Abstract: Taking a main transformer trip event in a substation as the entry point, this paper analyzes the process in which wiring errors in the voltage transformer secondary circuit cause zero-sequence voltage distortion and further lead to maloperation of multiple main transformer protections, covering electrical principle, protection logic, monitoring system, and operation procedure. The analysis reveals technical deficiencies in the current operation system, including separate monitoring of internally generated and externally introduced zero-sequence voltage, lack of anti-misoperation locking for key procedures, and low integration of state information. Therefore, a countermeasure system covering four links, namely pre-operation risk prevention, real-time verification during operation, active detection before energization, and intelligent monitoring during operation, is constructed to improve the intrinsic safety level of secondary circuit operation and the system state perception capability.