Research On On-line Monitoring Technology For The Resistive Leakage Current Of Zinc-Oxide Surge Arrester

Since the 70's of the twentieth Century,Zinc-Oxide surge arrester has gradually replaced the traditional Silicon carbide arrester and become the main protection equipment which is able to limit the over-voltage,reduce the insulation level and improve the operation reliability in power grid.It is Zinc-Oxide surge arrester that has many unique advantages,such as no-gaps,huge flow capacity and good nonlinear characteristic.However,the gradual deterioration of the resistance valve block and the sealing element is associated with the increase of the leakage current and even the thermal breakdown or explosion of Zinc-Oxide surge arrester.Therefore,in order to ensure the safe and stable operation of power system,it is particularly important to on-line monitor the operation condition of Zinc-Oxide surge arrester by a reasonable method in the running process.According to the advantages of different resistive leakage current extracting methods and the conclusions of leakage current harmonic analysis at zero-crossing of voltage,a new extracting method is proposed in this paper.The mathematical derivation proves that this new method can not only eliminate the interference of the harmonic voltage and the inter-phase coupling capacitance completely,but also avoid the influence which comes up with the fault of one phase arrester,the differences of three phases and the fluctuation of voltage.Therefore the operation and status of Zinc-Oxide surge arresters will be diagnosed timely and precisely,based on extracting the resistive leakage current accurately through the new method in this paper.Because of the low leakage current which value is only milliamperes level,the accurate measurement of the Zinc-Oxide surge arrester leakage current is an important part of the on-line monitoring technology.In order to meet the requirement of engineering,this paper realizes the non-contact measurement of milliamperes current by the current sensor with Microcrystalline alloy core and Rogowski coil.The traditional on-line monitoring methods are generally required to extract the running operation voltage signal of the Zinc-Oxide surge arrester from the voltage transformer of power system.However,those methods are so complex that their economic and security performances are not well.According to the need of new extraction method and the special structure of three-phases,the B-phase voltage zero-crossing detection device is designed in this thesis.Not only the structure and principle of the device is simple,and the economical performance is well,but also the operation security of the on-line monitoring technology is guaranteed with the non-contact detection.