apparent power

Apparent power is a measure of alternating current (AC) power that is computed by multiplying the root-mean-square (rms) current by the root-mean-square voltage. In a direct current (DC) circuit, or in an AC circuit whose impedance is a pure resistance, the voltage and current are in phase, and the following formula holds:

P = E_rmsI_rms

where P is the power in watts, E_rms is the root-mean-square (rms) voltage in volts, and I_rms is the rms current in amperes. But in an AC circuit whose impedance consists of reactance as well as resistance, the voltage and current are not in phase. This complicates the determination of power.

In an AC circuit, the product of the rms voltage and the rms current is called apparent power. When the impedance is a pure resistance, the apparent power is the same as the true power. But when reactance exists, the apparent power is greater than the true power. The vector difference between the apparent and true power is called reactive power.

If P_a represents the apparent power in a complex AC circuit, P_t represents the true power, and P_r represents the reactive power, then the following equation holds:

P_a² = P_t² + P_r²

Do you have something to add to this definition? Let us know. Send your comments to techterms@whatis.com

Digg This!     StumbleUpon     Del.icio.us