: d

86. In a tap changing transformer, the tappings are provided on
(a) primary winding
(b) secondary winding
(c) high voltage winding
(d) any of the above
Ans: c

87. Constant voltage transmission entails the following disadvantage
(a) large conductor area is required for same power transmission
(b) short-circuit current of the system is increased
(c) either of the above
(d) none of the above
Ans: b

88. On which of the following factors skin effect depends ?
(a) Frequency of the current
(b) Size of the conductor
(c) Resistivity of the conductor material
(d) All of the above
Ans: d

89. The effect of corona can be detected by
(a) presence of ozone detected by odour
(b) hissing sound
(c) faint luminous glow of bluish colour
(d) all of the above
Ans: d

90. For transmission of power over a distance of 500 km, the
transmission voltage should be in the range
(a) 150 to 220 kV
(b) 100 to 120 kV
(c) 60 to 100 kV
(d) 20 to 50 kV
Ans: a

91. In the analysis of which of the following lines shunt capacitance is
neglected ?
(a) Short transmission lines
(b) Medium transmission lines
(c) Long transmission lines
(d) Medium as well as long transmission lines
Ans: a

92. When the interconnector between two stations has large reactance
(a) the transfer of power will take place with voltage fluctuation and noise
(b) the transfer of power will take place with least loss
(c) the stations will fall out of step be¬cause of large angular
displacement between the stations
(d) none of the above
Ans: c

93. The frequency of voltage generated, in case of generators, can be
increased by
(a) using reactors
(b) increasing the load
(c) adjusting the governor
(d) reducing the terminal voltage
(e) none of the above
Ans: c

94. When an alternator connected to the bus-bar is shut down the bus-bar
voltage will
(a) fall
(b) rise
(c) remain unchanged
(d) none of the above
Ans: c

95. The angular displacement between two interconnected stations is
mainly due to
(a) armature reactance of both alternators
(b) reactance of the interconnector
(c) synchronous reactance of both the alternators
(d) all of the above
Ans: a

96. Electro-mechanical voltage regulators are generally used in
(a) reactors
(b) generators
(c) transformers
(d) all of the above
Ans: b

97. Series capacitors on transmission lines are of little use when the
load VAR requirement is
(a) large
(b) small
(b) fluctuating
(d) any of the above
Ans: b

98. The voltage regulation in magnetic amplifier type voltage regulator
is effected by
(a) electromagnetic induction
(b) varying the resistance
(c) varying the reactance
(d) variable transformer
Ans: c

99. When a conductor carries more current on the surface as compared to
core, it is due to
(a) permeability variation
(b) corona
(c) skin effect
(d) unsymmetrical fault
(e) none of the above
Ans: c

100. The following system is not generally used
(a) 1-phase 3 wire
(b) 1-phase 4 wire
(c) 3-phase 3 wire
(d) 3-phase 4 wire
Ans: a

101. The skin effect of a conductor will reduce as the
(a) resistivity of conductor material increases
(b) permeability of conductor material increases
(c) diameter increases
(d) frequency increases
Ans: a

102. When a live conductor of public electric supply breaks down and
touches the earth which of the following will happen ?
(a) Current will flow to earth
(b) Supply voltage will drop
(c) Supply voltage will increase
(d) No current will flow in the conductor
(e) None of the above
Ans: a

50 IMPORTANT MCQ WITH ANS. ON TRANSFORMER

50 IMPORTANT MCQ ON TRANSFORMER

1.Oil is provided in an oil filled transformer for
A. Insulation
B. cooling
C. both cooling and insulation.
D. Lubrication

2) The basic function of transformer is to change?
A. the level voltage
B. the level frequency
C. power factor level
D. power level

3) Transformer is used for—
A. to step down voltage
B. to step up and step down primary voltage
C. to step up voltage
D. None of above

4) Breather is provided in a transformer to
A. Absorb moisture of air during breathing.
B. filter of transformer oil
C. provide cold air in transformer
D. None of above

5) The leakage flux in a transformer depends upon
A. the load current.
B. the frequency.
C. the mutual flux.
D. the applied voltage.

6) What kVA rating is required for a transformer
that must handle a maximum load current of 8 A
with a secondary voltage of 2 kV?
A. 32kv
B. 16kv
C. 4kv
D. 8kV

7) The copper loss of a transformer at full load is
40W. What would be at half load-
A. 20W
B. 80W
C. 40W
D. 10W

8) When a 6 V battery is connected across the
primary of a transformer with a turns ratio of 8,
the secondary voltage is
A. 48v
B. 6v
C. 8v
D. 0

9) The main purpose of performing open circuit
test in a transformer is to measure its–
A. core loss
B. copper loss
C. insulation resistance
D. total loss

10) When a 400Hz transformer is operated at 50
Hz, its KVA ratings is–
A. unaffected
B. reduced to 1/8
C. Increased by 8 times
D. None of above

11) What is the condition for maximum efficiency
of a transformer?
A. when copper loss = core loss
B. When transformer run by unity power
factor
C. when copper loss = eddy current loss
D. when copper loss = hysteresis loss

12) Lamination of transformer core is made of
A. cast iron
B. silicon steel.
C. cast steel
D. aluminium

13) Which of the following is minimized by
laminating the core of a transformer?
A. Eddy current loss.
B. Hysteresis loss.
C. Copper loss
D. Stray loss

14) Does the transformer draw any current when
secondary is open?
A. Yes
B. No

15) When the turns ratio of a transformer is 20
and the primary ac voltage is 12 V, the secondary
voltage is
A. 24v
B. 120v
C. 240v
D. 440v

16) The input power under no load condition of
transformer consists of
A. core losses and very small amount of
copper loss in primary.
B. copper loss in transformers.
C. core loss in transformers.
D. None of above.

