Analysis of differential protection action of main transformer with synonymous phase grounding fault in 35kV small current system

Abstract: at 03:19:34 on a certain day, the differential protection of No. 1 Main Transformer in a 35KV substation acted, and the backup protection and 35kV line a protection in No. 2 main transformer in the upper 110kV substation of the station were started but not exported. On site inspection showed that the c-phase porcelain insulator of 3101 disconnector in 35kV section of station B broke and fell, the circuit breakers 302, 310 and 011 of No. 1 Main Transformer tripped accidentally, and No. 1 Main Transformer lost voltage.