# Power System Protection MCQ

Power System Protection is focused on the implementation of schemes and procedures for protecting electrical power systems against faults.

## The most dangerous fault

The most dangerous fault:

1. 3 phase fault
2. Line to line fault
3. Line to ground gault
4. Double line to ground fault

Correct answer: 1. 3 phase fault

## Heavy current fuses have wires that are in diameter than smaller ones

Heavy current fuses have wires that are _________ in diameter than smaller ones:

1. Larger
2. Smaller
3. Same
4. Any of above

## The pickup current of a relay having 125% current setting connected to 100/5 transformer is

The pickup current of a relay having 125% current setting connected to 100/5 transformer is:

1. 1 Amp
2. 5 Amp
3. 6.25 Amp
4. 10 Amp

## Which device signals the circuit breaker in case of fault

______________ signals circuit breaker in case of fault:

1. Fuse
2. Isolator
3. CT
4. Relay

## Buchholz relay is used for protection of

Buchholz relay is used for protection of:

1. Busbar
2. Transformer
3. Alternator
4. Motors

## While short-circuit test on circuit breaker a protection engineer obtained following readings on single frequency transient

While short-circuit test on circuit breaker a protection engineer obtained following readings on single frequency transient:

Time to reach the peak re-striking voltage = 50 µsec

Peak re-striking voltage = 150 kV

The average RRRV is:

1. 2.5 kV/µsec
2. 5 kV/µsec
3. 10 kV/µsec
4. 50 kV/µsec

Formula Hint: Average RRRV = Peak restriking voltage/Time to reach peak value

## What is the approximate value of the contact resistance of circuit breaker

What is approximate value of the contact resistance of circuit breaker:

1. 25 µΩ
2. 25 mΩ
3. 25 Ω
4. 250 Ω

Important Note: Contact resistance test of circuit breaker may not be the sole predictor of breaker thermal performance.

## Which of the following voltage surge is more harmful: 1/50 µs or 4/50 µs

Which of the following voltage surge is more harmful: 1/50 µs or 4/50 µs:

1. 1/50 µs is more harmful
2. 4/50 µs is more harmful
3. Both are equally armful
4. Insufficient data provided

Correct answer: 1. 1/50 µs is more harmful

Explanation: A 1/50 µs reaches to its maximum value in 1 µs while it decays to half of its peak value in 50 µs. While a 4/50 µs surge will reach to the maximum value in 4 µs while decays to half of its peak value in 50 µs.

## More MCQ Questions

More MCQ on Power System Protection: