Simulation of traction electricity supply systems equipped with unbalance-to-balance transformers

One-phase tractive loads of AC railways result in a significant unbalance in the three-phase supply main. To reduce it, three types of transformer connection phasing are used at traction substations. For supply electric power systems with a short-circuit capacity less than 1000 MV· A, this phasing doesn't produce a meaningful effect. Unbalance can be eliminated on the basis of unbalance-to-balance transformers, but calculation methods of traction power system modes with this kind of transformers are virtually non-existent. The article considers the issues of modeling traction power supply systems equipped with unbalance-to-balance transformers based on the methods developed in Irkutsk State Transport University. It analyzes the effectiveness of application of unbalance-to-balance Woodbridge, Kuebler, Le Blanc transformers, and also four-winding transformers. The positive effect of the unbalance-to-balance transformer depends on the ratio of power supply arm loads, that is, on the power consumption of trains and their traffic schedule. The maximum effect takes place with commensurable volumes of train traffic with an identical current profile on either side of the substation with the unbalance-to-balance transformer. To implement this situation, idealized current profiles and traffic schedule were used in the modeling. The computer modeling results based on the Fazonord software package are indicative of a sufficiently high effectiveness of application of unbalance-to-balance transformers. The sufficient reduction of voltage unbalance on buses of the substation feed voltage takes place compared to a traditional 25 kV system of traction power supply.