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For the following questions answer them individually
The synchronous speedof a four-pole induction motor operating at 50Hz is
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?
Decrease to 160 ohm
Remains the same at 200 ohm
Increases to 250 ohm
Increases to 312.5 ohm
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
Frequency corresponding to rotor speed
When the supply voltage to an induction motoris reduced by 10%, the maximum torque decreased by approximately
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
The injected e.m.f in the rotor of an induction motoris of
The same frequencyas slip frequency
The same phase as the rotor e.m.f
A high value for satisfactory speed control
The same phase as rotor e.m.f and a high value for satisfactory speed control.
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?
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
Be reduced by 10%
Be increased by 10%
Be reducedor increased by 20%
The speed of an induction motoris controlled by varying the supply frequency keeping V/f constant, then
Breakdown torque and magnetizing current would both remain constant
Breakdown torque would remain constant but magnetizing current would increase.
Breakdown torque would decrease but magnetizing current would remain constant.
Breakdown torque and magnetizing current both would decrease.
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
none of these
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