# Power Systems Switchgear Expected MCQ PDF 2 For Coal India Limited (CIL) MT Exam 2017

## Power Systems Switchgear Expected MCQ PDF 2

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Attempt Free Power Systems Switchgear Expected MCQ PDF 2 Here. Read The Important Electrical MCQ From Below.

1)   The interrupting time of a circuit breaker is the period between the instant of _________.
a. Initiation of short circuit and the arc extinction on an opening operation.
b. Energizing the trip circuit and the arc extension on an opening operation.
c. Initiation of short circuit and the parting of primary arc contacts.
d. Energizing of the trip circuit and the parting of primary arc contacts.

ANSWER: Energizing the trip circuit and the arc extension on an opening operation.

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.

3)   What is restriking voltage?
a. The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction.
b. The transient voltage that appears across the circuit breaker contacts at the end of arc extinction.
c. Both (a) and (b)
d. None of the above

ANSWER: The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction.

Power Systems Switchgear Expected MCQ PDF 2

4)   In a circuit breaker, the active recovery voltage depends upon which among these?
a. Circuit conditions.
b. Power factor.
c. Both (a) and (b)
d. None of the above

5)   On what factor does the rate of rise of restriking voltage (RRRV) depend?
a. System voltage.
b. Circuit power factor only
c. Switching conditions
d. Both (b) and (c).

6)   Rate of rise of restriking voltage depend on_____________?
a. Type of circuit breaker.
b. Capacitance of the system.
c. Inductance of the system.
d. Both (b) and (c)
e. None of these

Power Systems Switchgear Expected MCQ PDF 2

7)   The stability of arc in vacuum depends on _________.
a. The contact material only.
b. The circuit parameters only.
c. The contact materials and its vapour pressure.
d. Both (b) and (c)
e. None of these

8)   Why is it difficult to interrupt a capacitive circuit?
a. The current has a leading power factor.
b. The restriking voltage can be high.
c. Current magnitude is very small.
d. Stored energy in the capacitor is very high.

ANSWER: The restriking voltage can be high.

9)   Recovery voltage is the value of rms voltage that reappears across the poles of a circuit breaker before_______________
a. Restriking voltage
b. Final arc extinction
c. Rise of voltage
d. All of the above

Power Systems Switchgear Expected MCQ PDF 2

10)   What is the interrupting medium in the contactor?
a. Air at atmospheric pressure.
b. SF6 gas
c. Oil
d. All of the above.

11)   How is the restriking voltage measured?
a. RMS value
b. Peak value
c. Instantaneous value
d. Average value

12)   The making and breaking currents of a 3 phase ac circuit breakers in power systems are respectively in ________form.
a. rms value, rms value
b. Peak Value, rms value
c. rms value, instantaneous value
d. instantaneous value, instantaneous value

Power Systems Switchgear Expected MCQ PDF 2

13)   In a short circuit test on a circuit breaker, the following readings were obtained on single frequency transients
a. Time to reach the peak re striking voltage – 50μ sec
b. The peak re striking voltage, 100 kV
What is its average RRRV?
a. 2*106kV/sec
b. 3*105kV/sec
c. 2*105kV/sec
d. 3*106kV/sec

14)   In a short circuit test on a circuit breaker, the following readings were obtained on single frequency transients
a. Time to reach the peak re striking voltage – 50μ sec
b. The peak re striking voltage, 100 kV what will be the frequency of oscillations?
a. 100 Hz
b. 1,000 Hz
c. 10,000 Hz
d. 10 Hz

Power Systems Switchgear Expected MCQ PDF 2

15)   For the following figure shows a CB circuit with L – C introducing a damping circuit. For the critical damping what is the value of r?

a. √(LC)
b. 0.5*√(C/L)
c. 0.5*√(L/C)
d. 2π*√(L/C)

16)   Which type of air is used in air blast circuit breaker?
a. Ionised air
b. Air free from moisture
c. Air should have least CO2
d. Air must have oil mist.

17)   When using air blast circuit breaker, current chopping is a phenomenon observed when
a. A long overhead line is switched off.
b. A bank of capacitors is switched off.
c. A transformer on no load is switched off.
d. A heavy load is switched off.

