Transposition of The Communication Line
Transposition of The Communication Line
Transposition of The Communication Line
3.the arcing contacts in a circuit breaker are made of copper tungsten alloy.
5. The steady state stability of the power system can be increased by Connecting lines in
parallel .
6. The inductive interference between power and communication line can be minimized by
transposition of the power line and transposition of the communication line.
9. The time of closing the cycle, in modern circuit breakers is 0.003 sec .
11. Resistance grounding is used for voltage between 3.3kV and llkV .
12. Discrimination between main and back up protection is provided by the use of relays
which are slow .
13. Thermal overload relays are used to protect the motor against over current due to heavy
loads.
14. When a transmission line is energized, the wave that propagates on it is current and
voltage wave.
17. The inverse definite mean time relays are used for over current and earth fault
protection of transformer against internal short-circuits.
18. Which of the following devices will receive voltage surge first travelling on
the transmission line ?
Lightning arresters.
19. The relay with inverse time characteristic will operate within 5 to 10 sec.
20. Arc in a circuit behaves as a resistance decreasing with voltage rise across
the arc.
20. The reflection co-efficient at the open circuited end of a transmission line. Unity.
22. The ground wire should not be smaller than No __10____ copper.
25. The voltage appearing across the contacts after opening of the circuit breaker is
called______voltage. Recovery.
26. The material used for fuse must have low melting point and -low specific resistance
27. For cost and safety, the outdoor substations are installed for voltages above 33kv.
28. The torque produced in induction type relay (shaded pole structure) is
inversely proportional to the square of the current
29. 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 ? zero
30. Burden of a protective relay is the power absorbed by the circuit of relay
31. The line insulation is the insulation level of the station equipment.not directly
related with
33. The delay fuses are used for the protection of motors.
36. Which of the following parameter can be neglected for a short line? Capacitance
38. The under voltage relay can be used for generators busbars transformers motors
39. In order that current should flow without causing excessive heating or voltage drop, the relay
contacts should
Have low contact resistance , Be clean and smooth, Be of sufficient size and proper shape
40. On which of the following effects of electric current a fuse operates? Heating effect
Oil circuit breakers, Air blast circuit breakers, Minimum oil circuit breakers
45. Relays are used for phase faults on long line. Impedence.
46. By which of the following methods major portion of the heat generated in a H.R.C. fuse
is dissipated ? Conduction
the spring tension, the rate of flux built up, armature core air gap
48. If the fault occurs near the impedance relay, the VII ratio will be
49. Oil switches are employed for High v And Large current
50. Which of the following circuit breakers has high reliability and minimum maintenance ?
SF6
51. For which of the following ratings of the transformer differential protection is
recommended ? Equal to Abouve 2 Mva
52. When a wave propagates on a transmission line, it suffers reflection several times at
57. Which of the following is the least expensive protection for overcurrent is low voltage
system ? Rewireable fuse
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)
14. Recovery voltage is the value of the r.m.s. voltage that re-appears across the
poles of a
circuit breaker before
a) Restriking voltage
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)
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. Overload
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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
Answer.2. Instantaneous
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
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.1. Power
SHAHAJIRAO PATIL VIKAS PRATISHTHAN
S. B. PATIL COLLEGE OF ENGINEERING, INDAPUR, DIST: PUNE.
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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
4. None of the above
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.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
4. None of the above
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
4. None of the above
Answer.4. Short-circuits
Ques.40. The ground wire should not be smaller than No ______ copper.
1. 2
2. 4
3. 6
4. 10
Answer.4. 10
SHAHAJIRAO PATIL VIKAS PRATISHTHAN
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DEPARTMENT OF ELCTRICAL ENGINEERING
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.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.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
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.55. Discrimination between main and back up protection is provided by the use of
relays
1. Facts
2. Sensitive
3. Slow
4. None of the above
Answer.3. Slow
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
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
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.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
4. None of the above
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.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. 16
2. 12
3. 4
4. 8
Answer.4. 8
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DEPARTMENT OF ELCTRICAL ENGINEERING
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
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.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
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
4. None of the above
Answer.1. Zero
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
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
4. None of the above
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
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.1. Current
Answer.1. DC
Answer.3. Isolator
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
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.
