An accident analysis of a smart substation

This article records and analyses an accident happened in a 500kV smart substation, which was caused by a single-phase ground fault happened to a 500kV transmission line in the power grid. The accident provoked false action of the differential protection of main transformer, false action of the differential protection of 220kV bus and false action of line differential protection of several 220kV transmission lines. The accident caused the power losing of transformer, several 220kV transmission lines and 220kV north bus. Through the analysis of the fault wave of the tripping devices, we know that these false actions of differential protections were caused by the un- synchronism of sampled data of current of 220kV equipments supplied by merging units. This accident show the importance of the synchronism of sample data, so it´s an essential step to examine synchronism of the MUs in the smart substation before it puts into operation.