Load Power Factor and Power Factor Limitation

Devices like transformers and motors require power to maintain magnetic fields to perform their function. This so called “reactive” (kVAR) power flows into and out of the device but is not really consumed to perform work. The power that is consumed is called the “real” (KW) power and the vector sum of reactive and real power is called the “apparent” (kVA) power. Power factor (PF) is the ratio of real power to apparent power. The terms “leading” and “lagging” refer to reactive power being put in or taken out by the device.

In the real world, leading power factors are rare. For individual devices, lagging power factors can typically range from 0.4 to 0.99. With respect to power conditioners, a limitation on load power factor is generally required if the unit will not operate or respond properly if the power factor is too low. Unless the power factor of the existing or future devices to be protected are well known, it is best to select power conditioners with no (or minimal) load power factor limitations.