A study of open-line fault in transformer of a six-phase diode rectifier system with tap-changer

A typical broken line fault sometimes occurs in a six-phase diode rectifier system with diode tap-changer. A detailed theoretical analysis of this phenomenon is presented in this paper. Simulation and experiments have been carried out to verify the validity of the theoretical results. It is pointed out that the six-phase converter with one broken line is equivalent to parallel connection of two single phase rectifiers. The output DC voltage takes the waveform of a positive semi-sine, which causes severe DC ripple and electromagnetic interference (EMI). Most of the load current flows through the bridge connected with the star winding, whereas a small amount through the bridge connected with the delta winding. The conclusions are very significant to choose parameters of the transformer and rectifier diodes. Furthermore, it is important to the fault diagnosis and the real-time processing.