Protection and Switchgear Quiz 2

What is the major cause of the failure of the circuit breaker?

• Trip circuit open

• Trip latch defective

• Spring defective

• All of these

For a high speed circuit breaker what will the total clearing time?

• Few minutes

• Few seconds

• 1 to 2 cycles

• 5 to 20 cycles

Circuit breakers usually operate under

• Steady short circuit current

• Sub transient state of short circuit current

• Transient state of short circuit current

• None of these

SF6 is which type of gas?

• Electro positive

• Electro negative

• Both (a) and (b)

• None of these

What is the purpose of back up protection?

• To increase the speed

• To increase the reach

• To leave no blind spot

• To guard against failure of primary

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

• Thermal ionisation of metal

• Thermal emission from the contact surface

• Thermal ionisation of gas

• All of above

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

• Thermal capacity

• Contact resistance

• Thermal conductivity

• None of above

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

• Field emission of electrons

• Thermionic emission of electrons

• Both (a) and (b)

• None of these

The arc resistance depends on which among the following factors?

• Cross section of the arc

• Length of the arc

• Degree of ionization

• All of the above

Which of the following circuit breakers is used for the railway electrification?

• Air blast circuit breaker

• SF6 circuit breaker

• Bulk oil circuit breaker

• Minimum oil circuit breaker