Properties of novel traction polyphase rectifier transformer

Dc tram traction voltage is obtained by rectifying grid ac voltage with help of transformer-rectifier sets. In Poland typically 6- or 12-pulse systems are used. 24-pulse system may be achieved by parallel operation of two Yyd transformers with primary windings arranged as zigzag. This paper deals with 24-pulse system design using cost-effective transformer with partially integrated secondary windings. Generation of secondary side voltages is explained. We prove that in spite of secondary phase voltages being of correct magnitude and shift angle, this transformer will never operate with more than 12 pulses. Results of computer simulations are verified by lab tests results.