Research for the fast distance protection of transmission lines based on equal transfer processes

Taking into account the error caused by differential, two factors´ impact on the distance protection algorithm after equal transfer processes are studied, including the sampling rate and cut-off frequency of the low-pass filter. It comes to a conclusion that increasing the sampling rate can reduce the error caused by differential and cutting down the cut-off frequency can reduce the variance of the least square method, which is verified by the ATP simulation and dynamic physical simulation results. Combined with the simulation results, the impact caused by the length of data window is studied by analyzing the performances of the proposed algorithm. By optimizing the sampling rate, the cutoff frequency, and the length of data window, the distance measuring error can be achieved within 5% at approximately 10ms after the fault occurrence.