Numerical Study of the Core Saturation Influence on the Winding Losses of Traction Transformers

The winding system of traction transformers is subjected to non-sinusoidal voltages and currents of the adjacent traction converter. Unlike its fundamental component, the higher harmonics of the load current have a completely non-uniform distribution over the conductor's cross section causing hazardous hot spots. Due to dynamic operating conditions in railway grids, the railway voltage can temporarily increase as much as 20% saturating magnetic cores of traction transformers. This paper presents the analysis of the core saturation influence on the distribution of the transformer's winding losses along with suitable numerical methodologies for their simulation. Thus, a fast 2-D and 3-D frequency-domain methodology for computing winding losses of traction transformers by considering all the relevant higher current harmonics and core saturation effects caused by the fundamental voltage component is described in detail. The obtained results are verified by comparison against the available corresponding measurements and against the results of a rigorous and from the CPU time perspective much more demanding time-domain simulation approach.