17) Transformers operating in parallel will share
the load depending upon their-
A. rating
B. Percentage impedance.
C. Leakage reactance.
D. None of above

18) Which of the following is not a basic element
of a transformer?
A. primary winding
B. secondary winding
C. mutual flux
D. core

19) At relatively light load, transformer efficiency
is low because-
A. transformer losses are high
B. secondary output is low
C. fixed loss is high in proportion to the
output
D. Cu loss is small

20) A transformer transform-
A. voltage and currrent
B. voltage
C. current
D. frequency

21) When AC supply is given to the transformer,
the flux will depend on…….
A. Current
B. Voltage
C. Frequency
D. Voltage and Frequency

22) No-load test on a transformer is carried out to
determine-
A. copper loss
B. magnetising current and no-load current
C. magnetising current
D. all of above.

23) Which of the following losses varies with load
in transformer?
A. Copper loss.
B. Core loss
C. Transfomer all losses
D. None of above

24) A transfomer has negative voltage regulation
when its load power factor is–
A. lagging
B. leading
C. unity
D. None of above

25) The essential condition for parallel operation of
two single-phase transformer is that they should
have the same–
A. polarity
B. KVA ratings
C. voltage ratio
D. None of abobe

26) Which one is used for constant street light
load?
A. current transformer
B. Constant current transformer
C. power transformer
D. potential transformer

27) Which of the following losses remain constant
during normal operation of transformer?
A. Copper loss
B. Transformer all losses
C. Core loss
D. None of above

28) Iron loss in transformer can be determined
by…..
A. open circuit test.
B. short circuit test.

29) Transformer core are laminated in order to-
A. simplify it's construction
B. minimize eddy current loss
C. reduce cost
D. reduce hysteresis loss

30) The main purpose of performing short circuit
test in a transformer is to measure its–
A. Copper Loss
B. Core Loss
C. Total Loss
D. Insulation resistance

31) The path of a magnetic flux in a transformer
should have
A. low resistance
B. low reluctance
C. high resistance
D. high reluctance

32) No-load current in a transformer
A. lags behind the voltage by about 75°
B. leads the voltage by about 75°
C. lags behind the voltage by about 15°
D. leads behind the voltage by about 25°

33) Which of the following is not a part of
transformer?
A. Breather
B. Conservator
C. Exciter
D. Buchholz relay

34) While conducting short-circuit test on a
transformer the following side is short circuited
A. Low voltage side
B. High voltage side
C. Primary side
D. Secondary side

35) Which winding in a transformer has more
number of turns ?
A. Primary winding
B. Secondary winding
C. High voltage winding
D. Low voltage winding

36) In a given transformer for given applied
voltage, losses which remain constant irrespective
of load changes are
A. core losses
B. copper losses
C. both A and B
D. none of the above

37) Power transformers are designed to have
maximum efficiency at
A. 80% full load
B. 50% full load
C. nearly full load
D. no load

38) The maximum efficiency of a distribution
transformer is
A. at full load
B. at 70% full load
C. at 50% full load
D. at no load

39) Flash point of transformer insulating oil should
be more than
A. 100°C.
B. 140°C.
C. 45°C.
D. 35°C
.
40) Noise of transformer mainly due to
A. noise generated by cooling fans.
B. magnetostriction in iron core.
C. mechanical vibration.
D. all of above

41) The tap changer in an electrical power
transformer is provided on
A. LV winding.
B. HV winding.
C. either LV or HV winding.
D. both LV and HV winding.

42) The transformer ratings are usually expressed
in terms of
A. KVA
B. KW
C. KVAR
D. Volts

43) A Buchholz relay can be installed on-
A. welding transformers
B. air cooled transformers
C. oil cooled transformers
D. all of above

44) In a transformer the resistance between its
primary and secondary is
A. zero
B. infinite
C. 1 ohm
D. 10000 ohm

45) If the supply frequency to the transformer is
increased, the iron loss will
A. remain same
B. decrease
C. increase
D. any of the above

46) Which type of winding is used in 3phase shelltype
transformer ?
A. Cylindrical type
B. Circular type
C. Rectangular type
D. Sandwich type

47) The secondary winding of which of the
following transformers is always kept closed ?
A. CT
B. PT
C. Step-up transformer
D. Step-down transformer

48) The efficiency of two identical transformers
under load conditions can be determined by
A. back-to-back test
B. short circuit test
C. open circuit test
D. none of above

49) Which of the following loss in a transformer is
zero even at full load ?
A. Hysteresis loss
B. Eddy current loss
C. Core loss
D. Friction loss

50) If supply frequency of a transformer increases,
the secondary output voltage of the transformer -
A. remains same.
B. increases.
C. decreases.
D. any of the above