Switchgear Protections

81. The voltage appearing across the contacts after opening of the circuit breaker is called _________ voltage.

1. recovery
2. surge
3. operating
4. arc
5. none of the above

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82. Thermal circuit breaker has

1. delayed trip action
2. instantaneous trip action
3. both of the above
4. none of the above

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83. Thermal overload relays are used to protect the motor against over current due to

1. short-circuits
2. heavy loads
3. grounds
4. all of the above

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84. To protect most of the electrical equipment handling low power, the types of relays used are

1. thermocouple
2. electronic and bimetallic
3. both (a) and (b)
4. none of the above

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85. To reduce short circuit fault currents are used.

1. reactors
2. resistors
3. capacitors
4. none of the above

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86. transmission line has reflection coefficient as one.

1. Open circuit
2. Short-circuit
3. Long
4. None of the above

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87. Ungrounded neutral transmission system is not recommended because of system

1. insulation being overstressed due to over voltages
2. insulation overstress may lead to failure and subsequent phase to phase faults
3. being inadequately protected against ground fault
4. all of the above

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88. Wave trap is used to trap waves of

1. power frequencies
2. higher frequencies entering generator or transformer units
3. either of the above
4. none of the above

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89. What will be the reflection co-efficient of the wave of load connected to transmission line if surge impedance of the line is equal to load?

1. Zero
2. Unity
3. Infinity
4. None of the above

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90. When a transmission line is energized, the wave that propagates on it is

1. current wave only
2. voltage wave only
3. both (a) and (b)
4. power factor wave only

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