Basic Formula to Calculate Apparent Power in Single and Three Phase Circuits

Apparent power is defined as the product of current time voltage passing through an AC circuit.

The basic formula to calculate apparent power in any circuit is:
S = VI
where S = Apparent power measured in VA (volt-amperes)
V = Voltage
I = Current

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Industrial unit

Unit VA is very small for heavy equipment and practically kVA is used instead of  VA.

Where S (kVA) = VI / 1000

In single and three phase circuit the kVA formulas are:

Single phase kVA = [V * I] / 1000

Three phase kVA = [E * I * 1.73] / 1000

Example 1: Find the apparent power in kVA drawn by a 200 V single phase generator having 2 Amps current passing through it.

Solution: kVA = 200 * 2 / 1000 = 0.4 kVA

Example 2: Find the current drawn by 500 kVA transformer @ rated voltage 5 kV.

Solution: By cross multiplication:

I = (500 * 1000) / (1.732 * 5k) = 57.73 Amps

Other useful formulas:

1. Amps from HP
2. Amps from kW
3. Amps from kVA
4. Angular velocity
5. Angular acceleration