Characteristics of Cross-Line Fault between Flexible DC and AC Lines and its Influence on DC Traveling Wave Protection

With the development of flexible DC transmission and the shortage of transmission corridors, flexible DC transmission lines may be erected on the same tower or span vertically with traditional AC lines, greatly increasing the possibility of cross-line fault between flexible DC lines and AC lines. This paper focuses on this issue. Based on the equivalent circuit, the short-circuit current at the initial stage of this cross-line fault is analyzed first. Then, based typical ±500kV flexible DC system and Extremely High Voltage (EHV) AC system in China, the simulation model is established in Power Systems Computer Aided Design (PSCAD). The fault transient characteristics of cross-line fault is analyzed, and the significant interaction effect of AC and DC systems is verified. On this basis, the response of DC traveling wave protection to this cross-line fault is tested. Simulation results show that the values and gradients of fault traveling wave decrease under cross-line fault, and the reliability of traveling wave protection decreases.