Extremely low frequency-based faulty line selection of low-resistance grounding system

The single-phase-to-ground faulty line selection methods based on the signals of the frequency above 10 Hz has a low discrimination of fault characteristic signal and characteristic signal may be covered by noise in cases of high-resistance fault. To solve the problem, a line selection method based on system's own extremely low frequency signal (SOELFS) is proposed. Due to the obvious attenuation characteristic of extremely low frequency signals in healthy lines, the extremely low frequency signal has a larger discrimination and hardly affected by imbalanced current noise. Moreover, as the amplitude of the SOELFS is affected by the initial phase angle of the fault, an additional line selection method based on artificially injected extremely low frequency signal is proposed. Cooperating with the specially designed and implemented measuring device, simulations and experimental verification are carried out. The results show that the discrimination of characteristic signal increases from 31 obtained by power frequency to more than 500, the high-resistance fault protection ability increases from 2 to 10 k omega.