Power Triangle:

Within AC circuits, current and voltage are generally out of phase and, as a conclusion, not all the power produced through the generator could be used to accomplish work.  Through the similar token, power cannot be calculated in AC circuits in the similar manner as in DC circuits.  The power triangle, display in Figure, equates AC power to DC power through showing the relationship among generator output (apparent power - S) in volt-amperes (VA), usable power (true power - P) in watts, and wasted or stored power (reactive power - Q) in volt-amperes-reactive (VAR).  The phase angle (θ) represents the inefficiency of the AC circuit and corresponds to the overall reactive impedance (Z) to the current flow in the circuit.

Figure: Power Triangle

The power triangle represents comparable values that can be used directly to find the efficiency level of generated power to usable power that is expressed as the power factor. Reactive power, apparent power, and true power could be calculated through using the DC equivalent (RMS value) of the AC voltage and current components along with the power factor.