MCQ on Control and Protection

1. Relay contacts are normally made up of:

a) Silver contacts
b) Copper contacts
d) Lead contacts
c) Aluminum contacts

2.Sparking between the contacts can be reduced by inserting:

a) A capacitor in parallel with the contacts
b) A capacitor in series with the contacts
c) A resistor in the line
d) A reactor in the line

3.Arc chutes are used in:

a) Oil circuit breaker
b) Vacuum circuit breakers
c) SF6 circuit breakers
d) Air blast circuit breakers

4.A thermal protection switch is used to provide protection against:

a) Overload
b) Temperature
c) Short circuit
d) Over voltage

5. A circuit breaker is

(a) power factor correcting device
(b) a device to neutralize the effect of trans
(c) a waveform correcting device
(d) a current interrupting device

6.The medium employed for the extinction of arc in air circuit breaker is

(a) SF6
(b) Oil
(c) Air
(d) Water

7.The fault clearing time of a circuit breaker is usually

(a) few minutes
(b) few seconds
(c) one second
(d) few cycles of supply voltage

8. Low voltage circuit breakers have a rated voltage of less than

(a) 220 V
(b) 400V
(c) 1000 V
(d) 10,000 V

9. The contact resistance is least affected by:

a) Shape of the contact faces
b) Ambient temperature
c) Mechanical forces applied
d) Amount of surface commutation

10.The most efficient torque-producing actuating structure for induction-type relays is:

Shaded pole structure
b) Watt-hour meter structure
c) Induction cup structure
d) Single induction cup structure