# Switch Gear and Protection 4

Electrical Engineering MCQ Question Papers: Campus Placement

Subject: Switch Gear and Protection 4

Part 4: List for questions and answers of Switch Gear and Protection

Q1. 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

Q2. 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

Q3. What is restricting 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

Q4. 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

Q5. On what factor does the rate of rise of restricting voltage (RRRV) depend?

a) System voltage

b) Circuit power factor only

c) Switching conditions

d) Both (b) and (c)

Q6. Rate of rise of restriping voltage depend on_____________?

a) Type of circuit breaker

b) Capacitance of the system

c) Inductance of the system

d) Both (b) and (c)

Q7. 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)

Q8. 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

Q9. 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

Q10. What is the interrupting medium in the contactor?

a) Air at atmospheric pressure

b) SF6 gas

c) Oil

d) All of the above

Q11. How is the restriking voltage measured?

a) RMS value

b) Peak value

c) Instantaneous value

d) Average value

Q12. 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

Q13. 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 – 50 u sec

B. The peak re striking voltage, 100 kV

frequency of oscillations is ?

a) 100 Hz

b) 1,000 Hz

c) 10,000 Hz

d) 10 Hz

Q14. 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

Q15. A 50 Hz 3 phase synchronous generator has inductance per phase of 15mH. The

capacitance of generator and the circuit breaker is 0.002? F. What is the natural frequency

of oscillation?

a) 29 kHz

b) 2.9 kHz

c) 290 kHz

d) 29 MHz

Q16. 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

Q17. 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

Q18. 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

Q19. 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

Q20. The air blast circuit breakers for 400 kV systems are designed to operate in how much

time?

a) 1.0 s

b) 0.5 s

c) 50 ms

d) 100 us

Part 4: List for questions and answers of Switch Gear and Protection