1. A thermal protection switch provides protection against what? (a)
a. Overload
b. Temperature
c. Short circuit
d. Overvoltage
Ans: a
2. 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 an explosive mixture with air.
c. Possibility of causing fire hazards.
d. All of the above.
Ans: d
3. 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
Ans: a
4. Which circuit breaker is preferred to be installed in extra high
voltage AC system?
a. Bulk oil type circuit breaker
b. Air blast circuit breaker
c. SF6 circuit breaker
d. Vacuum circuit breaker
Ans: c
5. Which of the following materials can be used as an arc quenching
medium in high Rupturing Capacity (HRC) fuse?
a) Aluminium
b)Argon gas
c) Mica
d) Plaster of paris
Ans: d
6. The phenomenon of current chopping mainly occurs in which type of circuit breaker?
a) Oil circuit breaker
b)Air blast circuit breaker
c) SF6 circuit breaker
d)Vaccum circuit breaker
Ans: b
7. The arrangement given is of protection of alternator against
a)Turn-turn fault in any single stator winding
b)Insulation failure of the stator winding
c)Unbalancing loading
d)Earth fault
Ans: c
8. SF6 gas
a)Is yellow in colour
b)Is lighter than air
c)Is nontoxic
d)Has pugment smell
Ans: c
9. Arc in a circuit behave as
a. A capacitive 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. 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
Ans: d
11. For which among the following the current ratings are not required?
a. Circuit breakers
b. Relays
c. Isolators
d. Load break switch
Ans: c
12.Protective relays can be designed to respond to ___________.
a. Light intensity, impedance
b. Temperature, resistance, reactance
c. Voltage and current
d. All of these
Ans: d
13. 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
Ans: d
14. Plug setting of an electromagnetic relay can be altered by varying
a. Number of ampere turns
b. Air gap of magnetic path
c. Adjustable back stop
d. None of these
Ans: a
15. 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
Ans: b
16. The arcing contacts in a circuit breaker are made of
(a) copper tungsten alloy
(b) porcelain
(c) electrolytic copper
(d) aluminium alloy
Ans: a
17.Air blast circuit breaker is used for
(a) over currents
(b) short duty
(c) intermittant duty
(d) repeated duty
Ans: d
18. The current zero interruption, in oil and air blast circuit breakers, is
achieved by
(a) lengthening of the gap
(b) cooling and blast effect
(c) both (a) and (b)
(d) deionizing the oil with forced air
Ans: c
19. Directional relays are based on flow of
(a) power
(b) current
(c) voltage wave
(d) all of the above
Ans: a
20. 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
21.A transmission line is protected by
(a) inrush protection
(b) distance protection
(c) time graded and current graded over current protection
(d) both (b) and (c)
Ans: d
22. 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
23.The voltage appearing across the contacts after the opening of the circuit breaker is called______voltage.
(a) recovery
(b) surge
(c) operating
(d) arc
Ans: a
24. 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
25. The time of closing the cycle, in modern circuit breakers is
(a) 0.003 sec
(b) 0.001 sec
(c) 0.01 sec
(d) 0.10 sec
Ans: a
26.H.R.C. fuses provide the best protection against
(a) overload
(b) reverse current
(c) open-circuits
(d) short-circuits
Ans: d
27. Resistance grounding is used for voltage between
(a) 33kVto66kV
(b) HkVto33kV
(c) 3.3kVandllkV
(d) none of the above
Ans: c
28. 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
Ans: c
29. 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
30. Circuit breakers usually operate under
a) Steady short circuit current
b) Sub transient state of short circuit current
c) Transient state of short circuit current
d) None of these
Ans: c
31.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 transmission line tower
(c) increasing the distance between the two lines
(d) all of the above
Ans: d
32. 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
33. Induction cup relay is operated due to changes in
(a) current
(b) voltage
(c) impedance
(d) all of the above
Ans: d
34. 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
35.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
36. 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
37. Why is the resistance switching used in an air blast circuit breaker?
a. Reduce the magnitude of fault current.
b. Control the CB operating time.
c. Damp out the fast transient.
d. Change the fault current power factor.
