1.

A 3-phase, 400V, synchronous motor is providing load at 0.8 p.f. lagging. If the field current of the motor is continuously increased, then the _____________(a) power factor increases and then decreases(b) power factor is not affected(c) power factor decreases upto a certain value of field current and then increases(d) power facor increases simplyI got this question in an interview for job.This intriguing question originated from Starting of Synchronous Motors in section Synchronous Motors of Electrical Machines

Answer»

Right answer is (a) power FACTOR increases and then decreases

For EXPLANATION I WOULD SAY: The magnetization current is increased as we INCREASE the excitation, so the power factor will increase upto the saturation and then again it will decrease.



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