MOA On-line Monitoring And Expert Diagnosis System

As the overvoltage protection device of power system, metal oxide surge arresters (MOA)safe operation has a very important significance to the entire power system.MOA becomes aged and damp due to overvoltage, serious surface contamination, internal moisture and other factors. In this process, little change happens in the total leakage current, but the resistive current which is about10%-20%of total leakage current increase greatly. So the resistive current can reflect the deterioration process of MOA. MOA have nonlinear resistance, its resistive current contains fundamental resistive current and high harmonic resistive current (third, fifth harmonics and so on). System voltage harmonics have less impact on the fundamental resistive current than on the high harmonic resistive current. So this paper makes the fundamental resistive current as the judgment of the MOA performance.Based on the research of the MOA on-line monitoring and combined with the actual project, this paper adopts harmonic analysis method to design the MOA on-line monitoring and expert diagnosis system. The on-line monitoring system combines PIC18F4520and ATT7022C as the hardware architecture. It uses IEC60870-5-103protocol to upload the data to the computer through the RS-485bus or through the GPRS. Based on the real-time monitoring data, the historical data and the environmental parameters, the expert diagnosis system in the computer can analyze and judge the MOA operational status. The system has taken many anti-jamming measures to make the measurements more accurate. The system is put into operation in Huangshan Xintan Substation in December2012. It shows that the35KVMOA total leakage current is about200μA and the resistive current is about20μA. The result is consistent with the theoretical value of the35KVMOA. The system is running well and the measurement data is stable.