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Apparent Power

Friday, April 06, 2018

Apparent PowerWhen using a nonlinear AC powered device it can affect the current or voltage waveform in the AC power signal. Equipment with capacitive components will resist change in voltage, which has the affect of retarding the voltage wave such that it is lagging the current wave. Units that have inductive components will result in the current phase lagging the voltage waveform.

Whenever the voltage is not in phase with the current the simple power equation….

P = I.V

is no longer valid. The apparent power (VA) is the Pythagorean Theorem sum of the reactive power and the active power. The active power (W) is what we would commonly know as power, or the linear power, that the unit actually uses. The reactive power (VAR) is the unused power which is generated by the current and voltage that is out of phase. This is not consumed by the appliance, but still must be supplied by the mains source. The ratio of active power to reactive power is called the power factor or “Cos ϕ”.

Distribution Network Operators (DNOs) have restrictions to commercial and industrial users that specify the limits of power factor that the user must adhere to. The sum of reactive power is recorded on commercial electric meters such that if these limits are exceeded the user is fined by the DNO.

 


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