S-Transform Based Pilot Protection Method for HVDC Transmission Lines

Traditional traveling wave protection of HVDC line is easily influenced by fault resistance, and the current differential protection as backup protection has disadvantages of slow operation speed and data synchronization, so this paper proposes a pilot protection method for HVDC line based on S transform. Theoretical analysis shows, for a fault occurring on the forward direction of the protection, the polarities of the fault components of voltage and current detected by protection are opposite, but for a backward direction fault, they are the same. According to these characteristics, a new method based on S transform angle differences to identify the fault direction is presented. In addition, for a pole-earth fault in bipolar HVDC systems, the faulted line can be distinguished from the healthy line in terms of ratio differences of S transform transient voltage energies. Simulation results show that the proposed method can effectively identify internal and external faults, the faulted line and lightning disturbance in different fault conditions.