Power transformers life expectancy under distorting power electronic loads

The proliferation of nonlinear loads causes harmonic voltage distortion on public and industrial networks. The transformer´s thermal loss of life, estimated for sinusoidal loads, can be slightly reduced if we consider the harmonic currents. In this paper we study a distribution transformer (630 kVA) loss of life, driving a load cycle including a sinusoidal load and a weighted distorting one. The transformer thermal and electrical models are presented and the simulation results are analyzed. We propose a general expression to characterize loss of life derating; this expression includes only the current total harmonic distortion and two transformer specific parameters