Thermal evaluation of a medium frequency transformer in a line side conversion system

A central part of a medium frequency conversion system is the transformer. A medium frequency transformer for railway propulsion may be stressed beyond 30 kV with voltage slopes around 50 kV/mus depending on topology while the geometric dimensions are small. A 170 kVA transformer prototype operated at 4 kHz has been developed and tested. A transient thermal model of the transformer is developed and verified experimentally. The transient thermal behavior is important in propulsion applications where the conversion system is often heavily overloaded. Simulations indicate that the overloading capability of the transformer is comparable to a conventional traction transformer. Experimental results are in good agreement with the model.