Research on a New Extinction Coil Operation Mode for Resonant Earthed Neutral System

A great deal of simulation results show that sometimes there is an excessive remnant current even under fully compensated condition when a bolted single-phase-to-ground fault or a single-phase-to-ground fault with low transition resistance occurs in medium-voltage resonant earthed neutral system. In the distribution networks with low damp, the excessive remnant current will occasionally fade down slowly in several hundred microseconds. If this situation happens, the electric arc will hardly be extinguished and the malfunction may be so serious that it will bring more hazard to the distribution network. Based on the above phenomenon, the transient currents of a bolted single-phase-to-ground fault or a single-phase-to-ground fault with low transition resistance under fully compensated condition has been theoretically analyzed in the view of fundamental component. And the fault transient state equations for calculating the coherent electric parameters of a single-phase-to-ground fault have also been deduced. Their curves have been drawn by the MATLAB software and been compared with the fault transient state curves of ATP simulation. The comparison results show that the curves drawn by MATLAB software based on the equations are similar to those drawn by ATP software based on the digital model in a single-phase-to-ground fault. In order to restrain the excessive remnant fault current, a new extinction coil operation mode has been presented in this paper by in-depth analyses and a great deal of simulations.