Ans: c
38. A Buchholz relay is used for:
a) Protection of a transformer against all internal faults
b) Protection of a transformer against external faults
c) Protection of a transformer against both internal and external faults
d) Protection of induction motors
Ans: a
39. Mho relay is usually employed for the protection of
a) Short line only
b)Medium lines only
c) Long lines only
d)Any line
Ans: c
40.Recovery voltage is the value of RMS voltage that reappears across the poles of a circuit breaker before_______________
a. Restriking voltage
b. Final arc extinction
c. Rise of voltage
d. All of the above
Ans: b
41.The making and breaking currents of a 3 phase ac circuit breakers in power systems are respectively in ________form.
a. rms value, rms value
b. Peak Value, rms value
c. rms value, instantaneous value
d. instantaneous value, instantaneous value
Ans: b
42. What is restriking voltage?
a. The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction.
b. The transient voltage that appears across the circuit breaker contacts at the end of arc extinction.
c. Both (a) and (b)
d. None of the above
Ans: a
43.Power station and sub-stations are protected against direct strokes of lightning using
a) Rod gap arrester
b)Overhead ground wires
c) Earthing screen
d)Horn gap arrester
Ans: c
44. In Busbar protection what is method of providing an earthed metal barrier surrounding a Busbar throughout its length called?
a)Fault bus protection
b)Distance protection
c)Differential protection
d)Time graded over current protection
Ans: a
45.Solid-state power supplies are protected from high voltage surges
due to lightning using:
a) Metal glaze resistors
b) Silicon-carbide varistor
c) Zinc-oxide-based varistor
d)Metal film resistors
Ans: b
46. Arc in a circuit breaker is interrupted at
a) Minimum voltage
b)Maximum current
c) Zero current
d)Maximum voltage
Ans: c
47.Keeping in view the cost and the overall effectiveness, which of the following circuit breaker is best suited for capacitor bank switching?
a. Vacuum circuit breaker
b. Air blast CB
c. SF6
d. Oil CB
Ans: a
48.The relay used for feeder protection
a) Undervoltage relay
b) Translay relay
c) Thermal relay
d) Buchholz relay
Ans: b
49.A distance relay is said to be inherently directional if its characteristic
on R-X diagram:
a) Is a straight line offset from origin
b)Is a circle that passes through origin
c) Is a circle that encloses origin
d)Is a straight line passes through origin
Ans: b
50.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
51. To limit current chopping in vacuum circuit breakers, the contact material employed should have the properties of (A)
a. Low conductivity and high vapour pressure.
b. Low conductivity and low vapour pressure.
c. High conductivity and high vapour pressure.
d. High conductivity and low vapour pressure.
Ans: a
52.Match List-I ( Type of relays) with List-II ( Protective schemes) and select the correct
answer
List-I
A) Negative-sequence relay
B) Harmonic-restraint differential relay
C) Over-current relay with time-delay
D) Mho relay
LIST-II
- Distribution feeder protection
- Long h.t line protection
- Transformer protection
- Rotor protection alternators
Codes:
A B C D
a) 4 3 1 2
b) 1 2 4 3
c) 4 2 1 3
d) 1 3 4 2
Ans: a
53. The interrupting time of a circuit breaker is the period between the instant of _________.
a. Initiation of short circuit and the arc extinction on an opening operation.
b. Energizing the trip circuit and the arc extension on an opening operation.
c. Initiation of short circuit and the parting of primary arc contacts.
d. Energizing of the trip circuit and the parting of primary arc contacts.
Ans: b
“Take risks in your life. If you win, you can lead, if you lose, you can guide“
-Swami Vivekananda
For detail explanation of each question you can watch this video..
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