Typical power factor versus load curve bands for 2- and 4-pole three-phase, cage-induction motors
The total motor load in a facility is usually a major factor in determining the system power factor. Low system power factor results in increased losses in the distribution system. Induction motors inherently cause a lagging system power factor. The power factor of an induction motor decreases as the load decreases. Rated-load power factor increases with an increase in the power rating of the motor. A number of induction motors, all operating at light load, can cause the electrical system to have a low power factor. The power factor of induction motors at rated load is lower for low-speed motors than for high-speed motors.
A small increase in voltage (less than 10 percent) above rated voltage will decrease the power factor, and a small decrease in voltage (less than 10 percent) below rated voltage will improve the power factor of an induction motor. However, other performance characteristics may be adversely affected by such a change in voltage and operation as close as possible to the rating-plate voltage and power rating is recommended.