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
SHAHAJIRAO PATIL VIKAS PRATISHTHAN
S. B. PATIL COLLEGE OF ENGINEERING, INDAPUR, DIST: PUNE.
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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
Ques.106. Which among these circuit breakers produce the least arc energy?
a. Plain oil
b. Minimum oil
c. Air blast
d. Air break
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
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.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
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
SHAHAJIRAO PATIL VIKAS PRATISHTHAN
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DEPARTMENT OF ELCTRICAL ENGINEERING
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
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.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
SHAHAJIRAO PATIL VIKAS PRATISHTHAN
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DEPARTMENT OF ELCTRICAL ENGINEERING
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.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
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
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
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
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
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
D. None of the above
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
D. None of the above
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
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.143. In carrier current protection the purpose of the wave trap is for
SHAHAJIRAO PATIL VIKAS PRATISHTHAN
S. B. PATIL COLLEGE OF ENGINEERING, INDAPUR, DIST: PUNE.
DEPARTMENT OF ELCTRICAL ENGINEERING
ANSWER: Trapping high frequency waves entering into generators/ transformer unit
Ques.146. Requirements of protection power station buildings against direct strokes are
A. Interception
B. Conduction
C.. Dissipation
D. All of the above
ANSWER: All of the above
Ques.147.The protection against direct lighting strokes and a high-voltage steep waves is
provided by
A. Ground wires
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B. Lightning arresters
C. Lightning arresters and ground wires
D. Earthling of neutral
ANSWER: Lightning arresters and ground wires
ANSWER: 66 KV
A. Switchgears
B. Substations
C. Intermediate substations
D. Transformation stations
ANSWER: Sub-stations
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)
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)
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)
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)
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 to 0.6
d) 0.6 to 1.0
Ans:
a) Impedance
b) Current difference
c) Voltage difference
d) None of these
Ans:
a) Stability, reliability
b) Speed sensitivity
c) Selectivity, adequacy
d) None of these
Ans:
6. Protective relays are devices which detect abnormal conditions in electrical circuit by
measuring___________.
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:
a) Current difference
b) Voltage difference
c) Impedance difference
d) Distance between two CT’s
Ans:
a) Line-to-line fault
b) Line-to-line circuit
c) Dead short circuit
d) Both (a) and (b) occurring simultaneously
Ans:
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:
a) 5 to 10 kg/cm2
b) 10 to 15 kg/cm2
c) 15 to 20 kg/cm2
d) 20 to 30 kg/cm2
Ans:
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) Both (a) and (b) above
Ans:
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) Both (b) and (c)
Ans:
a) Induction type
b) Shaded pole type
c) Thermocouple type
d) Permanent magnet moving coil type
Ans:
a) Polarized type
b) Balance beam type
c) Hinged armature type
d) Induction disc type
Ans:
a) Voltage polarities
b) Flow of current
c) Flow of power
d) All of these
Ans:
a) Thermal emission
b) Alternators
c) Field emission
d) Transmission lines
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:
Ans:
23. The voltage across the circuit breaker pole after final current zero is__________.
a) Restriking voltage
b) Supply voltage
c) Recovery voltage
d) None of these
Ans:
24. Which of the following circuit breakers takes minimum time installation?
Ans:
25. In a power system, the rate of rise of Restriking voltage depends upon__________.
Ans:
26. In a circuit breaker, the arcing contents are made of__________.
a) Aluminum
b) Electrolytic
c) Copper tungsten alloy
d) Tungsten
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__________.
Ans:
a) Thermal emission
b) Alternators
c) Field emission
d) Transmission lines
Ans:
a) 4 kV
b) 25 kV
c) 10 kV
d) 36 kV
Ans:
31. Circuit breakers are essentially__________.
Ans:
32. The voltage across the circuit breaker pole after final current zero is__________.
a) Restriking voltage
b) Supply voltage
c) Recovery voltage
d) None of these
Ans:
33. Which of the following circuit breakers takes minimum time installation?
Ans:
34. In a power system, the rate of rise of Restriking voltage depends upon__________.
Ans:
a) Aluminum
b) Electrolytic
c) Copper tungsten alloy
d) Tungsten
Ans:
36. Fault diverters are basically__________.
a) Circuit breakers
b) Fast switches
c) Relays
d) Fuses
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__________.
