This test is performed to determine no-load current I0, no-load power factor cos Ø0, windage and friction losses, no-load core loss, no-load input, and no-load resistance R0 and reactance X0. This test is performed with different values of applied voltage below and above rated voltage while the motor is running light (without load).
At no-load the machine runs at very small slip sufficient to provide power for windage and friction loss, core loss and also a certain amount of stator copper loss, which has to be, accounted for because of the large no load current.With low slip, the following approximation will hold good.
R2’(1/s-1) is very high
With these approximations the necessary formulae for finding out Xm will be given while conducting the no-load test.