Moisture And Aging Level Evaluation Of MOA Based On Electrical And Dielectric Properties

Metal oxide arresters(MOA)are "switches" with certain electrical characteristics.When subjected to overvoltage,"switches" are closed,venting charges accumulated on equipment and lines,reducing voltage amplitude,and avoiding overvoltages to damage electrical equipment and thus ensuring the safe operation of electrical equipment and grid systems.Due to the long-term exposure to the working current and the infiltration of the surrounding environment,the arrester will be aged and damped,and in severe cases,the arrester will explode,which will seriously endanger the safety of the protected equipment.Therefore,research to evaluate the degree of aging and moisture of MOA is necessary for the operational safety of the entire power grid.The arrester has excellent nonlinear characteristics.However,the function describing the nonlinear characteristic is mainly a single exponential function.The applicable current range is narrow and the evaluation is not accurate.On the other hand,the arrester valve as a dielectric ceramic whose moisture and aging state can be reflected by the change of its dielectric properties.Frequency domain dielectric response method(FDS)has been widely used in measuring dielectric properties due to its strong anti-interference ability,but the current FDS-based assessment of MOA only stays in the analysing of the qualitative change of the FDS curve before and after aged,without quantitative analysis,which brings difficulties to the evaluation of MOA.In view of the shortcomings of the above research methods,this paper takes the ZnO valve and the whole MOA as the research object,and studies the correlation between the moisture,aging state and the nonlinear volt-ampere characteristic curve and FDS curve from the two aspects of electrical characteristics and dielectric properties.The following work was carried out:(1)The equivalent model of the arrester valve based on the extended Debye model is established.The equivalent model is solved by the fusion method of genetic algorithm and Levenberg-Marquardt algorithm.All the resistors and capacitance parameter in the arrester model based on the extended Debye model are obtained;the fitting function of the volt-ampere characteristic curve is studied,which has a large degree of coincidence on the order of four currents(2)The ZnO valve accelerated aging platform was built.The FDS test and DC volt-ampere characteristic test were carried out on the arrester valve with different aging degree and under different measurement temperature.The influence of aging level and temperature applied to the FDS,the model parameters of the arrester and the nonlinear characteristics are discussed.(3)The damp test of the arrester valve and the whole arrester were carried out.The FDS test and DC volt-ampere characteristic test were carried out on the arrester samples under different moisture levels.The influence of the degree of moisture on the FDS curve,model parameters and nonlinear curve characteristics of the arrester was discussed.(4)Based on the measured FDS data and DC volt-ampere characteristic curve,the parameters of extended Debye model were identified by GA-LMA algorithm and the parameters of DC volt-ampere characteristic fitting function were carried out.The influence of different temperature,different moisture and different aging degree on each parameter was analyzed.The characteristic quantities of moisture and aging level of the arrester valve and the MOA are excavated from the two aspects of electrical characteristics and dielectric properties.