How to calculate the field efficiency of running motors when you don't have the no load & locked rotor test results?

The only information that I have are the input power, the nameplate rating (kW), the shaft rpm, the shaft dia.

 

Sayan... measure its temperature-rise above ambient. Then compute its output power, kWout, which will be proportional to temp-rise divided by its rated-rise over a specified ambient, say 40 Deg C!

Finally, divide kWout by the input power you already have, kWin.

A second method to determine temperature-rise is by measuring the change in winding-resistance from "cold" (ambient) to "hot" (at operating load).

Regards, Phil Corso

 

Sayan... the following archived Control.Com threads contain formulas you can use. One of them also discusses using slip-measurement:

http://www.control.com/thread/1026163908

http://www.control.com/thread/1026164342

http://www.control.com/thread/1026185658

Regards, Phil Corso (cepsicon[at]aol[dot]com)