# Switchgear and Protection Test Question - 2

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  Explanation  Related Ques ANSWER: Energizing the trip circuit and the arc extension on an opening operation. 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  Related Ques ANSWER: 1 to 2 cycles. Explanation: No explanation is available for this question!

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  Explanation  Related Ques ANSWER: The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction. Explanation: No explanation is available for this question!

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
 Answer  Explanation  Related Ques ANSWER: Both (a) and (b) Explanation: No explanation is available for this question!

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).
 Answer  Explanation  Related Ques ANSWER: Both (b) and (c). Explanation: No explanation is available for this question!

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
 Answer  Explanation  Related Ques ANSWER: Both (b) and (c) Explanation: No explanation is available for this question!

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
 Answer  Explanation  Related Ques ANSWER: Both (b) and (c) Explanation: No explanation is available for this question!

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  Explanation  Related Ques ANSWER: The restriking voltage can be high. Explanation: No explanation is available for this question!

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
 Answer  Explanation  Related Ques ANSWER: Final arc extinction Explanation: No explanation is available for this question!

10)   What is the interrupting medium in the contactor?

a. Air at atmospheric pressure.
b. SF6 gas
c. Oil
d. All of the above.
 Answer  Explanation  Related Ques ANSWER: All of the above. Explanation: No explanation is available for this question!

11)   How is the restriking voltage measured?

a. RMS value
b. Peak value
c. Instantaneous value
d. Average value
 Answer  Explanation  Related Ques ANSWER: Peak value Explanation: No explanation is available for this question!

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. instantaneous value, rms value
c. rms value, instantaneous value
d. instantaneous value, instantaneous value
 Answer  Explanation  Related Ques ANSWER: instantaneous value, instantaneous value Explanation: No explanation is available for this question!

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
 Answer  Explanation  Related Ques ANSWER: 2*106kV/sec Explanation: No explanation is available for this question!

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
 Answer  Explanation  Related Ques ANSWER: 10,000 Hz Explanation: No explanation is available for this question!

15)   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  Related Ques ANSWER: 17.96 kV Explanation: No explanation is available for this question!

16)   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 frequency of oscillations?

a. 10000 Hz
b. 12500 Hz
c. 12628 Hz
d. 13265 Hz
 Answer  Explanation  Related Ques ANSWER: 12628 Hz Explanation: No explanation is available for this question!

17)   What is the average rate of rise of restriking voltage upto the first peak?

a. 525 * 103kV / sec
b. 453 * 103kV / sec
c. 582 * 103 kV / sec
d. 467 * 103 kV / sec
 Answer  Explanation  Related Ques ANSWER: 453 * 103kV / sec Explanation: No explanation is available for this question!

18)   A 50 Hz 3 phase synchronous generator has inductance per phase of 15mH. The capacitance of generator and the circuit breaker is 0.002μ F. What is the natural frequency of oscillation?

a. 29 kHz
b. 2.9 kHz
c. 290 kHz
d. 29 MHz
 Answer  Explanation  Related Ques ANSWER: 29 kHz Explanation: No explanation is available for this question!

19)   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)
 Answer  Explanation  Related Ques ANSWER: 0.5*√(L/C) Explanation: No explanation is available for this question!

20)   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.
 Answer  Explanation  Related Ques ANSWER: Air free from moisture Explanation: No explanation is available for this question!

21)   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.
 Answer  Explanation  Related Ques ANSWER: A transformer on no load is switched off. Explanation: No explanation is available for this question!

22)   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  Explanation  Related Ques ANSWER: Damp out the fast transient. Explanation: No explanation is available for this question!

23)   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  Explanation  Related Ques ANSWER: The blast of air cuts across the arc. Explanation: No explanation is available for this question!

24)   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
 Answer  Explanation  Related Ques ANSWER: 50 ms Explanation: No explanation is available for this question!

25)   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  Explanation  Related Ques ANSWER: High pressure to low pressure. Explanation: No explanation is available for this question!

26)   What is the breaking capacity of the air blast circuit breaker?

a. 5000 MVA
b. 6000 MVA
c. 7000 MVA
d. 10000 MVA
 Answer  Explanation  Related Ques ANSWER: 7000 MVA Explanation: No explanation is available for this question!

27)   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
 Answer  Explanation  Related Ques ANSWER: Both (a) and (c) Explanation: No explanation is available for this question!

28)   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
 Answer  Explanation  Related Ques ANSWER: Both (a) and (b) Explanation: No explanation is available for this question!

29)   SF6 is which type of gas?

a. Electro positive
b. Electro negative
c. Both (a) and (b)
d. None of these
 Answer  Explanation  Related Ques ANSWER: Both (a) and (b) Explanation: No explanation is available for this question!

30)   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
 Answer  Explanation  Related Ques ANSWER: 2.8 kg / cm2 Explanation: No explanation is available for this question!

31)   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
 Answer  Explanation  Related Ques ANSWER: Is highly electronegative gas Explanation: No explanation is available for this question!

32)   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  Explanation  Related Ques ANSWER: Gets decomposed to SF4 and SF2 Explanation: No explanation is available for this question!

33)   SF6 gas is imported in _____________.

a. Air cylinders
b. Gas cylinders
c. Liquid form in cylinders
d. Solid form.
 Answer  Explanation  Related Ques ANSWER: Liquid form in cylinders Explanation: No explanation is available for this question!

34)   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  Explanation  Related Ques ANSWER: Low conductivity and high vapour pressure. Explanation: No explanation is available for this question!

35)   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
 Answer  Explanation  Related Ques ANSWER: Vacuum circuit breaker Explanation: No explanation is available for this question!

36)   For rural electrification in India, which circuit breaker is generally used?

a. Oil
b. SF6
c. Vacuum
d. Air blast
 Answer  Explanation  Related Ques ANSWER: Vacuum Explanation: No explanation is available for this question!

37)   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
 Answer  Explanation  Related Ques ANSWER: Current goes through zero Explanation: No explanation is available for this question!

38)   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.
 Answer  Explanation  Related Ques ANSWER: All of these. Explanation: No explanation is available for this question!

39)   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
 Answer  Explanation  Related Ques ANSWER: Quenching arc. Explanation: No explanation is available for this question!

40)   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  Explanation  Related Ques ANSWER: Close the contacts when the actuating quantity attains a certain predetermined value. Explanation: No explanation is available for this question!