The effect of output isolation requirements on traction converter design

Static converters for use in traction applications are commonly required to produce an AC output for driving air conditioning, blower and catering loads and a DC output for battery charging and other loads such as lighting and safety related circuitry. The converter outputs, both AC and DC, have typically been derived via an output transformer to provide galvanic isolation between converter input and output; galvanic isolation being a specific requirement of most rail operators. Galvanic isolation physically decouples the coach auxiliaries from the high voltage AC or DC track supply and protects the coach builder and rail operator from the potentially harmful effects of these and other converter derived voltages. The author, through the example of a typical static power converter, examines the possible impact of the removal of output isolation particularly with respect to converter power dissipation, weight, and cost