Ans:
a) Instantaneous relays
b) Definite time lag
c) Inverse time lag
d) All of these
Ans:
Ans:
41. In carrier current protection, wave trap is used is for trapping__________.
Ans:
a) A.C. only
b) D.C. only
c) Both (a) and (b)
d) None of these
Ans:
a) MHO relays
b) Reactance relays
c) Impedance relays
d) All of these
Ans:
Ans:
a) Overhead lines
b) Transformer
c) Motors
d) Cables
Ans:
46. Under voltage relays are used for__________.
a) Motors
b) Alternators
c) Bus bars
d) All of these
Ans
a) Earth faults
b) Interphase faults
c) Both (a) and (b)
d) None of these
Ans:
a) Transformer
b) Alternator
c) Overhead lines
d) C.T., P.T.
Ans:
Ans:
a) Inter-turn faults
b) Heavy Loads
c) External Faults
d) Magnetizing current
Ans:
51. Back up protection is needed for__________.
a) Over voltage
b) Short circuits
c) Over current
d) All of these
Ans:
Ans:
a) In three zones
b) In two zones
c) Independent of zone
d) None of these
Ans:
a) Current
b) Power
c) Voltage
d) Impedance
Ans:
Ans:
56. A relay is used to__________.
Ans:
Ans:
a) Transformer
b) Overhead line equipment
c) Alternator
d) Motors
Ans:
a) Air gap
b) Back up stop
c) Number of ampere turns
d) All of these
Ans:
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) Every internal fault
Ans:
a) 0.0001 sec
b) 0.001 sec
c) 0.01 sec
d) 0.1 sec
Ans:
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) Relay
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-lines
Ans:
a) SCR
b) Thyristors
c) UJT
d) None of these
Ans:
Ans:
a) In three zones
b) In two zones
c) Independent of zone
d) None of these
Ans:
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:
a) Impedance
b) Current difference
c) Voltage difference
d) None of these
Ans:
a) Stability, reliability
b) Speed sensitivity
c) Selectivity, adequacy
d) None of these
Ans:
74. Protective relays are devices which detect abnormal conditions in electrical circuit by
measuring__________.
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:
a) Line-to-line fault
b) Line-to-line circuit
c) Dead short circuit
d) Both (a) and (b) occurring simultaneously
Ans:
a) Equal to zero
b) Less than now
c) Equal to one
d) More than one
Ans:
Ans:
a) Increase
b) Reduce
c) Remain same
d) May increase or decrease
Ans:
81. Fusing factor is defined as the ratio between__________.
Ans
a) 25 A
b) 50 A
c) 75 A
d) 100 A
Ans:
Ans:
Ans
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:
Ans:
Ans:
a) Trip Coil
b) Contacts
c) Handle
d) Medium
Ans:
a) Manually
b) Automatically
c) That it should give warning
d) None of these
Ans:
91. Arcing time is the time between__________.
Ans:
92. 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) 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) None of these
Ans:
94. In circuit breaker, to facilitate arc quenching, dielectric strength can be increased
by__________.
Ans:
Ans:
Ans:
Ans:
a) Restriking voltage
b) Rate of rise Restriking voltage
c) Power factor
d) Frequency
Ans:
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__________.
a) Restriking voltage
b) Final arc distinction
c) Rise of voltage
d) All of these
Ans:
Ans:
a) Decrease in voltage
b) Increase in voltage
c) Pressure of arc
d) Mechanical stresses
Ans:
a) Short duty
b) Intermittent duty
c) Repeated duty
d) All of these
Ans:
a) Breaking capacity
b) Making capacity
c) Short time capacity
d) All of these
Ans:
a) Zero voltage
b) Zero current
c) High current
d) High voltage
Ans:
Ans:
Ans:
a) High
b) Low
c) Medium
d) None of these
Ans:
a) Is easily inflammable
b) May from an explosive mixture with air
c) Requires maintenance
d) All of these
Ans:
Ans:
111.Current copping tendency is minimized by using the F6 gas at relatively__________.
Ans:
Ans
Ans:
Ans:
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:
Ans:
118. Where voltages are high and current to be interrupted is low the breaker preferred
is__________.
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) Carrier protection.
b) Transformer protection.
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__________.
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) 4 s
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) 15 A
Ans:
127. In an inverse definite minimum time electromagnetic type over current relay, the
minimum time feature is achieved because of_________.
