how to calculate efficiency of three phase transformer?

To calculate the efficiency of a three-phase transformer, use the formula: Efficiency (?) = (Output Power / Input Power) � 100%. First, measure the output power by multiplying the output voltage, current, and the square root of three (for three-phase systems). Then, determine the input power by measuring the input voltage and current. Subtract losses (copper and iron losses) from the input power to get the effective input power before calculating efficiency.