Distribution Transformer Load Characteristics

To obtain fundamental information concerning distribution transformer load characteristics, a major study was undertaken by the General Electric Company, together with 55 electric utility companies. Monthly readings of load data were obtained in the field, using especially designed test kits installed at distribution transformers serving predominantly residential loads. Significant results, in terms of national average annual data, are summarized in percentages as: power factor, 92.5; load factor, 26.6; loss factor, 10.5; and peak load, 13.2. Load and loss factors are lower than previously estimated; power factors are higher. Values of the standard deviation associated with each of the averages were calculated. It is significant that, for the first time, a degree-of-uncertainty factor associated with load characteristics and with calculations based on load characteristics has been identified on the basis of statistical analysis. The information derived should be useful to the electric industry because it provides greater knowledge of the most fundamental component of the electric system, i.e., the load itself.