Abstract:Whether the current, voltage, switching amount and other external binary input values collected by relay protection device of power system in real time are correct or not directly affects the correctness of relay protection action. Based on engineering practice, this paper analyzes the phenomenon that the 220kV main transformer protection device in a substation has abnormal acquisition opening during commissioning process. First, the fault opening loop of the main transformer protection in the event is tested. It is found that the reason for the anomaly is that the leakage current of the stabilized tube is too large, and the anomaly of the stabilized tube is analyzed from the three modes of failure of the stabilized tube. Secondly, the voltage and current of the key points of the fault and normal open loop are compared by means of test and simulation, and the reasons for the failure of the opening and entering of the protection device are further clarified. Finally, two kinds of solutions are proposed. and ultimately from the perspective of economy and security, an optimal solution is selected. The plug-in with an on-field transistor with a pull resistance of 1kΩ is replaced by a resistor stabilizer. which avoids the huge risk of the power grid caused by the protection refusal and maloperation.