At first, let's define the following variables:
P: Power;
U: DC Voltage, I: DC Current;
Ua, Ub, Uc: AC Voltage of Phase to Neutral;
Uab, Ubc, Uca: AC Voltage of Phase to Phase;
Ia, Ib, Ic: AC Current on each phase;
Cosφ: Power Factor.
As we know, in a symmetrical three phase circuit
Uab = Ubc = Uca =√3Ua =√3Ub =√3Uc;
Case 1, DC circuit:
P = U * I
Case 2.1, AC single phase circuit:
P = Ua * Ia * Cosφ
Case 2.21, AC symmetrical three phase circuit:
P = 3 * Ua * Ia * Cosφ = √3 * Uab * Ia * Cosφ
Case 2.22, AC asymmetrical three phase circuit:
We need to calculate the power of each of the three phase circuits separately, and then sum them up
Tips:
The motor power factor can be estimated in this way
Synchronous Motor: Around 0.91
Asynchronous Motor: 0.7 ~ 0.85
