Switchgear Protections

51. Resistance grounding is used for voltage between

1. 33kVto66kV
2. HkVto33kV
3. 3.3kVandllkV
4. none of the above

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52. Series capacitors are used to

1. compensate for line inductive reactance
2. compensate for line capacitive reactance
3. improve line voltage
4. none of the above

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53. Series reactors should have

1. low resistance
2. high resistance
3. low impedance
4. high impedance

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54. SF6 gas

1. is yellow in colour
2. is lighter than air
3. is nontoxic
4. has pungent small
5. none of the above

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55. Short-circuit currents are due to

1. single phase to ground faults
2. phase to phase faults
3. two phase to ground faults
4. three phase faults
5. any of these

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56. Shunt capacitance is neglected while considering

1. short transmission line
2. medium transmission line
3. long transmission line
4. medium and long transmission lines

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57. The arc voltage produced in A.C. circuit breaker is always

1. in phase with the arc current
2. lagging the arc current by 90″
3. leading the arc current by 90°
4. none of the above

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58. The arcing contacts in a circuit breaker are made of

1. copper tungsten alloy
2. porcelain
3. electrolytic copper
4. aluminium alloy

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59. The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to

1. lubricate the contacts
2. insulate the contacts from switch body
3. extinguish the arc
4. all of the above

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60. The current zero interruption, in oil and air blast circuit breakers, is achieved by

1. lengthening of the gap
2. cooling and blast effect
3. both (a) and (b)
4. deionizing the oil with forced air
5. none of the above

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