Ans:
a) Impedance
b) Reactance,
c) Mho.
d) All of the above
Ans:
Ans:
130. Threshold characteristics of a plain impedance relay in a complex Z plane is a_______.
Ans:
a) Non-directional relay.
b) Directional relay.
c) Differential relay.
d) None of these.
Ans:
Ans:
133. The relay best suited for phase fault relaying for medium transmission line
is__________.
a) MHO relay.
b) Reactance relay.
c) Impedance relay. d) None of these.
Ans:
135. For the protection of lines against faults involving variable fault resistance, the
preferred relaying scheme is__________.
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 relay.
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 relay.
c) Reactance relay.
d) Induction relay.
Ans:
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__________.
Ans:
a) Induction relay.
b) Thermal relay.
c) Impedance relay.
d) MHO relay.
Ans:
Ans:
a) Feeders.
b) Alternators
c) Transformers.
d) All of these.
Ans:
144. Both voltage and current signals are required for__________.
Ans:
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__________.
Ans:
a) Transformer
b) Transmission line
c) Motors
d) Generators
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__________.
Ans:
150. Over conventional electromechanical relays, the transistor relay has the limitations of
__________.
Ans:
151. In a static overload relay, inverse time characteristics are obtained by__________.
a) A transistor amplifier
b) An integrating circuit
c) A transistor switch.
d) A differentiating circuit
Ans:
a) Phase comparison
b) Amplitude comparison
c) Starting an impedance relay
d) Biasing a MHO relay
Ans:
a) Transformer amplifier
b) Transistor logic circuit
c) Rectifier bridge
d) Thyristor Bridge
Ans:
Ans:
155. The phase comparators in case of a static relays and electromechanical relays normally
are__________.
Ans:
a) Distance protection
b) Differential protection
c) Both (a) & (b)
d) Neither (a) nor (b)
Ans:
a) alternators.
b) transformers.
c) transmission lines.
d) both (a) and (b).
Ans:
a) motor protection,
b) capacitor protection.
c) rectifier protection.
d) generator protection.
Ans:
a) circuit breakers.
b) transformers.
c) CTs.
d) PTs.
Ans:
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__________.
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) Synchronous reactance
d) None of the above
Ans:
163. 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.
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) Merz-Price protection.
c) Buchholz protection.
d) None of the above.
Ans:
a) Thermal relays.
b) Over-current relays.
c) Thermal sensitive relays.
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 __________.
Ans:
Ans:
169. For the protection of a large squirrel cage induction motor against single phasing
normally__________.
Ans:
170. The main function of under voltage protective device generally employed with a motor starter
is to__________.
Ans:
a) Stator.
b) Rotor.
c) Over-load.
d) Under-voltage.
e) Unbalanced supply voltages and reverse or open phase starting.
f) All of the above.
Ans:
172. Earth fault protection for an electric motor is provided by means of__________.
Ans:
173. The relay used for protection of power transformers against internal faults is __________.
a) Buchholz relay
b) MHO relay
c) Induction relay
d) Impedance relay
Ans:
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 connection
d) Δ –Y connection
Ans:
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) 1: 23
b) 23:1
c) 23: √3
d) √3:23
Ans:
Ans:
178. The percentage differential protection of a transformer protects the transformer against
__________.
a) External faults
b) Magnetizing current inrush
c) Overloading
d) Internal fault
Ans:
Ans:
Ans:
181. For the protection of transformer harmonic restraint is used to guard against__________.
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 phase
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) The relay restraining coil is biased with the second harmonic current.
b) Time lag is provided in the relay.
c) Relay sensitivity is reduced by employing shunt.
d) All of the above.
Ans:
Ans:
185. ____________ protection used for protection of transmission line is a unit type
protection.
a) Distance
b) Current graded over-current
c) Carrier current
d) Time graded over-current
Ans:
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:
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__________.
Ans:
191. Adjustable resistors are connected in the pilot wires in order to__________.
Ans:
192. 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.
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________.
Ans:
194. Carrier current protection scheme is normally used for protection of HV cables only
________.
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:
Ans:
Ans:
198. In an overhead transmission line, wave traps are used for the detection of__________.
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__________.
Ans:
Ans:
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) Line trap has low impedance to 50HZ signal but high impedance to carrier current
signal, where as a coupling capacitor has high impedance to 50 Hz signal but low
impedance to carrier signal.
