Explain the terms real power, apparent power and reactive power for ac circuits and also the units used.

Explanation of terms real power, apparent power and reactive power for AC circuits:

Diagram: Power triangle relating apparent power to true power and reactive power.

Definition	Real Power	Apparent power	Reactive Power
	It is the product of voltage, current and power factor.	It is the product of voltage and current.	It is the product of voltage, current and sine of angle between the voltage and current.
Unit	Basic unit of real power is watt. i.e. Expressed as W or kW.	Basic unit of apparent power is volt- ampere. Expressed as VA (Volt Ampere) or KVA.	Has no other unit but expressed in VAR (Volt Ampere Reactive) or KVAR.
Formulas	Real power (P) = V I                                  (In DC circuits) P = VI Cosθ                         (in Single phase AC Circuits) P = √3 VL IL Cosθ         or P = 3 VPhIPh Cosθ (in Three Phase AC Circuits)	Apparent power (S) = V I Apparent Power = √ (True power2 + Reactive Power2) KVA = √KW2 + KVAR2	Reactive power (Q) = V I Sinθ Q =√ (Apparent Power2– True power2) VAR =√ (VA2 – P2) KVAR = √ (KVA2 – KW2)

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