Circuit Breakers MCQs

31. The making current of 3-phase breaker with rating 2000 MVA, 33 kV will be

  1. 35 A
  2. 50 A
  3. 70 kA
  4. 89 A

Answer. d

32. An air blast circuit breaker is usually employed for

  1. Instantaneous voltage
  2. Intermittent duty
  3. Repeated duty
  4. Short duty

Answer. c

33. The recovery voltage that appears across the circuit breaker contacts will be maximum for power factor of

  1. Zero
  2. 0.5
  3. 0.707
  4. Unity

Answer. a

34. Air used in air blast circuit breaker must

  1. Be free from moisture
  2. Have least CO2
  3. Be ionized
  4. Have oil mist

Answer. a

35. Breaking capacity of a circuit breaker is usually expressed in

  1. Volts
  2. Amperes
  3. MVA
  4. MW

Answer. c

36. In the event of a fault on the connected circuit, a circuit breaker will operate

  1. Automatically
  2. Manually
  3. Manually through a control switch
  4. Depending on the design

Answer. a

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

  1. Operating mechanism
  2. Conservator
  3. Explosion pot
  4. Fixed and moving contacts

Answer. b

38. In a circuit breaker, ionization is not facilitated by

  1. Material of contacts
  2. Increase of mean path
  3. Increase of field strength
  4. High temperature of surrounding medium

Answer. a

39. At electric breakdown

  1. Conductor become insulator
  2. Insulator becomes conductor
  3. Semiconductor becomes conductor
  4. Conductor becomes superconductor

Answer. b

40. In the case of circuit breakers if the length of arc increases, its resistance is

  1. Decreases
  2. Increases
  3. Remain same
  4. Some times increases or decreases

Answer. b

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