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AC Power

Apparent Power, S - appears on the hypotenuse of the power triangle.

Apparent power is given by:

Apparent power = V I

= Voltage * Current

Units are volt -amps (VA)

True Power, P - appears on the adjacent of the power triangle

True power is given by:

I2R = S cos f = VI cos f

This is the power in the resistive part of the circuit

Units are Watts (W)

Reactive Power, Q - appears on the opposite of the power triangle

Given by:

I2XL = S sin f = VI sin f

and: I2XC = S sin f = VI sin f

where XL and XC are inductive reactance and capacitive reactance respectively, and f is the phase angle.

Units are volt-amps reactive (VAr)

Power Factor:

Power Factor = True Power / Apparent Power = P / S = cos f

True Power  = Apparent Power * Power Factor

= VI cos f

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