Fault Analysis and Protection in Flexible DC Traction Power Supply System

Fault analysis and protection are crucial for the development of flexible dc traction power supply system (DC-TPSS) in urban rail transit. The aim of this study was to provide a comprehensive review of fault analysis and protection in flexible DC-TPSSs, in particular the adaptability and development trend of protection. A model of a flexible DC-TPSS was built using bidirectional converter and traction network, and the detailed fault analyses of pole-to-pole fault and pole-to-ground fault were conducted. The correctness of the model and fault analysis is verified by electromagnetic transient simulation. The fault analysis findings suggest that the fault current is extremely high and develops rapidly. In the case of pole-to-pole fault, the peak current for near end short circuit can reach approximately 60 kA within a few hundred microseconds to several milliseconds. Furthermore, through adaptability analyses of existing protection principles, these indicate that the direct acting and current-based protection principles have deficiencies in terms of speed, sensitivity, and reliability. It is necessary to recalculate the settings to meet the new requirements of protection. Finally, the new trends in protection are described to provide references for further research.