Switchgear and Protection - Electrical Engineering (MCQ) questions and answers

1)   What is the major cause of the failure of the circuit breaker?

a. Trip circuit open
b. Trip latch defective
c. Spring defective
d. All of these
Answer  Explanation 

ANSWER: All of these

Explanation:
No explanation is available for this question!


2)   For a high speed circuit breaker what will the total clearing time?

a. Few minutes.
b. Few seconds.
c. 1 to 2 cycles.
d. 5 to 20 cycles.
Answer  Explanation 

ANSWER: 1 to 2 cycles.

Explanation:
No explanation is available for this question!


3)   What is switchgear?

a. An apparatus used for switching, controlling and protecting the electrical circuits and equipments.
b. It detects the faults only.
c. It corrects the faults only.
d. All of the above.
Answer  Explanation 

ANSWER: All of the above.

Explanation:
No explanation is available for this question!


4)   Circuit breakers usually operate under

a. Steady short circuit current
b. Sub transient state of short circuit current
c. Transient state of short circuit current
d. None of these
Answer  Explanation 

ANSWER: Sub transient state of short circuit current

Explanation:
No explanation is available for this question!


5)   Refer to the following facts to answer the question

A 50 Hz, 11 kV, 3 phase alternator with earthed neutral having a reactance of 3 ohms per phase and is connected to a bus bar through a circuit breaker, if the distributed capacitance upto CB between the phase and neutral is 0.01 μ F.

What is the peak re striking voltage?


a. 18.36 kV
b. 17.96 kV
c. 15.96 kV
d. 12.65 kV
Answer  Explanation 

ANSWER: 17.96 kV

Explanation:
No explanation is available for this question!


6)   What should be the value of fusing factor?

a. Equal to zero
b. Equal to one
c. Less than one
d. More than one
Answer  Explanation 

ANSWER: Less than one

Explanation:
No explanation is available for this question!


7)   SF6 is which type of gas?

a. Electro positive
b. Electro negative
c. Both (a) and (b)
d. None of these
Answer  Explanation 

ANSWER: Both (a) and (b)

Explanation:
No explanation is available for this question!


8)   What is the purpose of back up protection?

a. To increase the speed
b. To increase the reach
c. To leave no blind spot
d. To guard against failure of primary
Answer  Explanation 

ANSWER: To guard against failure of primary

Explanation:
No explanation is available for this question!


9)   In a circuit breaker the contact space is ionised by what?

a. Field emission from the contact surface.
b. Thermal emission from the contact surface.
c. Thermal ionisation of gas.
d. All of above.
Answer  Explanation 

ANSWER: Thermal ionisation of gas.

Explanation:
No explanation is available for this question!


10)   Which of the following should have low value for the contacts and their material?

a. Thermal capacity.
b. Contact resistance.
c. Thermal conductivity.
d. None of above.
Answer  Explanation 

ANSWER: Contact resistance.

Explanation:
No explanation is available for this question!


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