Circuit Breakers MCQs

21. A 3 phase circuit is rated at 1200 A, 2000 MVA, 100 kV, 4sec. The rated symmetrical breaking current is

  1. 1.67 kA
  2. 20 kA
  3. 11.55 kA
  4. 300 kA

Answer
Answer. c

22. Bulk oil circuit breakers are suitable for:

  1. High voltage systems
  2. Low voltage systems
  3. Extra high voltage systems
  4. Medium voltage systems

Answer
Answer. a

23. In circuit breakers arcing is desirable:

  1. Only in oil circuit breaker before current zero
  2. After contact separation till current zero and also after current zero
  3. Only after contact separation till current zero
  4. Only in the post current zero period

Answer
Answer. c

24. Choose the correct statement about circuit breakers:

  1. The making capability of circuit breaker should be 2.55 times than breaking capability
  2. The making capability of circuit breaker should be equal to breaking capability
  3. The making capability of circuit breaker be $\sqrt{2}$ times than breaking capability
  4. The breaking capability of circuit should be 2.55 times than making capability

Answer
Answer. a

25. The resistance of are between the contacts of circuit breaker is increased by

  1. Increasing the cross-section area of the arc
  2. Splitting the arc in number of arcs in parallel
  3. Shortening the arc
  4. Splitting the arc in number of arcs in series

Answer
Answer. d

26. Which of the following circuit breakers has the highest dielectric strength?

  1. Bulk oil circuit breakers
  2. Air blast circuit breakers
  3. Minimum oil circuit breakers
  4. Vacuum circuit breakers

Answer
Answer. b

27. A 3-phase circuit breaker is rated at 1250 A, 2000 MVA, 33 kV. The making current will be

  1. 35 kA
  2. 49.44 kA
  3. 89 kA
  4. 69 kA

Answer
Answer. c

28. Why does minimum oil circuit breaker (CB) has less volume of oil?

  1. There is insulating between contacts
  2. The oil between the breaker contacts has greater strength
  3. Solid insulating material is provided
  4. None of these

Answer
Answer. a

29. The breaking current of a circuit breaker is

  1. Less than its making current
  2. More than its making current
  3. Equal to its making current
  4. None of the other options

Answer
Answer. a

30. The main purpose of using oil in the oil circuit breaker is to

  1. provide insulation between oil circuit breaker contacts
  2. provide cooling of contacts
  3. quenching arc
  4. none of these

Answer
Answer. c

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