Earth Fault Detection Method for TN-C-S Systems Based on Residual Current Shunt Coefficients

TN-C-S systems are widely used in low-voltage distribution networks (LVDNs). However, the PEN conductor of the TN-C-S system is earthed at multiple points, causing changes in residual currents during load switching. Existing earth fault detection methods cannot distinguish this residual current change caused by load switching, which will lead to mal-operation. To address this problem, the residual currents during a steady state, load switching, and an earth fault are derived. It is found that the residual current shunt coefficient during load switching is the same as that in the steady state, but is different from that during the earth fault. Record the residual current shunt coefficient when devices are powered on. Then, calculate the residual current deviation shunt coefficient when the residual current changes. Earth faults can be discriminated by comparing the difference between the calculated shunt coefficients and the recorded shunt coefficients. The reliability of the proposed method was verified by both digital simulations and physical tests in an actual LVDN.