一种±500 kV混合双极高压直流输电线路保护的新方法

Aiming at the problems of long distance and high failure rate of hybrid bipolar high voltage direct current (HVDC) transmission lines, a relay protection method suitable for ±500 kV hybrid DC transmission lines is proposed. According to the different high and low frequency energy of the signals on the two sides of the boundary element of the hybrid bipolar HVDC transmission line, and considering the type of fault and the influence of the transition resistance on the result, a protection scheme for the transient energy ratio of the active power fault component is constructed. This method adopts wavelet packet transform to decompose the active power fault component to obtain the transient energy of each node. The positive and negative energy ratios are used to distinguish between internal and external faults, the differences between positive and negative energy ratios are taken to distinguish single faults from bipolar ones, and the positive and negative part of the frequency band energy sum is applied to fault selection. The electromagnetic simulation software PSCAD/EMTDC is chosen to constructed a ±500 kV hybrid bipolar HVDC transmission system simulation model, and MATLAB is used to combine the protection criteria to perform the simulation verification of the protection algorithm. This proposed method is endowed with high resistance to transient resistance and a data acquisition time window of 3 ms, which enables to quickly and accurately identify internal and external faults under different operating conditions with a fault pole selection function.