HARMONICS EFFECT ON THE THERMAL PERFORMANCE OF THE DISTRIBUTION TRANSFORMERS AND HOW TO MITIGATE IT

Abstract

This thesis focuses on the effect of harmonic distortion on distribution transformers operating near the thermal limit and the ways of mitigating the harmonics effect. The theory of harmonics, its sources, and its effects are studied, a thermal model to predict a transformer hot spot temperature and thermal ageing acceleration factor under non-linear conditions is presented, and the mitigation of the harmonic effect is discussed. It has been focused on distribution transformers due to the high numbers of failures nationally and internationally attributed to unknown causes. A transformer thermal model is presented through theoretical considerations. Finally, a case study is presented on the loading capability of a transformer under non-linear conditions. The main effect of non-sinusoidal current on distribution transformers is an increase in the transformer losses that lead to a temperature rise of the distribution transformer. The increased heat can lead to failure of insulation, which can reduce the transformer's life and cause eventual breakdown. The transformer load losses are ohmic losses, winding eddy current losses and other stray losses. This harmonics effect on transformer losses is modeled