Zero sequence DC selective characteristic of B3 II-1A leak-hunting relay

With the principle of zero sequence DC selective leakage protection, the selectivity of B3 II-1A leak-hunting relay made in USSR is studied. According to the conducting characteristic of rectifying tubes in its detection circuit, mathematical models of instantaneous detection current circuit and instantaneous leakage current circuit are established for the three periods of a power cycle. The measured current is analyzed by the vector technique, its theoretic value is calculated by the harmonic analysis method and its theoretic waveform is simulated by Matlab. The simulative experiment of power net verifies the consistency of experimental data with theoretic data, which validates the line selection function of B3 II-1A leak-hunting relay.