AC Power

Real, reactive and apparent power — the power triangle and why power factor matters.

Easy

Power	Symbol	Unit	Formula
Real (active)	$P$	W	$VI\cos\phi$
Reactive	$Q$	var	$VI\sin\phi$
Apparent	$S$	VA	$VI$

$S = P + jQ = \mathbf{V}\mathbf{I}^* \qquad |S|^2 = P^2 + Q^2$

Real power does useful work; reactive power sloshes back and forth between source and the magnetic/electric fields of the load. Cables, transformers and generators must carry the full apparent power, which is why utilities care about power factor.

Sub-topics (2)

Power Factor

Power factor is the ratio of real to apparent power — low PF wastes capacity and raises losses.

Easy♥ 0🔖 0💬 0

Power Factor Correction

Add capacitors (or active circuits) to cancel lagging reactive power and raise the power factor.

Intermediate♥ 0🔖 0💬 0

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Sub-topics (2)

Power Factor

Power Factor Correction

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