Question

How is apparent power calculated in a three-phase circuit?

Answer 1

Apparent power (S) in a three-phase circuit is calculated using the formula:


=

rms
×

rms
S=V
rms
    ​

×I
rms
    ​


Where:


rms
V
rms
    ​

 is the root mean square (RMS) voltage of the circuit.

rms
I
rms
    ​

 is the root mean square (RMS) current of the circuit.

For a balanced three-phase circuit, the formula simplifies further:


=
3
×

rms
×

rms
S=
3
    ​

×V
rms
    ​

×I
rms
    ​


Where the factor of
3
3
    ​

 comes from the trigonometric relationships between the phase voltages and phase currents in a balanced three-phase system.

The apparent power represents the total power, including both the real power (which performs useful work) and the reactive power (which is responsible for establishing the magnetic fields in inductive elements and electric fields in capacitive elements). The unit of apparent power is volt-amperes (VA) or kilovolt-amperes (kVA) in the case of larger power systems.

In summary, to calculate apparent power in a three-phase circuit, you need to know the RMS voltage and RMS current values, and then use the appropriate formula depending on whether the circuit is balanced or not.