Research On Aging Mechanism And State Evaluation Of Zinc Oxide Arrester

UHV AC/DC transmission technology and smart grid have achieved rapid development in China,transmission and transformation systems need to prevent damage caused by overvoltage during operation to ensure the safety and reliability of power grid operation.Zinc oxide arrester is the core electrical equipment for power transmission overvoltage prevention in power transmission and transformation projects.It withstands overvoltage surges and working voltages during service,and to a certain extent,there is an aging degradation phenomenon,which directly restricts the efficient operation of power transmission and transformation systems.Based on this,this paper puts forward the subject of"Research on aging mechanism and state evaluation of zinc oxide arresters."This paper relies on high voltage and insulation theory and conducts electric field simulation studies of zinc oxide surge arresters to explore the voltage gradient and electric field distribution of zinc oxide arresters under service conditions.Constructing an aging test platform to conduct heat aging,corona aging and impact aging tests to investigate the association rules of the breakdown characteristics and pressure-sensitive characteristics of different aging levels of zinc oxide varistors,and the change regulation of the breakdown characteristics of different aging levels of silicone rubber,and then revealing the aging mechanism of zinc oxide varistors and silicone rubber.To carry out the polarization and depolarizingcurrenttestofthevaristor,thenexploringtherelationshipof polarization/depolarization charge differences of varistors with nonlinear coefficients and aging degree.This aims to propose a non-destructive evaluation method for the service health status of zinc oxide surge arresters based on the dielectric properties in the time domain.Depending on theoretical research and experimental data analysis,the following mechanisms and laws are obtained:?1?The overall voltage distribution of zinc oxide surge arresters is evenly distributed,and the potentials are similar in the longitudinal direction.The center potential of the parachute skirt is the highest and the lateral direction is decreasing outward from the center.There is a difference in the electric potential between the outer sheath parachute skirts at various levels.And the longitudinal difference between the small and big outer sheath parachute skirts is largest,and then the electric potential difference of the middle-small outer sheath parachute skirts is larger.At last the electric potential difference of big-middle outer sheath parachute skirts is smaller.?2?With increase of surge voltage level and times of impacts,the variation rates of varistor voltage,breakdown voltage and nonlinear coefficient of varistors under lightning impact are the greatest.The affect of DC aging is the second and AC aging affects minimal.?3?The breakdown voltage decreases overall with the increase of aging degree of Corona aging and thermal aging.Among which lightning impact corona is the strongest,AC corona is the second,and DC corona is the smallest.Based on the comparison test results,obtaining that nano based modification can enhance the properties of silicone rubber prominently,such as high temperature resistance,corona resistance and anti-aging.?4?When the aging degree increases,the polarization/depolarization current curve of the varistor rises significantly.Impacting can cause the drastic changes of schottky barriers.Establishing the function correlation between the macroscopic electrical parameters of the varistor and the microscopic characteristic quantities based on?_eff?28?A₁*ln?7?A₂*?7?i_pol-i_dep?8?.?5?Based on the variation law of the polarization/depolarization charge difference and the nonlinear coefficient and aging degree,establishing the function relationship between polarization depolarization charge difference and the average service life of varistor based on Q_PDC?7?Y?8??28?E₁*ln?7?E₂?10?E₃*Y²-E₄*Y³?10?E₅?8?.Therefore,we can evaluate the service health status of zinc oxide lightning arrester non-destructively based on the polarization/depolarization charge difference.Relied on the comprehensive study of theory and experiment in this paper,the evaluation function of the average service life of zinc oxide varistors based on polarization and depolarization charge difference is explored,which can provide theoretical support and practical guidance for the non-destructive evaluation of service status of zinc oxide arresters.