how to calculate power factor of transformer?

To calculate the power factor of a transformer, you need to determine the real power (P) in watts and the apparent power (S) in volt-amperes (VA). The power factor (PF) is then calculated using the formula: PF = P / S. Measure the real power using a wattmeter and the apparent power can be calculated by multiplying the voltage (V) and current (I) on the transformer’s primary or secondary side: S = V � I.