Circuit Breakers Part 1 online MCQ

Circuit Breakers Part 1

Circuit Breakers Part one

Instructions: Click the answer button to see the correct answer.

1.A circuit breaker is

1. a device to neutralize the effect of transients
2. a waveform correcting device
3. power factor correcting device
4. a current interrupting device.

Answer: d

2. The function of protective relay in a circuit breaker is

1. to limit arcing current during the operation of circuit breaker
2. to close the contacts when the actuating quantity reaches a certain predetermined value
3. to provide additional safety in the operation of circuit breaker.
4. to each any stray voltages

Answer: b

3. Low voltage circuit breakers have rated voltage of less than

1. 10,000 V.
2. 1000 V
3. 400 V
4. 220 V

Answer: b

Circuit Breakers Part 1

4. The fault clearing time of a circuit breaker is usually

1. few cycles of supply voltage.
2. one second
3. few seconds
4. few minutes

Answer: a

5. The medium employed for extinction of arc in air circuit breaker is

1. Water.
2. Air
3. Oil
4. SF₆

Answer: b

6. Which of the following circuit breakers is preferred for EHT application

1. Bulk oil circuit breakers
2. Minimum oil circuit breakers
3. SF₆
4. Air blast circuit breakers

Answer: c

7. For high voltage, ac circuit breakers, the rated short circuit current is passed for

1. 30 seconds.
2. 0.1 sec
3. 3 seconds
4. 0.01 sec

Answer: c

8. Which of the following is not a type of the contractor for circuit breakers ?

1. Vacuum.
2. Electro-pneumatic
3. Pneumatic
4. Electro-magnetic

Answer: a

Circuit Breakers Part 1

9. Interrupting medium in a contractor may be

1. oil
2. air
3. SF₆
4. any of these

Answer: d

10 . In air blast circuit breakers, the pressure of air is of the order of

1. 200 to 300 kg/cm².
2. 1 kg/cm²
3. 20 to 30 kg/cm²
4. 100 mm Hg

Answer: c

11. SF₆ gas is

1. sulphur hexafluoride.
2. sulphur fluoride
3. sulphur hexafluorine
4. sulphur difluoride

Answer: a

Circuit Breakers Part 1

12. SF₆ gas

1. is yellow in color
2. has pungent odor
3. is non-inflammable.
4. is highly toxic

Answer: c

13. SF₆ gas

1. has density 5 limes as compared to that of air.
2. is lighter than air
3. has density 2-times as compared to that of air
4. is lighter than hydrogen

Answer: a

14. The pressure of SF₆ gas in circuit breakers is of the order of

1. 3 to 5 kg/cm²
2. 1 kg/cm²
3. 30 to 50 kg/cm²
4. 100 mm Hg

Answer: a

15. While selecting a gas for circuit breaker, the property of gas that should be considered is

1. non-toxicity
2. all of these
3. non-inflammability
4. high dielectric strength

Answer: b

Circuit Breakers Part 1

16. Out of the following circuit breakers, which one has the lowest voltage range

1. Air-blast circuit breaker
2. Tank type oil circuit breaker
3. Air-break circuit breaker
4. SF₆ circuit breaker.

Answer: c

17. Which of the following circuit breaker can be installed on 400 kV line

1. Vacuum circuit breaker
2. Tank type oil circuit breaker
3. Air blast circuit breaker.
4. Miniature circuit breaker

Answer: c

18. In a vacuum circuit breaker, the vacuum is of the order of

1. 10⁻⁶ mmHg
2. 10⁻⁹ mmHg
3. 10⁻² mmHg
4. 10 mmHg

Answer: b

Circuit Breakers Part 1

19. In modem EHV circuit breakers, the operating time between instant of receiving trip signal and final contact separation is, of the order of

1. 0.003 sec
2. 0.015 sec
3. 0.001 sec
4. 0.03 sec.

Answer: d

20. In a HRC fuse the time between cut-off and final current zero, is known as

1. pre-arcing time
2. arcing time
3. any of these
4. total operating time

Answer: b

21. Fusing factor for a HRC fuse is

1. Minimum fusing current / Prospective current of circuit.
2. Minimum fusing current / Minimum rupturing time
3. Maximum fusing current / Minimum fusing current
4. Minimum fusing current / Current rating

Answer: d

22. Which of the following circuit breakers does not use pneumatic operating mechanism

1. Air break circuit breaker
2. SF6 blast circuit breaker
3. Air blast circuit breaker
4. Bulk-oil circuit breaker.

Answer: d

Circuit Breakers Part 1

23. The contact resistance of a circuit breaker is. of the order of

1. 200 ohms ± 10.
2. 20milli ohms ± 10
3. 20 ohms ± 10
4. 20 micro ohms ± 10

Answer: d

24. The insulation resistance of high voltage circuit breaker is

1. 2000 Mega ohm.
2. 10 k Ohm
3. 20 Mega ohms
4. 1k Ohm

Answer: a

25. There is definite objection to use of which of the following medium for extinguishing the arc in case of a circuit breaker ?

