Special transformers arrangement for AC railway systems

This paper deals with special transformer connections for mitigating the current and voltage unbalances generated by single-phase AC traction loads, as typically occurs for electric high speed railway loads supplied by the three phase power system. In fact they represent one of the main sources of power quality perturbation of the grid, with consequent denigration of its performance. The current unbalance reduces efficiency, productivity and profits at the generation, transmission and distribution of electric energy. Voltage asymmetry reduces efficiency, productivity and profits at the consumption and utilization level. Transformer connections for mitigating these perturbations are summarized and compared each other. These mainly consist on different types of connections of single-phase transformers of the substation to the three-phase primary section with phase-transformation methods. Finally, an advanced scheme for current balancing and power factor improving of two unbalanced loads is performed.