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MCQs 1: What is the breaking capacity of the air blast circuit breaker?

5000 MVA 6000 MVA 7000 MVA 10000 MVA
Answer Explanation

MCQs 2: To limit current chopping in vacuum circuit breakers, the contact material employed should have the properties of

Low conductivity and high vapour pressure. Low conductivity and low vapour pressure. High conductivity and high vapour pressure. High conductivity and low vapour pressure.
Answer Explanation

MCQs 3: When does the arc interruption in oil circuit breaker take place?

Contacts apart. Voltages becomes zero Current goes through zero All of the above
Answer Explanation

MCQs 4: What is the advantage of using oil as the arc quenching medium?

Good cooling properties. High dielectric strength. Acts as an insulator. All of these.
Answer Explanation

MCQs 5: What is the main purpose of oil in oil circuit breakers?

Provide insulation Quenching arc. Provide cooling of contacts. None of the above
Answer Explanation

MCQs 6: What does protective relay provide?

Provide additional safety to the circuit breaker in its operation. Close the contacts when the actuating quantity attains a certain predetermined value. Limit the arcing current during the circuit breaker operation. Earth or ground any stray voltage.
Answer Explanation

MCQs 7: What is / are the main disadvantage / s of using oil as the quenching medium in the circuit breakers?

Need periodical replacement. Risk of formation of explosive mixture with air. Possibility of causing fire hazards. All of the above.
Answer Explanation

MCQs 8: A three phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3s. What is its symmetrical breaking current?

1200 A 3600 A 35 kA 104.8 kA
Answer Explanation

MCQs 9: A thermal protection switch provides protection against what?

Overload Temperature Short circuit Over voltage
Answer Explanation

MCQs 10: 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
Answer Explanation

MCQs 11: Which among these circuit breakers produce the least arc energy?

Plain oil Minimum oil Air blast Air break
Answer Explanation

MCQs 12: The rating of the circuit breaker is usually determined on the basis of ____________ fault.

Symmetrical Line to line Single line to ground Double line to ground
Answer Explanation

MCQs 13: 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
Answer Explanation

MCQs 14: What is the making capacity of the circuit breaker?

Less than the asymmetrical breaking capacity of the breaker Greater than the asymmetrical breaking capacity of the breaker Equal to the asymmetrical breaking capacity of the breaker Equal to the symmetrical breaking capacity of the breaker
Answer Explanation

MCQs 15: A three phase circuit breaker is rated 2000 MVA, 33 kV. What will be its making current?

35 kA 49 kA 70 kA 89 kA
Answer Explanation

MCQs 16: What is the making to breaking current ratio for an extra high voltage circuit breaker?

More than 1 Equal to 1 Less than 1 A negative value
Answer Explanation

MCQs 17: Why is an isolator installed?

To isolate one portion of the circuit from another As an substitute for the circuit breaker It used on either sides of the circuit breaker Both (a) and (c) None of these
Answer Explanation

MCQs 18: For which among the following the current ratings are not required?

Circuit breakers Relays Isolators Load break switch
Answer Explanation

MCQs 19: The isolators used in the transmission lines are capable of breaking

Fault current No current Charging current Load current
Answer Explanation

MCQs 20: Why are the isolators used?

Break abnormal current Making under fault conditions Breaking the circuit under no load condition None of the above
Answer Explanation

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