Simulation of secondary equipment lightning protection in EHV substation based on ATP

Two lightning accidents occurred in a 500 kV substation are analyzed: the lighting intrusion on the se-condary circuit of telecontrol system causing line and the lighting interference in the proper operation of monitoring system.Analysis pointed out that the equipotential earthing mode of substation secondary system is wrong,which causes the potential difference between two ends of secondary equipment and damages the equipment.The three earthing modes of substation secondary equipment are discussed:floating-point,one-point and multipoint.Series one-point and parallel one-point earthing are analyzed.The latter is widely used in substations.The simulation model of parallel one-point earthing is built with ATP graphic pretreatment program and the lighting current leaked into substation earthing grids via arrester is simulated with Slope-Ramp.Results show that,the application of mixed earthing system in secondary equipment for high and low frequency signals and the equipotential connection among secondary equipments are the key measures to prevent accidents.