Power Factor Equations

Power factor measures the phase angle between the instantaneous voltage and the instantaneous current in a circuit. Voltage (E) leads current (I) by 90° in an inductive (L) circuit and voltage (E) lags current (I) by 90° in a capacitive (C) circuit.

A popular mnemonic is ELI the ICE man since E is leading (coming before) I in ELI, and E is lagging (coming after) I in ICE.

 

power factor ( Pf ) = cos ( q )
Apparent Power ( P ) = I * V
True Power = P
I = Current
q = Phase angle
V = Voltage

 

Power Formulas
Apparent Power P = I * V P = I2 * R P = V2 / R	True Power P = I * V * cos (q) P = I2 * Z * cos (q) P = V2 * cos (q) / Z P = Pa * Pf	Impedance Z = V2 * cos (q) / P Z = P / [I2 * cos (q)]
Current I = P / [V * cos (q)] I = sqrt {P / [Z * cos (q)]}	Voltage V = P / [I * cos (q)] V = sqrt [P * Z / cos (q)]
where P = power in Watts V = Voltage in Volts I = current in Amps R = resistance in Ohms (Ω) Z = impedance in Ohms (Ω) q = phase angle between I and V in degrees Pa = apparent power in Volt·Amps (VA) Pf = power factor

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