1. Water.
2. SF6 gas
3. Air
4. Vacuum

Answer: a

26. In a circuit breaker if the insulation resistance between phase terminal and earthed frame is less than the specified limit, the probable cause could be

1. any of these
2. moisture
3. dirty insulation surface
4. carbon or copper particles sticking to the internal surface

Answer: a

27. If a circuit breaker does not operate on electrical compound, the probable reason could be

1. any of these
2. trip latch defective
3. spring defective
4. trip circuit open

Answer: a

Circuit Breakers Part 1

28. The normal frequency rms voltage that appears across the breaker poles after final arc extinction has occurred, is

1. re striking voltage
2. supply voltage
3. peak voltage.
4. recovery voltage

Answer: d

29. The transient voltage that appears across the contacts at the instant of arc extinction is called

1. recovery voltage
2. peak voltage.
3. re striking voltage
4. supply voltage

Answer: c

30. In a circuit breaker the active recovery voltage depends upon

1. circuit conditions
2. power factor
3. armature reaction
4. all of these

Answer: d

31. Best protection is provided by HRC fuses in case of

1. Short circuits
2. Overloads
3. Open circuits
4. None of these

Answer: a

Circuit Breakers Part 1

32. For motor circuit breakers, the time of closing the cycle is

1. 0.003 sec.
2. 0.01 sec
3. 0.10 sec
4. 0.001 sec

Answer: a

33. A relay used for protection of motors against overload is

1. Impedance relay
2. Buchholz’s relay.
3. Electromagnetic attraction type
4. Thermal relay

Answer: d

34. Fuse protection is used for current ratings up to

1. 20 A
2. 10 A
3. 50 A
4. 100 A.

Answer: d

35. The fuse current in amperes is related with fuse wire diameter D as

1. I ∞ D
2. I ∞ D²
3. I ∞ D³⁄²
4. I ∞ I/D

Answer: c

Circuit Breakers Part 1

36. The acting contacts for a circuit breakers are made of

1. Porcelain
2. Stainless steel
3. Hard pressed carbon
4. Copper tungsten alloy.

Answer: d

37. Ionization in a circuit breaker is not facilitated by

1. material of contacts
2. increase of field strength
3. high temperature of surrounding medium
4. increase of mean free path.

Answer: a

38. Which circuit breaker is generally used in railway traction ?

1. Vacuum circuit breaker
2. SF6 gas circuit breaker
3. Minimum oil circuit breaker.
4. Air break circuit breaker

Answer: d

39. A fuse wire should have

1. High specific resistance and low melting point.
2. High specific resistance and high melting point
3. Low specific resistance and low melting point
4. Low specific resistance and high melting point

Answer: a

Circuit Breakers Part 1

40. Fuse wire, protection, system is usually not used beyond

1. 10 A
2. 100A.
3. 50 A
4. 25 A

Answer: b

41. For extra high voltage lines which circuit breaker is preferred

1. SF6 gas circuit breaker
2. Vacuum circuit breaker
3. Minimum oil circuit breaker.
4. Bulk oil circuit breaker

Answer: a

42. The number of cycles in which a high speed circuit breaker can complete its operation is

1. 20 to 30
2. 40 to 50.
3. 3 to 8
4. 10 to 18

Answer: c

43. A material best suited for manufacturing of fuse wire is

1. Silver
2. Aluminium
3. Copper.
4. Lead

Answer: a

44. In a circuit breaker the current which exists at the instant of contact separation is known as

1. recovery current.
2. re striking current
3. surge current
4. breaking current

Answer: d

Circuit Breakers Part 1

45. A Merz-price protection is suitable for

1. feeders
2. transformers
3. transmission lines.
4. alternators

Answer: d

46. ‘Kick fuse’ has

1. all of these
2. inverse characteristics.
3. square law characteristics
4. linear characteristics

Answer: b

47. Air blast circuit breakers for 400 kV. Power system are designed to operate in

1. 50 seconds.
2. 50 milli seconds
3. 500 milli seconds
4. 50 micro seconds

Answer: b

48. Breaking capacity of a circuit breaker is usually expressed in terms of

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

Answer: d

Circuit Breakers Part 1

49. Sulphur hexafluoride is a

1. Inactive gas
2. Conductor of electricity
3. Dielectric.
4. Semi-conductor

Answer: c

50. The contact resistance is least affected by

1. the ambient temperature.
2. the amount of surface contamination
3. the shape of the contact faces
4. the mechanical force applied

Answer: a