Explain why 3 phase induction motor at no load operates at a very low power factor?

Answer 1

An induction motor electrically appears much like an inductor with a resistive component. The resistive component is reflective of the mechanical power which the motor delivers. There are also some true resistive losses in the motor widings, but these are relatively smalll. At no load both these contribute to the total electrical resistive component of the IM. The resistive component at no load however will be small compared to the IM's inductance, resulting in a very low power factor. As the mechanical load on the motor is increased its effective electrical resistive component increases and so does its power factor.

Another way of thinking about this is that a circuit's power factor is indicative of its electrical resistance, which dissipates watts. At no load very little actual electrical power (watts) is required to rotate the IM, so its power factor is low. If the IM is driving a large mechanical load more actual power must be delivered to the IM and this is indicated by a much larger power factor.

_____

Under no load slip is almost zero, i.e.. there is almost no induced current in the inner coil. So power factor which is induced power to input power ratio is small.

As load increases, slip increases for a given motor and so does the induced current and the torque generated in turn to run the load.

Answer 2

At no load the magnetising component of current is more as compared with a transformer, because of air gap between stator and rotor,