Detection Methods For Insulator Surface Pollution Components And The Influence Of Pollution Components On Ac Flashover Performance Of Insulators

With the rapid industrialization and economic expansion,the components of pollution for outdoor insulation are increasingly complex and diversified.The chemical composition of surface pollution have significant impacts on the electrical performance of insulators,and therefore influences the reliability and stability of power system.However,traditional outdoor insulation design and flashover voltage prediction methods have not fully considered the impacts of diverse pollution components.Based on literature reviews on the research of pollution components in outdoor insulation,theoretical and experimental works were carried out to improve the detection methods for insulator surface pollution components and to study the influence of pollution components on AC flashover performance of insulators.This thesis proposed an ion-pairing model to examine the chemical compounds of insulator surface pollution.The influence mechanism and microcosmic behavior of pollution components on insulator flashover performance were analyzed.Considering the effect of various types of pollution components on insulator flashover performance,a prediction method of insulator flashover voltage gradient were proposed.The detailed work and main contents are as follows:Natural pollution accumulation tests were conducted on several types of insulators with the measurement of equivalent salt deposit density(ESDD)and non-soluble deposit density(NSDD).The contents of anions and cations were obtained by using ion-exchange chromatography.An ion-pairing model based on pollution accumulation and dynamic conductivity properties was proposed.This model can address the deficiencies in manual ion-pairing method.In this model,fuzzy clustering and dynamic improved FCM were adopted to gain the main chemical compounds in natural pollution.The dynamic conductivity properties of general contaminants in outdoor insulation were studied.The relationships among conductivity,dissolution time and equilibrium concentration were also obtained by modifying Avrami solution kinetics equation.Finally,an ion-pairing sub-model based on dynamic conductivity property was built.This sub-model was verified by tests and can be applied to improve the accuracy of ion-pairing.Insulator flashover characteristic parameters of various soluble salts were obtained from flashover tests of insulators by changing single soluble contaminants in each test.General influence rule was summarized as:Cl^-<NO₃^-<SO₄^2-;K⁺<Na⁺,NH₄⁺<Ca²⁺.Insulator flashover parameters prediction formula based on freely soluble constituents was proposed.The engineering application and value of the proposed formula were also analyzed.Flashover tests of insulators polluted by mixed soluble contaminants were also carried out.Results indicate that,linear superposition method can be used to predict the flashover voltage gradient of insulators polluted with freely soluble contaminants.The slightly soluble constituent Ca SO₄ needs to be calculated according to its conductivity property separately.Based on flashover tests of insulators polluted by different non-soluble contaminants,insulator flashover characteristic parameters of various non-soluble components were obtained.The ordering of the impact of contaminants was found as:kaolin<Al₂O₃<Fe₂O₃,kieselguhr<Si O₂.Additionally,the increasing particle size of non-soluble contaminant can result in the increase of insulator flashover voltage.The calculated particle stack structures indicate that,water retention effect of particle gap plays the leading role in the influence of particle size on insulator flashover performance.Based on electrolyte dissolution tests and molecular dynamics simulation,this thesis studied the mechanism of how pollution constituents affecting insulator flashover performance from various aspects including conductivity and dissolution properties,temperature,electric field and mixed ions interaction effect.Results indicate that,conductivity property and solubility of salts should be considered in the process of effective ESDD measurement and calculation.Different soluble constituents correspond to different temperature modification coefficients.The ionic conductivities of solutions increase in different degree when electric field applied.The influence of co-existing ions on solution conductivity mainly performs as solvation effect and ion atmosphere effect,and ion atmosphere effect plays a leading role.The effect of adding ions on the aspects of diffusion coefficient is opposite to its effect on the solubility of Ca SO₄solution.This thesis also studied the water sorption mechanism and microcosmic behavior of non-soluble contaminants,and introduced a microcosmic model of water sorption by using molecular dynamics and Monte Carlo method.The surface sorption,pore sorption and layer sorption effects of non-soluble contaminants were analyzed in the aspects of adsorption energy,radial distribution function,potential of mean force,adsorption isotherm,adsorption dynamics,etc.The results of molecular simulation and flashover tests showed good agreement.According to the dissolution and conductivity properties of pollution components,the effective pollution grades of soluble salts were quantified.Based on the influence mechanisms of pollution constituents on insulator flashover performance and ion-pairing results,the flashover voltage(gradient)prediction method of insulator polluted by mixed contaminants was proposed.This set of prediction method takes the combined action of freely soluble,slightly soluble and non-soluble contaminants into consideration,and can be applied in outdoor insulation engineering.This thesis also conducted experiments to verify the proposed prediction method.Results indicate that,comparing to traditional method,the error of proposed method can be decreased significantly.This error can be controlled within 10%.