Arc Extension in Circuit Breakers - MCQs with answers

Arc Extension in Circuit Breakers - MCQs with answers

Q1. The heat produced at the contact point owing to flow of electric current is least affected by_____________________.

a. Temperature of the surrounding medium.
b. Contact resistance.
c. Magnitude of electric current flowing.
d. Duration of flow of current.

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Q2. Which of the following should have low value for the contacts and their material?

a. Thermal capacity.
b. Contact resistance.
c. Thermal conductivity.
d. None of above.

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Q3. In a circuit breaker, ionisation is facilitated by_________________.

a. Increase in field strength.
b. Increase in mean free length.
c. High temperature of the surrounding medium.
d. All of the above.

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Q4. In a circuit breaker the contact space is ionised by what?

a. Field emission from the contact surface.
b. Thermal emission from the contact surface.
c. Thermal ionisation of gas.
d. All of above.

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Q5. 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.

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Q6. 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.

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