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Article Date: 17th August 2018

Advanced - What is Power Factor?

Power Factor - AC Circuits - Diesel Generators - Generator Sets

Advanced - What is Power Factor

In its simplest form, Power Factor is the ratio of kW to kVA. Note that Power Factor is only relevant in AC circuits. As a result, the Power Factor of a circuit will always be a number between 0 and 1, and is usually to 1 or 2 decimal places.

Power Factor can also be represented by thinking of a simple clock face, where a PF of 1 is represented by 12 o’clock. A PF of 0 can be either side of 12, either at 9 or 3 o’clock (depending on which way the kVArs are flowing in reference to the kW). The number isn’t signed and is usually accompanied by leading or lagging. i.e. the current is leading or lagging the voltage. PF is caused by kVArs which are signed. When a generator is producing (positive) kVArs the load is inductive, such as a motor, and thus the current is lagging the voltage. Terms used to explain this are inductive, lagging and over excitation. When a generator is absorbing (Negative) kVArs the load is capacitive such as fluorescent lighting and long cable runs, and thus the current is leading the voltage. Terms used to explain this are capacitive, leading and under excitation.

If the generator is feeding a purely resistive load, such as a heating element, there are no kVArs, and the PF is 1, also known as unity. This is when kW (real power) is equal to kVA (apparent power).

Power Factor Formula
PF can be calculated using the following formula: PF = kW / kVA

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