determine input/output power with a twist

Thread Starter


Joined Mar 1, 2010

I have a question. Please I am not looking for the answere. I realy want basic simple steps/maths equations.

Ok... I know power-in = √3 x Vl x Il x pf

I have 400v, 50Hz, full load speed of 960rpm, draws 22amps and power factor of .088... I worked the input power as follows, correct me if I am wrong or point me in the right direction...

input power = √3 x 400 x 22 x 0.88 = 13413Kva

The question however says to calculate the input power if the motor has an efficiency of 90%... this is what is confusing me... how do I work out the 90% part?

Many Thanks


Joined Mar 6, 2009
You are right - the question (as you recall it) regarding efficiency makes no sense.

The efficiency would relate motor mechanical output [shaft] power to the electrical input power.

BTW your answer is confusing in terms of the units shown.

Power = 13.413 kW.