Electronics and Communication Engineering - Power Electronics - Discussion


A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be

[A]. about 1350 rpm
[B]. about 720 rpm
[C]. about 360 rpm
[D]. either (b) or (c)

Answer: Option B


In this case synchronous speed at 50 Hz is 1500 rpm. Therefore synchronous speed at 25 Hz is 750 rpm. Since slip is about 3 - 5%, speed is about 720 rpm.

Mahendra said: (Nov 8, 2016)  
I think it must be 690 rpm.

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