Thermal analysis and derating of a power transformer with harmonic loads

Thermal conditions of power transformers in abnormal operating conditions such as harmonic loads can be considered as a critical case. In this study, thermal analysis of transformer and additional imposed heat on it, caused by non‐linear loads, are addressed. For this purpose, an appropriate thermal equivalent circuit is used in which temperature of different parts of oil‐immersed power transformers are obtained for harmonic loads. The losses of various components of transformer as heat‐generating sources are estimated. At this end, an appropriate three‐dimensional finite element method is applied to estimate the losses of different parts of transformer. To keep the transformer temperature rise around the permissible value, the transformer is derated. Transformer derating based on the IEEE Std C57.110–2008 recommendation considerably reduces the transformer loading capability. Therefore, this study introduces a new technique for derating of transformer for harmonic loads. This enhances the transformer thermal limits and transformer loading capacity.