ISRO Scientist or Engineer Electrical 2013

Instructions

For the following questions answer them individually

Question 31

The synchronous speedof a four-pole induction motor operating at 50Hz is

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Question 32

A shunt generator has a critical field resistance of 200 ohm at a speed of 800r.p.m. If the speed of the generator is increased to 1000r.p.m., what is the change in critical field resistance of the generator?

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Question 33

A three-phase slip ring induction motor is fed from the rotor side with stator winding short circuited. The frequency of currents flowing in short circuited stator is

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Question 34

When the supply voltage to an induction motoris reduced by 10%, the maximum torque decreased by approximately

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Question 35

A 3-phase induction motor is driving full-load torque which is independent of speed. If line voltage drops to 90% of the rated value, percentage increase in motor copper losses

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Question 36

The injected e.m.f in the rotor of an induction motoris of

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Question 37

If the full-load speed of a 3-phase, 50Hz induction motor is 950 r.p.m, what is its half load speed nearly equal to?

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Question 38

For controlling the speed of an induction motor the frequency of supply is increased by 10%. For magnetizing current to remain the same, the supply voltage must

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Question 39

The speed of an induction motoris controlled by varying the supply frequency keeping V/f constant, then

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Question 40

A synchronous generator connected to an infinite bus is overexcited. Consider the only reactive power, from the point of view of the system, the machine acts as

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