Zinc Oxide Arrester Leakage Current Network Monitoring System

The ZnO surge arresters are important over-voltage protection devices. They are widely used in electric power system due to their excellent nonlinear and high surge absorbing capability. Considering that the ZnO surge arresters have canceled gaps, they will deteriorate gradually under operating voltage. Some of them will be moistened because of structure problems. All these can lead to increasing of leakage current of. the arresters. The limitations are inevitable in conventional yearly preventive test of ZnO surge arresters. So it is in need increasingly to research the on-line monitoring technique for the arresters.In this paper, the on-line monitoring technique of leakage current, especially of the resistive leakage current through the ZnO surge arresters under operating voltage is discussed.The existing different monitoring methods are investigated at fist. A new measuring method named resistive basic harmonic current measuring method is introduced. By applying this method, the influence of harmonics in the system voltage on the measuring result may be minimized. So the measuring result may be more reliable. Something is done to improve this method, including selection of reference signal and application of the synthetic relative measuring method. At the same time, this new method can not only isolate system and the instrument electrically, but also transmit the current signal linearly. In respect of data processing, the 89c52 microprocessor is used so that the data may be calculated more accurately. Compared with other methods, it is better used in the electrical station as it has some other feature such as simple structure,high anti-interference ability and reliable performance.With the development of the network technology and the MIS of electric power, test data can be transmitted to the server far away through MODEM. It is convenient and realizable. A practical on-line monitoring system has been developed and operated in the 500 kV Yuntian power station, Hunan Province. Test results show that the monitoring system is effective. We are sure that this on-line monitoring system will play a great role in the condition based maintenance.