Switchgear and protection mcq - electrical engineering Multiple Choice Questions - Electrical input

Sunday, August 5, 2018

Switchgear and protection mcq - electrical engineering Multiple Choice Questions

                                       Switchgear and protection mcq

important switchgear and protection mcq (electrical engineering mcq)---

1. SF6 gas ---------
(a) has pungent small
(b) is nontoxic
(c) is lighter than air
(d) is yellow in colour
 (e) all of the above
Ans:- b

2. The main function of a fuse -----
(a) protect the appliance
(b) prevent excessive currents
(c) open the circuit
(d) protect the line
(e) none of the above
Ans:- b

3. Which of the following medium is employed for extinction of arc in air circuit breaker
(a) Mineral Oil
(b) Air
(c) SF6
(d) Water
Ans:-  b

4.  The arcing contacts in a circuit breaker are made of
(a) Aluminium alloy
(b) copper tungsten alloy
(c) Magnine
(d) Nichrom
Ans:- b

5.With which of the following, a circuit breaker must be equipped for remote operation----
(a) Time-delay trip
(b) Shunt trip
(c) Inverse time trip
(d) all of the above
(e) none of the above
Ans:-- b

6. Fault diverters are basically ----
(a) Relays
(b) fast switches
(c) contactors
(d) SF6 circuit breakers
Ans:- b

  7. Arc in a circuit behaves as ---

(a) inductive reactance
(b) capactive reactance
(c) a resistance decreasing with voltage rise across the arc
(d) resistance increasing with voltage rise across the arc
Ans:- c

  8. Relays can be designed to respond to changes in
(a)  voltage and current
(b) resistance, reactance or impedance
(c) light intensity
(d) temperature
(e) all of the above
Ans:-- e

9.  A thermal protection switch can protect against -----
(a) short-circuit
(b) temperature
(c) overload current
(d) over voltage
 (e) none of the above

Ans:- write in comment box

10. 10. Thermal circuit breaker has à
(a) instantaneous trip action
(b) delayed trip action
(c) both  (a) and (b)
(d) none of the above

 11. Overload relays are of ……. type.
(a) electromagnetic
(b) solid state
(c) thermal
(d)  induction
(e) all of the above
Ans: e

12. Thermal overload relays are used to protect the motor against over current due to
(a) ground
(b) heavy loads
(c) short-circuits
(d) none of the above
Ans:--  b

13. 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

14. In order that current should flow without causing excessive heating or voltage drop, the relay contacts should :---
(a)  be of sufficient size and proper shape
(b) be clean and smooth
(c) have low contact resistance
(d)  all of the above properties
Ans:--- d

15. 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:--- d

16. An efficient arid a well designed protective relaying should have
(a) good selectivity and reliability
(b) high speed and selectivity
© - economy and simplicity
(d) all of the above
Ans:-- d

17. A differential relay measures the vector difference between
(a)  two voltages
(b) two currents
(c) two or more similar electrical quantities
(d) all of the above
Ans:-- c

18. Burden of a protective relay is the power
(a) developed by the relay circuit
(b)  required to operate the circuit breaker
(C)  absorbed by the circuit of relay
(d) all of the above

19. Directional relays are based on flow of ---
(a) voltage
(b) current
(c) power
(d) none  of the above
Ans:à C

20. 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

21. Shunt capacitance is neglected while considering ->
(a) Long transmission line
(b) medium transmission line
 (c)  short transmission line
(d) medium and long transmission lines

22. Overheating of relay contacts or contact born out is due to -->
(a)  too low contact pressure
(b) foreign matter on the contact surface
(c)  slow making and breaking of load circuit contacts
(d) all of the above
Ans:- d

23. In a circuit breaker the basic problem is to à
(a) emit the ionizing electrons
(b) maintain the arc
(c) extinguish the arc
(d) transmit large power
Ans: --d

