Induction motors present a lagging (inductive) power factor to the power line.The power factor in large fully loaded high speed motors can be as favorable as 90% for large high speed motors. At 3/4 full load the largest high speed motor power factor can be 92%. The power factor for small low speed motors can be as low as 50%. At starting, the power factor can be in the range of 10% to 25%, rising as the rotor achieves speed.
Power factor (PF) varies considerably with the motor mechanical load (Figure below). An unloaded motor is analogous to a transformer with no resistive load on the secondary. Little resistance is reflected from the secondary (rotor) to the primary (stator). Thus the power line sees a reactive load, as low as 10% PF. As the rotor is loaded an increasing resistive component is reflected from rotor to stator, increasing the power factor.
The graph below illustrates Induction motor power factor and efficiency.
![](https://i0.wp.com/www.electricalengineering.xyz/wp-content/uploads/2020/10/induction-motor-power-factor-and-efficiency-curve.png?resize=540%2C150&ssl=1)
Article extracted from: Lesson in Electric Circuits AC Volume Tony R Kuphaldt under Design Science License.