Pollution Discharge Characteristics And Structure Optimization Of Composite Arrester Combined Insulator

The operation cases at home and abroad in recent ten years show that the flashover accidents caused by unreasonable insulation configuration and serious pollution have not been eliminated,and seriously endanger the safety of power system.In order to prevent lightning from damaging transmission line equipment and safe operation,lightning protection equipment such as parallel gap and zinc oxide arrester are widely used,but they are usually used together with insulators to form a combined insulator.Therefore,there are some problems,such as whether the insulation coordination is reasonable and how to configure the external insulation under the condition of pollution of combined insulators.At present,although the research on the arc development process and flashover model of polluted insulators is more in-depth,the research on the discharge characteristics of combined insulators under polluted conditions is relatively lacking.Therefore,taking a composite arrester combined insulator as an example,this paper focuses on the arc development mechanism and flashover model,reveals the pollution flashover characteristics of combined insulator through experiments,and analyzes the law of arc development path under pollution conditions.The research results are helpful for a deeper understanding of the formation and discharge development mechanism of pollution flashover of combined insulators,and can provide a more scientific and comprehensive theoretical guidance for the design of transmission line combined insulators under pollution conditions.The main research work and achievements of this paper include:The arc development path of combined insulator is analyzed theoretically,and the arc development mechanism is revealed;In order to solve the inapplicability of traditional insulator flashover model to combined insulator,the physical model of AC arc critical development of combined insulator is proposed,and the dynamic AC combined insulator flashover model is deduced and established.(1)According to the equivalent circuit of composite arrester combined insulator,the arc path under AC voltage is analyzed.Combined with surface insulation,air gap and volt second characteristic curve of arrester,the arc path under impulse voltage is analyzed.(2)Based on the types of arc paths analyzed,and based on Obenaus model and Hampton criterion,the critical physical models for the development of four types of arc paths under AC voltage are proposed;Combined with the critical physical model of arc development,considering the complex geometry of combined insulator and the nonlinear resistance characteristics of zinc oxide valve plate of arrester,the calculation formula of residual pollution layer resistance suitable for combined insulator is deduced;The flashover model of dynamic AC combined insulator is established.(3)The calculation method of impulse flashover voltage and arc path of composite arrester combined insulator based on intersection method is proposed.Starting from the iterative solution of variable U,the problem of single equation and two unknowns is transformed into the problem of solving single unknown nonlinear equation to realize the solution of the model.Relying on the platform of the State Key Laboratory and the national field scientific observation and research station,(1)firstly,the key parameters of the flashover model of composite arrester combined insulator proposed in Chapter 2 are tested,and the key data such as the calculation formula of surface pollution layer conductivity and the calculation formula of single insulation volt second characteristic curve suitable for combined insulator are obtained.(2)The discharge tests of combined insulators under AC and impulse voltage are carried out.Through the comparative analysis between the model calculation results and the test results,it is found that the maximum error of dynamic AC flashover model is 10.3% and the average error is 6.3%;The maximum error of impact flashover model based on intersection method is 8.1%,and the average error is 4.5%.(3)Based on the test results,the variation laws of AC,lightning impulse and operation impulse flashover voltage of combined insulators under polluted conditions are revealed.In addition,taking lightning impulse voltage as an example,the flashover probability of combined insulator under different pollution degree is calculated based on Weibull distribution.The test studies and reveals the development law of arc path of combined insulator during pollution.(1)under AC voltage,the arc path is only affected by the pollution degree,and its discharge path can also be divided into three cases,namely T1(arc path is air gap),T2(air gap protection fails but the arrester works normally)and T3(air gap protection fails and the arrester has external insulation flashover).(2)However,under impulse voltage,the arc path is affected by both pollution degree and impulse voltage amplitude.In addition to the influence of ESDD,the development of arc path is related to the applied impulse voltage waveform.(3)The characteristic parameters of impulse voltage waveform under typical arc path are proposed and defined,and the correlation between impulse voltage waveform parameters and arc path is analyzed based on grey theory.Finally,the flashover model is verified.The predicted results of AC and lightning impulse discharge paths are in good agreement with the experimental results,which are 90.9% and 100% respectively.The structural optimization principle and index analysis of composite arrester combined insulator are carried out,and an optimization method based on the combination of combined insulator flashover model and genetic optimization algorithm is proposed.In this paper,the flashover voltage and arc path calculated by the flashover model of combined insulator are proposed as the optimized boundary conditions.Therefore,on the premise of ensuring that the arc path develops along the ideal position,higher withstand flashover voltage(smaller and more uniform surface electric field characteristics)can be obtained.Through the optimization calculation by genetic algorithm,the recommended structural parameters of composite arrester combined insulator under different pollution levels are finally obtained.Taking the class c pollution area as an example,the final optimization parameters are: the diameter of arc guide foot,the distance of protective gap and the extension length of umbrella are27.6mm,29.7mm and 42.4mm respectively.