24. H.R.C. fuses provide best protection against
(a) short-circuits
(b) reverse current
(C) short-circuits
(d) overload

25. The ground wire should not be smaller than No _______ copper.
(a) 7
(b) 8
(c) 9
(d) 10
Ans:--- d

26. insulation resistance of high voltage circuit breakers is more than
(a) 10 mega ohms
(b) 50 mega ohms
(c) 70 mega ohms
(d) 100 mega ohms
Ans:- d

27. The time of closing the cycle, in modern circuit breakers is
(a) 0.001 sec
(b) 0.003 sec
(c) 0.010 sec
(d) 0.10 sec
(e) none of the above

28. The delay fuses  are  used  for  the protection of à
(a)  light circuits
(b) fluorescent lamps
(c) power outlet circuits
(d) motors

29. Resistance grounding is used for voltage between
(a) 11V to 33kV
(b) 3.3kV to 11kV
(c)  33kVto66kV
(d) none of the above
Ans: - write ans in comment box

30. The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to _->
(a) extinguish the arc
(b) insulate the contacts from switch body
(c) lubricate the contacts
(d) none of the above
(e) all of the above
Ans:-- a

31. undergrounded 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

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

 33. For the protection of power station buildings against direct strokes the requirements are
(a)   interception and conduction
(b)  interception
(c)  interception, conduction and dissipation
(d)  interception, conduction, dissipation and reflection
(e)  all of the above
Ans:-- c

34. The interaction between a transmission line and communication line is minimized by
(a) increasing the height of the trans-mission line tower
(b) transposing transmission as well as communication lines
(c)  increasing the distance between the two lines
(d) All of the above
Ans:-- d

35. Discrimination between main and back up protection is provided by the use of relays which are
(a) slow
(b) fast
(c) sensitive
(d) none of the above
Ans:- a

36. When a wave propagates on a transmission line, it suffers  reflection several times at
(a) sending end
(b) load end
(c) tapping
(d) sending and receiving end
(e) all of the above
Ans: d

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

38. Which of the following statements is incorrect-->
(a) Shunt reactors are used as compensation reactors
(b) Lightning arrestors are used before the switchgear
(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

39. A.C. network analyser is used to solve problems of
(a) load flow
(b)  load flow, short-circuit and stability
 (c)  load flow and stability
(d) load flow and short-circuit
(e) none of the above

40. To reduce short circuit fault currents are used
(a) capacitors
(b) reactors
(c) resistors
(d) none of the above
Ans:-- a

41. For cost and safety, the outdoor substations are installed for voltages above
(a) 11 kV
(b) 33 kV
(c) 66 kV
(d) 132 kv
Ans:- b

42. relays are used for phase faults on long line.
(a) Reactance
(b) impedance
(c) both (a) and (b)
(d) None of the above
Ans:-- b

43. For which of the following protection from negative sequence currents is provided
(a) Transformer
(b) Motors
(c) Transmission line
(d)  Generator
  Ans--> d

44. Distance relays are generally--
(a)   impedance relays
(b)  reactance relays
(c)  split-phase relays
(d) none of the above

Ans:- d

45. which of these  used to measure the stator % winding temperature of the generator.
(a) thermocouple
(b) pyrometer
(c) thermometer
(d) resistance thermometer
Ans:- d
46. . The single phasing relays are used for the protection of
(a) two phase motors only
(b) two single phase motors running in parallel
(c)  three phase motors
(d) single phase motors only
Ans:- c

47. Series reactors must have --
(a) low resistance
(b) high reatance
(c) low impedance
(d) high impedance
Ans:- a

48.  Which of the following circuit breakers has high reliability and minimum maintenance
(a) Oil circuit breakers
(b) Vacuum circuit breakers
(c )  Circuit breaker with SF6 gas
(d) Air blast circuit breakers
 Ans:- c

49.  Arc in a circuit breaker is interrupted at à
(a) zero current
(b) maximum current
(c) minimum voltage
(d) maximum voltage
Ans:-- a

50. Series capacitors are used to à
(a) compensate for line capacitive reactance
(b) compensate for line inductive reactance
(c) improve line current
(d) none of the above
Ans:- b

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