78. A reactance relay is
A. voltage restrained directional relay.
B. directional restrained over-current relay.
C. voltage restrained over-current relay.
D. none of these

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79. To limit current chopping in vacuum circuit breakers, the contact material used has
A. high vapour pressure and low conductivity properties.
B. high vapour pressure and high conductivity properties.
C. low vapour pressure and high conductivity properties.
D. low vapour pressure and low conductivity properties.

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80. Rate of rise of restriking voltage depends
A. type of circuit breaker.
B. inductance of the system only.
C. capacitance of the system only.
D. inductance and capacitance of the system.

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81. If the fault current is 2000 amps, the relay setting 50% and the C.T. ratio is 400/5, then the plug setting multiplier will be
A. 25 amps
B. 45 amps
C. 50 amps
D. none of these

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82. A large-size alternator is protected against overloads by providing
A. overcurrent relays.
B. temperature sensitive relays.
C. thermal relays.
D. none of these

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83. A 50 Hz, four,pole turboalternator rated at 20 MVA, 43.2 kV has an inertia constant H = 4 kW sec/kVA. The K.E. stored in the rotor at synchronous speed is
A. 80 kilojoules
B. 80 megajoules
C. 40 megajoules
D. 20 megajoules

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84. If Pm is the maximum power transferred, the loss on the system is Pm
A. mc
B. ?2 m
C. 3Pm
D. none of these

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