18)   Why is the resistance switching used in a air blast circuit breaker?
a. Reduce the magnitude of fault current.
b. Control the CB operating time.
c. Damp out the fast transient.
d. Change the fault current power factor.

ANSWER: Damp out the fast transient.

Power Systems Switchgear Expected MCQ PDF 2

19)   What is the type of air blast in cross blast type CB?
a. The blast of air is along the arc.
b. The blast of air cuts across the arc.
c. Both (a) and (b)
d. None of the above.

ANSWER: The blast of air cuts across the arc.

20)   The air blast circuit breakers for 400 kV systems are designed to operate in how much time?
a. 0.1 s
b. 0.5 s
c. 50 ms
d. 100µs

21)   In axial blast type of CB, expansion of air takes place from ______________.
a. High pressure to low pressure.
b. Low pressure to high pressure.
c. Always in high pressure.
d. Always in low pressure.

ANSWER: High pressure to low pressure.

Power Systems Switchgear Expected MCQ PDF 2

22)   What is the breaking capacity of the air blast circuit breaker?
a. 5000 MVA
b. 6000 MVA
c. 7000 MVA
d. 10000 MVA

23)   Why do the SF6 gases have an excellent heat transfer property?
a. Low gaseous viscosity.
b. High dielectric strength.
c. Higher molecular weight.
d. Both (a) and (c)
e. None of these

24)   What is the major drawback of using SF6 circuit breakers?
a. Sealing problems of the gas.
b. Ingress of moisture in the gas system – dangerous.
c. Deterioration of SF6 gas with time.
d. Both (a) and (b)
e. None of these

25)   SF6 is which type of gas?
a. Electro positive
b. Electro negative
c. Both (a) and (b)
d. None of these

Power Systems Switchgear Expected MCQ PDF 2

26)   What is the normal pressure at which the SF6 gas is maintained in the closed position of the breaker?
a. 2 kg / cm2
b. 2.5 kg /cm2
c. 2.8 kg / cm2
d. 3 kg / cm2

27)   What is the most important property which makes the SF6 very efficient medium for circuit breaking?
a. Is non toxic and non inflammable.
b. Has a high dielectric constant.
c. Has a high breakdown strength
d. Is highly electronegative gas

28)   During arc extinction SF6 gas gets converted to which among these?
a. Gets decomposed to SF4 and SF2
b. Gets decomposed to S and F
c. Gets reduced to SF6
d. Gets oxidized

ANSWER: Gets decomposed to SF4 and SF2

29)   SF6 gas is imported in _____________.
a. Air cylinders
b. Gas cylinders
c. Liquid form in cylinders
d. Solid form.

Power Systems Switchgear Expected MCQ PDF 2

30)   To limit current chopping in vacuum circuit breakers, the contact material employed should have the properties of
a. Low conductivity and high vapour pressure.
b. Low conductivity and low vapour pressure.
c. High conductivity and high vapour pressure.
d. High conductivity and low vapour pressure.

ANSWER: Low conductivity and high vapour pressure.

31)   Keeping in view the cost and the overall effectiveness, which of the following circuit breaker is best suited for capacitor bank switching?
a. Vacuum circuit breaker
b. Air blast CB
c. SF6
d. Oil CB

32)   For rural electrification in India, which circuit breaker is generally used?
a. Oil
b. SF6
c. Vacuum
d. Air blast

Power Systems Switchgear Expected MCQ PDF 2

33)   When does the arc interruption in oil circuit breaker take place?
a. Contacts apart.
b. Voltages becomes zero
c. Current goes through zero
d. All of the above

34)   What is the advantage of using oil as the arc quenching medium?
a. Good cooling properties.
b. High dielectric strength.
c. Acts as an insulator.
d. All of these.

35)   What is the main purpose of oil in oil circuit breakers?
a. Provide insulation
b. Quenching arc.
c. Provide cooling of contacts.
d. None of the above

36)   What does protective relay provide?
a. Provide additional safety to the circuit breaker in its operation.
b. Close the contacts when the actuating quantity attains a certain predetermined value.
c. Limit the arcing current during the circuit breaker operation.
d. Earth or ground any stray voltage.

ANSWER: Close the contacts when the actuating quantity attains a certain predetermined value.

Power Systems Switchgear Expected MCQ PDF 2