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.