Traction transformers for fixed installation used along the track for the supply of power to the overhead contact line, directly (AC traction systems) or through static converters (DC traction systems).
Most commonly AC traction systems are supplied by single-phase transformers with primary winding connected between two phases of HV grid and secondary winding connected to the overhead contact line and to the rail.
The main features of railway transformer operation are non-continuous and cyclic load with frequent overloads, which can be up to several times greater than rated load.
A traction transformer in service is exposed to frequent inrush currents and short-circuits.
Therefore the mechanical strength of windings and complete active part in respect to forces produced by over-currents is of great importance for reliable operation of traction transformer.