(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% of the first line, 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 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% of its full-length.
Ans:
206. 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.
Ans:
207. In distance protection of transmission line, the voltage at the relay point ________ with
increase of distance of fault point from the relay.
a) Increases
b) Decreases
c) Remains constant
d) Drops to zero instantaneously
Ans:
d) All of above
Ans:
a) arcing to core
Ans:
a) lightning
b) resonance
c) switching
d) all of these
Ans:
SGP MCQS QUESTION BANK
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:B
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
High Current
ANSWER:B
ANSWER :B
12)In which relay having no effect on arc fault-
Impedance
reactance
MHO
Thermal overlod
ANSWER : B
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
ANSWER : B
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
SGP MCQS QUESTION BANK
22) The earth fault protection of short and medium lines is used-
Quadrilateral relay
Electro magnetic
Electro mechanical
none
ANSWER : A
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.
SGP MCQS QUESTION BANK
25) It is a technology to improve situation and visibility within power system grids
is
WAM
PMU
PLCC
None
ANSWER : A
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
None
ANSWER: A
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
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:C
41) 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
ANSWER:C -MVA
SGP MCQS QUESTION BANK
43) In impedance relay, current element torque should be-
Equal to voltage element torque
None of these
ANSWER:B
ANSWER:C
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
SGP MCQS QUESTION BANK
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
ANSWER : B
ANSWER : A
50)The measurement of electrical quantity is done by-
Stationary network
Moving N/W
Zig Zag
All of Above
ANSWER : A
ANSWER : A
52) 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
ANSWER : B
54) The low pass filter which filter out undesired frequency component is
Alliasing Filter
Aniti-aliasing Filter
PMU
SGP MCQS QUESTION BANK
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
ANSWER : C
ANSWER : C
59) The diff.protection is based in current circlation principle is known as-
Bias Protection
SGP MCQS QUESTION BANK
% 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
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
ANSWER : D
65) For mesured of overheat ,tempreture sensor embeded with whatstones bridge
principle are use-
Thermal Overload realy
RTD
Induction type
Impedance type
ANSWER : B
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
2 Tesla
3Tesla
2.5 Tesla
ANSWER : B
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
SGP MCQS QUESTION BANK
D.Unity
ANSWER : B
ANSWER : B
A.Brushes
B.Poles
C.Armature
ANSWER : B
A.50 Hz
B.60 Hz
ANSWER : A
75)An alternator coupled to which primemover will usually have the highest rotating speed
A.Steam engine
D.Steam turbine
ANSWER : D
C.Frequency of waveform
ANSWER : D
ANSWER : C
A.0.2% to 0.5%
B.2% to 5%
C.12% to 15%
D.20% to 30%
ANSWER : B
SGP MCQS QUESTION BANK
80)Star/star transformers work satisfactorily when........
ANSWER : B
ANSWER : D
82)Which of the following inductor will have the least eddy current losses?
A. Air core
C. 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
SGP MCQS QUESTION BANK
B.Field winding
ANSWER : C
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
SGP MCQS QUESTION BANK
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
A 20 KV to 100 KV
B Upto 20 KV
C Above 100 KV
D 60 KV to 80 K
ANSWER : C
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
SGP MCQS QUESTION BANK
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
SGP MCQS QUESTION BANK
ANSWER : A
C. Switching resistance in relay restrain circuit at pre-set time interval by means of a timer
element
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
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
A. Thermal
B. Electromagnetic
C. Induction
ANSWER : D
D. Either A or B
ANSWER : D
A. Under reaches
B. Over reaches
C. Reach unaffected
ANSWER : A
ANSWER : B
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
SGP MCQS QUESTION BANK
ANSWER : D
A. Nondirectional relay
B. Directional relay
C. Differential relay
ANSWER : B
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
SGP MCQS QUESTION BANK
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
ANSWER : A
110) In order that current should flow without causing excessive heating or voltage drop, the
relay contacts should
SGP MCQS QUESTION BANK
A. Have low contact resistance
ANSWER : D
SWITCHGEAR & PROTECTION Multiple Choice Questions :-
Ans: d
Ans: d
3. SF6 gas
(c) is nontoxic
Ans: c
(b) porcelain
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 ?
