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