1) What is / are the main disadvantage of using oil as the quenching medium in the circuit breakers?a. Need periodical replacement.b. Risk of formation of explosive mixture with air.c. Possibility of causing fire hazards.d. All of the above.

ANSWER: All of the above.

2) A three phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3s. What is its symmetrical breakingcurrent?a. 1200 Ab. 3600 Ac. 35 kAd. 104.8 kA

ANSWER: 35 kA

3) A thermal protection switch provides protection against what?a. Overloadb. Temperaturec. Short circuitd. Over voltage

ANSWER: Overload

4) Which of the following circuit breakers is used for the railway electrification?a. Air blast circuit breakerb. SF6 circuit breakerc. Bulk oil circuit breakerd. Minimum oil circuit breaker

ANSWER: Air blast circuit breaker

1/9

5) Which circuit breaker is preferred to be installed in extra high voltage AC system?a. Bulk oil type circuit breakerb. Air blast circuit breakerc. SF6 circuit breakerd. Vacuum circuit breaker

ANSWER: SF6 circuit breaker

6) Which among these circuit breakers produce the least arc energy?a. Plain oilb. Minimum oilc. Air blastd. Air break

ANSWER: Air blast

7) The rating of the circuit breaker is usually determined on the basis of ____________ fault.a. Symmetricalb. Line to linec. Single line to groundd. Double line to ground

ANSWER: Symmetrical

8) Which of the following circuit breaker is highly reliable and has a least maintenance?a. Oil circuit breakersb. Air blastc. Vacuum circuit breakersd. SF6 circuit breakers

ANSWER: SF6 circuit breakers

2/9

9) Circuit breakers usually operate undera. Steady short circuit currentb. Sub transient state of short circuit currentc. Transient state of short circuit currentd. None of these

ANSWER: Sub transient state of short circuit current

10) What is the making capacity of the circuit breaker?a. Less than the asymmetrical breaking capacity of the breakerb. Greater than the asymmetrical breaking capacity of the breakerc. Equal to the asymmetrical breaking capacity of the breakerd. Equal to the symmetrical breaking capacity of the breaker

ANSWER: Greater than the asymmetrical breaking capacity of the breaker

11) A three phase circuit breaker is rated 2000 MVA, 33 kV. What will be its making current?a. 35 kAb. 49 kAc. 70 kAd. 89 kA

ANSWER: 89 kA

12) The breaking capacity of a three phase circuit breaker is given bya. Service line voltage * rated symmetrical current in amperes * 10 -6 MVAb. √3 * Service line voltage * rated symmetrical current in amperes * 10 -6 MVAc. 1.1* Service line voltage * rated symmetrical current in amperes * 10 -6 MVAd. √2 * Service line voltage * rated symmetrical current in amperes * 10 -6 MVA

ANSWER: √3 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA

3/9

13) Assertion (A): In comparison to making capacity of a circuit breaker its breaking capacity is normallyhigher.Reason (R): The breaking capacity of a CB is expressed as √3 * VI * 10 -6 MVAa. Both A and R are true and R is the correct explanation of Ab. Both A and R are true and R is not the explanation of Ac. A is true but R is falsed. A is false but R is true.

ANSWER: A is false but R is true.

14) What is the making to breaking current ratio for an extra high voltage circuit breaker?a. More than 1b. Equal to 1c. Less than 1d. A negative value

ANSWER: More than 1

15) Why is an isolator installed?a. To isolate one portion of the circuit from anotherb. As an substitute for the circuit breakerc. It used on either sides of the circuit breakerd. Both (a) and (c)e. None of these

ANSWER: To isolate one portion of the circuit from another

16) For which among the following the current ratings are not required?a. Circuit breakersb. Relaysc. Isolatorsd. Load break switch

ANSWER: Isolators

4/9

17) The isolators used in the transmission lines are capable of breakinga. Fault currentb. No currentc. Charging currentd. Load current

ANSWER: Charging current

18) Why are the isolators used?a. Break abnormal currentb. Making under fault conditionsc. Breaking the circuit under no load conditiond. None of the above

ANSWER: Breaking the circuit under no load condition

19) What is the major cause of the failure of the circuit breaker?a. Trip circuit openb. Trip latch defectivec. Spring defectived. All of these

ANSWER: All of these

20) What is the purpose of back up protection?a. To increase the speedb. To increase the reachc. To leave no blind spotd. To guard against failure of primary

ANSWER: To guard against failure of primary

5/9

21) What is the actuating quantity for the relays?a. Magnitudeb. Frequencyc. Phase angled. All of these

ANSWER: All of these

22) Protective relays can be designed to respond to ___________.a. Light intensity, impedanceb. Temperature, resistance, reactancec. Voltage and currentd. All of these

ANSWER: All of these

23) On what factor does the operating speed of the relay depend?a. Rate of flux built upb. Armature core air gapc. Spring tensiond. All of these

ANSWER: All of these

24) In the following figure, the relay circuit is divided into three parts. What does the first part consist of?

a. Primary winding of a current CT which is connected inseries with the line to be protected.b. Secondary of the CT and the operating coil.c. Tripping circuit.d. None of these

ANSWER: Primary winding of a current CT which isconnected in series with the line to be protected.

