Study On The Effect For Relay Protection Based On Non-linear Elements

With the continuous development of industry, non-linear elements have become an important part of the power system. It is a knotty problem that mal-operation of power system relay protection caused by transformer switches and electric arc furnace. Considering a case of mal-operation of differential protection of main transformer with bridge connection, it is further analyzed on the impact of inrush current, sympathetic inrush current and CT saturation. Furthermore, the reasons of the mal-operation transformer of differential protection are analyzed in the dissertation. Finally, a new method which is based on the time differential method and some other measures are proposed to prevent differential protection form mal-operation. Adverse effects of EAF on power system relay protection is mainly mal-operation of starting component which was caused by random EAF current. Taking a case of mal-operation of starting component, this paper presents a novel model of EAF. A new start-up criterion and a novel trouble-free quickly return method and comprehensive treatment of EAF are proposed to prevent differential starting component form mal-operation. Simulation results validate new measures feasibility and reliability.