The no load current of a SQ induction motor as a thumb rule can be assumed to be around 30 to 40% of full load amps. It means the motor consumes 30 to 40% of full power in no load condition. So a 15kw motor will consume around 5kw power when run in no load condition. Is it correct?

Now running the same motor with 50% speed with help of drive in no load condition. Assuming the current almost constant in lower speed and reduced voltage, will the power also be halved?

or something else? considering same IR losses due to same current and less friction and windage losses?

 

Praveen... your assumption is incorrect:

The relationship between no-load current and no-load power is not linear. No-load power is based only on stator-winding loss at no-load, excitation-loss, friction, windage, and stray losses. For example, for a 15kW motor, the no-load loss is about 0.5kW.

Regards, Phil Corso

 

do you mean that 15 kw motor on no load condition will consume only .5kw power?

 

Also the power factor goes to hell, so the ratio of reactive and real power will change dramatically.