6/9

25) In the following figure, the relay circuit is divided into three parts. What does the third part consistof?a. Primary winding of a current CT which is connected inseries with the line to be protected.b. Secondary of the CT and the operating coil.c. Tripping circuit.d. None of these

ANSWER: Tripping circuit.

26) In the following figure, which component ensures the safety of the line from damage?a. Relayb. Circuit breakerc. Bus bard. Current transformer

ANSWER: Relay

27) In the following figure, the tripping circuit is__________.a. ACb. DCc. Either AC or DCd. None of these

ANSWER: Either AC or DC

28) Plug setting of a electromagnetic relay can be altered by varyinga. Number of ampere turnsb. Air gap of magnetic pathc. Adjustable back stopd. None of these

ANSWER: Number of ampere turns

7/9

29) The most efficient torque producing actuating structure for the induction type relays isa. Shaded pole structureb. Watt hour meter structurec. Induction cup structured. Single induction loop structure

ANSWER: Induction cup structure

30) Which of the following circuit breakers has the lowest operating voltage?a. SF6 circuit breakerb. Air breakc. Air blastd. Minimum oil circuit breaker

ANSWER: Air break

8/9

9/9

1) 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.

ANSWER: Energizing the trip circuit and the arc extension on an opening operation.

2) 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.

ANSWER: 1 to 2 cycles.

3) What is restriking voltage?

a. The transient voltage that appears across the circuit breaker contacts at the instant of arc

extinction.

b. The transient voltage that appears across the circuit breaker contacts at the end of arc

extinction.

c. Both (a) and (b)

d. None of the above

ANSWER: The transient voltage that appears across the circuit breaker contacts at the

instant of arc extinction.

4) In a circuit breaker, the active recovery voltage depends upon which among these?

a. Circuit conditions.

b. Power factor.

c. Both (a) and (b)

d. None of the above

ANSWER: Both (a) and (b)

5) On what factor does the rate of rise of restriking voltage (RRRV) depend?

a. System voltage.

b. Circuit power factor only

c. Switching conditions

d. Both (b) and (c).

ANSWER: Both (b) and (c).

6) Rate of rise of restriking voltage depend on_____________?

a. Type of circuit breaker.

b. Capacitance of the system.

c. Inductance of the system.

d. Both (b) and (c)

e. None of these

ANSWER: Both (b) and (c)

7) The stability of arc in vacuum depends on _________.

a. The contact material only.

b. The circuit parameters only.

c. The contact materials and its vapour pressure.

d. Both (b) and (c)

e. None of these

ANSWER: Both (b) and (c)

8) Why is it difficult to interrupt a capacitive circuit?

a. The current has a leading power factor.

b. The restriking voltage can be high.

c. Current magnitude is very small.

d. Stored energy in the capacitor is very high.

ANSWER: The restriking voltage can be high.

9) Recovery voltage is the value of rms voltage that reappears across the poles of a circuit

breaker before_______________

a. Restriking voltage

b. Final arc extinction

c. Rise of voltage

d. All of the above

ANSWER: Final arc extinction

10) What is the interrupting medium in the contactor?

a. Air at atmospheric pressure.

b. SF6 gas

c. Oil

d. All of the above.

ANSWER: All of the above.

11) How is the restriking voltage measured?

a. RMS value

b. Peak value

c. Instantaneous value

d. Average value

ANSWER: Peak value

12) The making and breaking currents of a 3 phase ac circuit breakers in power systems

are respectively in ________form.

a. rms value, rms value

b. instantaneous value, rms value

c. rms value, instantaneous value

d. instantaneous value, instantaneous value

ANSWER: instantaneous value, instantaneous value

13) In a short circuit test on a circuit breaker, the following readings were obtained on

single frequency transients

a. Time to reach the peak re striking voltage - 50µ sec

b. The peak re striking voltage, 100 kV

What is its average RRRV?

a. 2*106kV/sec

b. 3*105kV/sec

c. 2*105kV/sec

d. 3*106kV/sec

ANSWER: 2*106kV/sec

14) In a short circuit test on a circuit breaker, the following readings were obtained on

single frequency transients

a. Time to reach the peak re striking voltage - 50µ sec

b. The peak re striking voltage, 100 kV

what will be the frequency of oscillations?

a. 100 Hz

b. 1,000 Hz

c. 10,000 Hz

d. 10 Hz

ANSWER: 10,000 Hz

15) For the following figure shows a CB circuit with L - C introducing a damping circuit.

For the critical damping what is the value of r?

a. √(LC)

b. 0.5*√(C/L)

c. 0.5*√(L/C)

d. 2π*√(L/C)

ANSWER: 0.5*√(L/C)

Power System Objective TypeQuestions With Answer

Publisher : Faculty Notes Author : Panel Of Experts

Type the URL : http://www.kopykitab.com/product/11117

Get this eBook

50%OFF