MCQ on Switchgear and Protection

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

(a) 220 V
(b) 400 V
(c) 1000 V
(d) 10,000 V

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

(a) few minutes
(b) few seconds
(c) one second
(d) few cycles of supply voltage

3. When a HVAC circuit breaker is tested for endurance, it is tested for at least

(a) 1000 opening- closing operations
(b) 100 opening- closing operations
(c) 10 opening- closing operations
(d) 5 opening- closing operations

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

(a) 0.01 seconds
(b) 0.1 seconds
(c) 3 seconds
(d) 30 seconds

5. SF6 gas is

(a) yellow in color
(b) has pungent odor
(c) is highly toxic
(d) in non-inflammable

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

(a) 100 mm Hg
(b) 1 kg/cm²
(c) 3 to 5 kg/cm²
(d) 30 to 50 kg/cm²

7. SF6 gas

(a) is lighter than hydrogen
(b) is lighter than air
(c) has density 2 times as compared to that of air
(d) has density 5 times as compared to that of air

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

(a) 10 mm Hg
(b) 10^-2 mm Hg
(c) 10^-6 mm Hg
(d) 10^-9 mm Hg

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

(a) total operating time
(b) arcing time
(c) pre-arcing time
(d) any of the above.

10. Fusing factor of a HRC fuse is

(a) Minimum fusing current/Current rating
(b) Minimum fusing current/Minimum rupturing time
(c) Maximum fusing current/Minimum fusing current
(d) Minimum fusing current/Prospective current of a circuit

11. Under normal conditions, a circuit breaker should be inspected

(a) every day
(b) every week
(c) once in 6 months or 12 months
(d) once in 6 years to 7 years.

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

(a) 20 micro ohms ± 10
(b) 20 milli ohms ± 10
(c) 20 ohms ± 10
(d) 200 ohms ± 10

13. The insulation resistance of a high voltage circuit breaker is

(a) 1 kΩ
(b) 10 kΩ
(c) 20 Mega ohms
(d) 2000 Mega ohms

14. 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

(a) moisture
(b) dirty insulation surface
(c) carbon or copper particles sticking to the internal surface
(d) any of the above.

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

(a) recovery voltage
(b) restriking voltage
(c) supply voltage
(d) peak voltage.

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

(a) recovery voltage
(b) restriking voltage
(c) supply voltage
(d) peak voltage.

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

(a) power factor
(b) armature reaction
(c) circuit conditions
(d) all of the above.

18. A fuse wire posses

(a) inverse time characteristics
(b) direct time characteristics
(c) neither of the above.

19. Fuse protection is used for current ratings up to

(a) 10 A
(b) 20 A
(c) 50 A
(d) 100 A

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

(a) I α 1/D
(b) I α D
(c) I α D^3/2
(d) I α D²

21. A fuse wire should have

(a) low specific resistance and high melting point
(b) low specific resistance and low melting point
(c) high specific resistance and high melting point
(d) high specific resistance and low melting point

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

(a) 3 to 8
(b) 10 to 18
(c) 20 to 30
(d) 40 to 50

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

(a) Bulk oil circuit breaker
(b) Vacuum circuit breaker
(c) SF6 circuit breaker
(d) Minimum oil circuit breaker

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

(a) Aluminum
(b) Silver
(c) Lead
(d) Copper

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

(a) restriking current
(b) breaking current
(c) surge current
(d) recovery current

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

(a) Amperes
(b) Volts
(c) MW
(d) MWA

1. MCQ Questions on Electrical Cable
2. MCQ on Switchgear and Protection
3. Circuit Breaker MCQ Question Answer
4. Circuit Breaker Multiple Choice Questions

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