Motor Power Factor

A motor power factor will change based on the loading of that motor. The amount of energy that is stored and released in the motor's magnetic field with each sine wave is constant, regardless of its load. This is called the Reactive Load or Reactive Amps.

Since we previously learned about the Power Factor Triangle, this concept will be easy.

Ideally the current flow of a motor running with no load connected (the no-load current), is also the magnetizing current, or reactive current. In reality, a very small amount of real power is used to overcome friction and windage while spinning the motor at no-load.

With the motor running only slightly loaded, the motor power factor is poor due to a high ratio of magnetizing current to load current. However, as the motor gets loaded and its load current increases, its power factor improves.


Also, if the motor is oversized or improperly designed, the magnetic field is oversized relative to the load, and the motor power factor is worse than if properly sized. This can occur in 2-speed motors whereby the physical design of the motor lends itself more to the high speed mode than the low. In this case the low speed winding can actually have a higher magnetizing current than the high speed winding, making the low speed motor's power factor considerably worse.