# Arc Phenomenon in Circuit Breakers - MCQs with answers

## Arc Phenomenon in Circuit Breakers - MCQs with answers

Q1. When a fault occurs in a high voltage transmission line, what happens first?

a. Circuit breaker operates then the relay.
b. Relay operates and then the circuit breaker.
c. Relay operates, then successively the isolator and the circuit breaker.
d. Isolator operates, then successively the relay and the circuit breaker.

ANSWER: b. Relay operates and then the circuit breaker.

Q2. Which part of the circuit breaker is helpful in breaking the current?

a. Trip coil.
b. Contacts.
c. Medium
d. Handle.

Q3. Which type of tripping is generally preferred for the circuit breaker?

a. Manual
b. Automatically
c. Depending on the voltage level
d. None of the above

Q4. The arc resistance depends on which among the following factors?

a. Cross section of the arc.
b. Length of the arc.
c. Degree of ionisation
d. All of the above.

ANSWER: d. All of the above.

Q5. How is the initiation of electric arc at the instant of contact separation caused?

a. Thermionic emission of electrons.
b. Field emission of electrons.
c. Both (a) and (b)
d. None of these.

ANSWER: c. Both (a) and (b)

Q6. Arcing voltage will be the least in case of

a. Carbon
b. Copper
c. Silver
d. Tungsten

Q7. What is the arc voltage in a circuit breaker?

a. In phase with the arc current.
b. Lagging the arc current by 90°
c. Leading the arc current by 90°
d. Lagging the arcing current by 180°

ANSWER: a. In phase with the arc current.

Q8. What happens in the arc extinction using high resistance method?

a. Arc resistance is decreased with time.
b. Arc resistance is increased with time.
c. No change it remains same.
d. Arc resistance is kept zero.

ANSWER: b. Arc resistance is increased with time.

Q9. When using low resistance method for arc extension what is the value of arc resistance?

a. Arc resistance is zero.
b. Arc resistance is high
c. Arc resistance is low
d. Arc resistance is very high

ANSWER: c. Arc resistance is low

Q10. The resistance of an electric arc can be increased by

a. Increasing the concentration of ionised particles.
b. Reducing the arc length.
c. Splitting the arc.
d. Increasing the arc cross section.