Ans: c
(a) fuses
(b) relays
Ans: c
(a) short-circuit
(b) temperature
(c) overload
Ans: c
Ans: d
Ans: a
SWITCHGEAR & PROTECTION Objective Questions
(d) temperature
Ans: e
(a) induction
(c) thermal
(d) electromagnetic
Ans: e
13. Thermal overload relays are used to protect the motor against over current due to
(a) short-circuits
(c) grounds
(d) all of the above
Ans: b
(a) delayed
(b) instantaneous
Ans: b
Ans: c
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
Ans: d
Ans: a
Ans: a
20. The current zero interruption, in oil and air blast circuit breakers, is achieved by
Ans: c
Ans: d
Ans: d
(a) power
(b) current
Ans: a
Ans: c
Ans: d
Ans: a
Ans: c
29. Protective relays are devices that detect abnormal conditions in electrical circuits by measuring
(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
(e) none of the above
Ans: a
Ans: d
Ans: c
Ans: d
Ans: d
Ans: a
Ans: a
Ans: a
Ans: c
(a) overload
(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
Ans: a
42. Which of the following is the least expensive protection for overcurrent is low voltage system ?
(b) Isolator
Ans: a
(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
Ans: c
(a) SFe
Ans:
46. To protect most of the electrical equipment handling low power, the types of relays used are
(a) thermocouple
Ans: c
Ans: b
48. Ungrounded neutral transmission system is not recommended because of system
(b) insulation overstress may lead to failure and subsequent phase to phase faults
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
Ans: c
51. The line insulation is the insulation level of the station equipment.
(b) same as
(c) more than
(d) proportional to
Ans: e
52. The interaction between a transmission line and communication line is minimized by
Ans: d
53. When a wave propagates on a transmission line, it suffers reflection several times at
(a) tapping
Ans: d
(c) An impedance relay has maximum fault current when fault occurs near the relay
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
(a) current
(b) voltage
(c) impedance
Ans: d
Ans: d
(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
Ans: e
(a) reactors
(b) resistors
(c) capacitors
Ans: a
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
Ans: d
(a) Impedance
(b) Reactance
Ans: a
65. For which of the following protection from negative sequence currents is provided ?
(a) Generators
(b) Motors
(d) Transformers
Ans: a
(b) Reactance
(c) Impedance
Ans: b
Ans: d
68. For which of the following ratings of the transformer differential protection is recommended ?
69. A _______ is used to measure the stator % winding temperature of the generator.
(a) thermocouple
(b) pyrometer
(d) thermometer
Ans: c
(a) generators
(b) busbars
(c) transformers
(d) motors
Ans: e
71. The relay with inverse time characteristic will operate within
(b) 5 to 10 sec
(c) 5 to 20 sec
(d) 20 to 30 sec
Ans: b
72. The single phasing relays are used for the protection of
Ans: d
73. Which of the following devices will receive voltage surge first travelling on the transmission line ?
(b) Relays
(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
Ans: a
76. Which of the following circuit breakers has high reliability and minimum maintenance ?
Ans: b
Ans: a
(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
Ans: b
Ans: d
82. Air blast circuit breakers for 400 kV power system are designed to operate in
(b) 50 millisecond
Ans: b
Ans: b
Ans: a
(a) impedance
(b) directional
(c) non-directional
Ans: b
Ans: a
87. If the fault occurs near the impedance relay, the VII ratio will be
(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
Ans: b
89. The steady state stability of the power system can be increased by
Ans: a
90. The inductive interference between power and communication line can be minimized by
Ans: c
(b) motor
(c) generator
(d) feeder
Ans: a
Ans: a
Ans: d
(a) current
(b) voltage
(c) VAR
(d) kVA
Ans: a
(a) burning
(b) arcing
(c) melting
Ans: c
Ans: d
(a) overload
Ans: b
(a) 20 A
(b) 50 A
(c) 100 A
(d) 200 A
Ans: c
Ans: a
Ans: c
(d) switching, controlling and protecting the electrical circuit and equipment
Ans: d
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
Ans: c
Ans: b
106. The information to the circuit breaker under fault conditions is provided by
(a) relay
Ans: a
(b) isolators
(c) H.R.C. fuses
(d) reactors
Ans: d
Ans: b
110. In a single bus-bar system there will be complete shut down when
Ans: a