Research On On-line Monitoring Technology Of Metal Oxide Arrester

Metal oxide arrester (MOA) is one of the main over-voltage protectiondevices in power system. The thermal damage, transient and syntonic over-voltage, inner moistened of MOA and so on, will lead to MOA’s damage evenexploding. To protect the security of power system, it is necessary to monitorMOA on-line, so we can find out the hidden trouble and the anomalies of MOAin time.The measuring of the resistive current of MOA is the main method ofmonitoring the conditions of MOA. At present, the harmonic voltage and inter-phase coupling capacitance are the main interference in extracting the resistivecurrent of MOA. To solve the problem, a new extracting method based on therelationship between total current and its component parts, resistive current andcapacitive current, for resistive current of MOA at A, B, C three-phase voltagezero-point is proposed. The formulas of the new method under normal and thethird harmonic voltage conditions are deduced，and the simulation models underthe two conditions are established to check the accuracy of the method.Comparing the existing methods of extracting the leakage current of MOA,a current transformer with single turn cored structure is designed for the on-linemonitoring system. According to the new extracting method, the hardware circuitand software flow of MOA’s on-line monitoring system are designed. At last, theerror formulas of the resistive current are deduced when the equivalentcapacitance of three-phase MOA are different, and the effect of resistive current’sextracting is checked through the simulation with10kV MOA.The theoretical analysis and simulation testify that the new method caneliminate not only the interference of the inter-phase coupling capacitance butalso the third harmonic voltage, extracting the resistive current of MOA accurately and effectively. Through this method, we can judge the performanceof MOA more reliably.