Assessment of Effect of Load Models on Loss-of-Life Calculation of a Transformer Using a Point Estimation Method

Abstract

The study of the impact of load models on transformer insulation life is essential for the truthful aging calculation. In most of the studies related to the assessment of transformer aging, distribution loads are treated as constant power type. However, the practical loads are of mix type (combination of constant power, constant current, constant impedance). Moreover, the residential, commercial, and industrial loads comprise the different percentages of constant power, constant current, and constant impedance loads. In this article, different load models are investigated to quantify their impact on the aging calculation of a transformer under various loading scenarios and environmental conditions. The study includes different classes of the loads with corresponding load shapes, ambient temperatures, determined for a typical week of each season. It considers highly unbalanced transformer loading conditions and network configurations. The study also considers the effect of harmonics on the transformer aging. Aging acceleration rate and percentage loss of life of the substation transformer connected to IEEE 13-bus system have been calculated for different loading and climatic conditions. The same procedure has been adopted for the modified IEEE 123-bus system, and the trends of the results have been compared with the IEEE 13-bus system. It has been shown that the load models make a considerable effect on life calculation of a transformer. Therefore, selection of an appropriate load model is important for accurate estimation of aging of a transformer.