Developments in d.c. traction power supply rectifiers

Rectifier theory and its application to diode-type power convertors to provide DC power supplies for urban electrified railway systems has long been established and used successfully throughout the world. Traditionally, limitations in diode power ratings lead to large numbers of diodes being required in the rectifier which resulted in the fused design being the industry standard. The development of power semiconductor technology over the last thirty five years has lead to a gradual optimisation of rectifier design with respect to the number of power diodes required to achieve a given power rating. This optimisation has lead to fuseless rectifier design to be both a practical and economic option compared to the traditional fused design. Some transport authorities now readily accept the use of fuseless rectifiers in their traction substations however there is still a reluctance amongst others to consider the use of the fuseless design due to the perceived implications on system operation, reliability and maintainability. This paper describes the evolvement of the traction power convertor with the development of power semiconductor technology, discusses the advantages and disadvantages of the fuseless design and looks at possible future developments.