MCQ on Protection and switch gear

A three phase transformer having a line voltage ratio of 400/33000 V is connected in the star-delta. The CTs on the 400V side have a CT ratio of 1000/5. What must be the ratio of CTs on the 33000 side?

• a) 7/5

• b) 5/7

• c) 3/5

• d) 5/2

What is switchgear?

• a. An apparatus used for switching, controlling and protecting the electrical circuits and equipments.

• b. It detects the faults only.

• c. It corrects the faults only.

• d. All of the above.

SF6 is which type of gas?

• a. Electro positive

• b. Electro negative

• c. Both (a) and (b)

• d. None of these

The arc resistance depends on which among the following factors?

• a. Cross section of the arc.

• b. Length of the arc.

• c. Degree of ionization

• d. All of the above.

What is the average rate of rise of restriking voltage upto the first peak?

• a. 525 * 103kV / sec

• b. 453 * 103kV / sec

• c. 582 * 103 kV / sec

• d. 467 * 103 kV / sec

What is the making capacity of the circuit breaker?

• a. Less than the asymmetrical breaking capacity of the breaker

• b. Greater than the asymmetrical breaking capacity of the breaker

• c. Equal to the asymmetrical breaking capacity of the breaker

• d. Equal to the symmetrical breaking capacity of the breaker

What is the cut off current in the fuse?

• a. Maximum value actually reached.

• b. Rms value actually reached.

• c. Average value actually reached.

• d. None of the above

Why are the isolators used?

• a. Break abnormal current

• b. Making under fault conditions

• c. Breaking the circuit under no load condition

• d. None of the above

Which of the following circuit breaker is highly reliable and has a least maintenance?

• a. Oil circuit breakers

• b. Air blast

• c. Vacuum circuit breakers

• d. SF6 circuit breakers

What is the cuWhat is the cut off current in the fuse?

t off current in the fuse?

• Maximum value actually reached.

• . Rms value actually reached

• Average value actually reached

•     None of the above