New type of feeding transformer for AC railway traction system

At Shinkansen substations in Japan that receive electric power from an extra-high voltage system, we have been using modified Woodbridge connected transformers for traction power supply since the inauguration of the Sanyo Shinkansen, which commenced commercial operations in March 1972. However, this transformer is of a rather complicated structure. Therefore, we studied a new type of transformer, equipped with equal functions, however a simpler mechanism as compared with a conventional one. We termed the transformer a roof-delta connected transformer since it has a roof-winding and a delta-winding. The roof-delta connected transformer expectable to decrease costs by reducing quantity of winding. We fabricated roof-delta connected transformers for trial at 66kV-voltage. We performed various tests including measurement of neutral phase current. Test results revealed that this transformer is applicable to the used in AC traction feeding system. The first practical roof-delta connected transformer is going to be installed at a new Shinkansen substation constructed by JRTT. JR East is also planning at present to install them at existing Tohoku and Joetsu Shinkansen substations for their renewal. This paper describes the fundamental characteristics of the roof-delta connected transformer and the test results.