Distribution Transformer No-Load Losses

The no-load losses measured during the test are assumed to consist essentially of core losses, i.e., hysteresis and eddy current losses. Eddy current losses deduced from experiments are generally higher than those calculated from the classical theory. The difference between these two quantities is called the ``anomalous'' loss. A brief review of these losses is given, although in most of the analyses the no-load losses are assumed to consist of hysteresis and eddy current losses. The calculation of losses in magnetic materials for distorted flux waveforms is rather complex. Several attempts have been made in recent years to convert the losses measured under non-sinusoidal excitation conditions to a common base of losses under sinusoidal excitation conditions. A brief review of the work done by previous investigators and the correction methods they proposed are given. The effect of temperature on no-load losses is illustrated through two sets of experiments. In the first set, hysteresis loss and total loss on Epstein samples of 12 mil RGO and HGO steels were obtained as a function of temperature in the range of 20??C to 200??C. The results showed that hysteresis loss is constant with temperature, and eddy current loss decreased with increasing temperature. In the other set, no-load losses of a number of distribution transformers, ranging in size from 10 through 50 KVA, were measured in the temperature range of 20??C to 100??C. The results showed that the losses decreased with increasing temperature. Results for both sets of experiments are illustrated in Fig. 1.