Switchgear and Protection MCQ PDF Download

1. The frequency of carrier in the carrier current pilot scheme is in the range of

(a) 1 kHz to 10 kHz.
(b) 10 kHz to 25 kHz.
(c) 25 kHz to 50 kHz.
(d) 50 kHz to 500 kHz.

2. The frequency of carrier transmitted by microwave pilot is in the range of

(a) 1,000 kHz to 1,50G kHz
(b) 1000 kHz to 5,000 kHz
(c) 900 MHz to 6,000 MHz
(d) 10,000 MHz to 15,000 MHz

3. In carrier current protection the purpose of the wave-trap is for

(a) trapping power frequency waves.
(b) trapping high frequency waves entering into generators/ transformer unit.
(c) both (a) and (b).
(d) none of the above.

4. A line trap in carrier current relaying tuned to carrier frequency presents

(a) high impedance to carrier frequency but low impedance to power frequency.
(b) low impedance to both carrier and power frequency.
(c) high impedance to both carrier and power frequency.
(d) low impedance to carrier frequency but high impedance to power frequency.

5. A line trap in a long transmission line is used to

(a) improve the power factor.
(b) dampen the overvoltage oscillations.
(c) confine the carrier signals in the line.
(d) protect the line against direct lightning stroke.

6. Line trap and coupling capacitors are used for carrier current protection in which

(a) line trap has high impedance to 50 Hz signal but low impedance to carrier current signal whereas a coupling capacitor has low impedance to 50 Hz signal but high impedance to carrier signal.

(b) line trap has low impedance to 50 Hz signal but high impedance to carrier current signal, where as a coupling capacitor has high impedance to 50 Hz signal but low impedance to carrier signal.

(c) both the line trap and coupling capacitor have low impedance to 50 Hz signal but high impedance to carrier current signal.

(d) both the line trap and coupling capacitor have high impedance to 50 Hz signal but low impedance to carrier current signal.

7. In a 3-step distance protection, the reach of the three zones of the relay at the beginning of the first line typically extends into

(a) 100% of the first line, 50% of the second line and 20% of the third line.
(b) 80% of the first line, 50% of the second line and 20% of the third line.
(c) 80% of the first line, 50% of the second line and 10% of the third line.
(d) 50% of the first line, 50% of second line and 20% of the third line.

8. Distance protection scheme is preferred over graded time-lag over-current protection in HV and EHV lines because

(a) it is faster in operation.
(b) it is simple.
(c) it is cheaper in cost.
(d) all of the above.

9. Three step time-distance characteristic of distance relay can be had by

(a) changing taps on voltage transformer.
(b) separate measuring elements for zones 2 and 3.
(c) switching resistance in relay restraint circuit at pre-set time intervals by means of timer element.
(d) any of the above.

10. Lightning is a huge spark caused by electrical discharge taking place between

(a) clouds.
(b) within the same cloud.
(c) cloud and earth.
(d) any of the above.

11. Switching over-voltages are more hazardous than lightning surges in case of

(a) low voltage system.
(b) 33 kV system.
(c) EHV and UHV systems.
(d) all of these.

12. The overvoltage surges in power systems may be caused by

(a) lightning.
(b) resonance.
(c) switching.
(d) all of these.

13. Requirements of protection power station buildings against direct strokes are

(a) interception.
(b) conduction.
(c) dissipation.
(d) reflection and convection.
(e) (a), (b) and (c).

14. The protection against direct lightning strokes and high voltage steep waves is provided by

(a) ground wires.
(b) lightning arresters.
(c) lightning arresters and ground wires.
(d) earthing of neutral.

15. Which of the following factors should be considered in the design of a transmission line against lightning with ground wire?

(a) Mechanical strength of ground wire.
(b) Clearance between line conductor and ground wire.
(c) Clearance between line conductor and earth.
(d) All of the above.

16. For protection of rotating machines against lightning surges……….is used

(a) lightning arrester.
(b) capacitor.
(c) combination of lightning arrester and capacitor.
(d) lightning conductor and arrester.

17. Consider the following statements. To provide reliable protection for a distribution transformer against over-voltages using lightning arresters, it is essential that the

1. lead resistance is high.
2. distance between the transformer and the arrester is small. 3. transformer and the arrester have a common interconnecting ground.
3. spark-over voltage of the arrester is greater than the residual voltage.

Of these statements.
(a) 1, 3 and 4 are correct.
(b) 2 and 3 are correct.
(c) 2, 3 and 4 are correct.
(d) 1 and 4 are correct.

18. Impulse ratios of insulators and lightning arresters should be

(a) both low.
(b) high and low respectively.
(c) low and high respectively.
(d) both high.

19. Lighting arresters are used in power systems to protect electrical equipments against

(a) direct strokes of lightning.
(b) over-voltages due to indirect lightning stroke.
(c) power frequency over-voltages.
(d) over-currents due to lightning.

20. Which of the following is the protective device against lightning over-voltages?

(a) Rod gaps.
(b) Surge absorbers.
(c) Horn gaps.
(d) All of the above.