Measurement of harmonic losses of pole transformers and single-phase induction motors

A computer-aided testing circuit is used to accurately measure the effects of harmonic voltages on the losses of transformers and motors. The computer samples 361 times during one fundamental cycle (60 Hz) and performs a Fourier analysis on the data to determine harmonic losses. The testing circuit is calibrated by sampling a sinusoidal voltage and current and comparing the values read by the computer to values read by digital meters. Tests were performed on 1 kVA and 25 kVA single-phase transformers at varying loads and a 2 hp single-phase induction motor with different values of run capacitance. For both transformers and motor, losses were measured with the 3rd through 13th odd voltage harmonics superimposed upon the fundamental voltage. Induction machine losses were measured by sampling the input voltage and current, and subtracting the output power which was measured with a torquemeter. Transformer losses were measured using both an accurate and approximate method. The accurate method requires a power amplifier rated as high as the transformers (25 kVA for the 25 kVA transformer), but the approximate method only requires a rating equal to the worst case iron-core losses at rated voltage (78 W for the 25 kVA transformer)