Research On Key Technology For Risk Warning Of Contamination Flashover For Cantilever Insulators In Overhead Contact Lines

With the development of construction and operation of electrified high-speed railway,higher reliability of electrified power supply system was required by the criss-cross huge railway network.But contamination flashover of insulators in overhead contact lines has been threatening the reliability and safety of electric traction power supply system till now.Technical management actions against pollution flashover of insulators in overhead contact lines contains of increasing creep distance,painting waterproof material on the surface of insulators,replacing porcelain insulators with polymer insulators in the heavy pollution electrified railways area,and periodical washing or cleaning.These measurements belong to passive actions that bring about partially reducing happening of flashover,and cause the waste of labor cost and material resources.Sometimes pollution-flashover just happens between two periods of washing or cleaning.One case of pollution flashover means thousands of insulators have been in the risk of flashover in the same area.So the ability to forecast the warning of flashover could directly affect reliability of traction power supply,labor cost put into the insulator maintenance on overhead contact line,as well as utilization efficiency of maintenance window of power supply.With the improving of automation level of traction power supply management system,forecasting the level of insulator surface contamination and risk of pollution of flashover has been becoming urgent needs.On-line monitoring system for pre-warning of insulator pollution flashover in overhead contact lines has been one part of electrified railway power supply system inspection and monitor clusters according to China Railway.The dissertation focuses on the demand of inspection and monitoring of power supply system,researches on the key technology of pre-warning of pollution flashover for cantilever insulators in overhead contact lines.Series of QB-25 cantilever insulators in overhead contact lines serve as test samples in the artificial contamination test in the dissertation,leakage current is collected under the condition of different contamination level of the sample insulator.Based on testing data of leakage current under the circumstances of saturation humidity and OCL operating voltage on cantilever insulators,Wavelet Packets and Empirical Mode Decomposition method,Power Spectrum Calculation with the Welch method,Harmonic Current Analysis are applied to analyze the leakage current characteristic of time domain and frequency domain.Considering the result of analyzing of leakage current characteristics,the leakage current effective value,the standard deviation of effective value,the mean effective value,the effective maximum value of third harmonic and the third harmonic content are selected as input variables to initiatively construct the pollution Flashover Index for the cantilever insulators.With an important application value,the flashover index model could be applied in contamination on-line monitoring system practically as scientific basis for diagnosis and evaluation of contamination level of insulator.The research contents and main creative points in this dissertation are concluded as following:With series of QB-25 cantilever insulators in overhead contact lines serving as test samples for the first time,artificial contamination test is designed and carried out to collect the leakage current on the condition of four levels of contamination ESDD values of 0.05 mg/cm2,0.15 mg/cm2,0.25 mg/cm2,0.35 mg/cm2.The test fills in the gaps of artificial contamination test of OCL cantilever insulators for high-speed railway.Algrithm of time-frequency analysis method based on Wavelet Packet plus Empirical Mode Decomposition is put forward initiatively in the dissertation to calculate the leakage current time-frequency spectrum of cantilever insulators in OCL.Disadvantage and advantage for the four kinds of wavelet threshold are compared concerning the denoise effect,and then adaptive threshold method is used for leakage current testing data processing.Based on typical method of time-frequency analysis,the superiority of Algrithm of time-frequency analysis method of Wavelet Packet plus Empirical Mode Decomposition is verified as far as reproducing the original local time-frequency characteristics of leakage current signal is concerned,while Wigner-Ville method produces cross-term interference and makes leakage current signal's original features fuzzy.The pollution Flashover Index for the OCL cantilever insulators is created initiatively in the dissertation which could be applied into contamination on-line monitoring system based on leakage current measuring and to evaluate the risk of pollution flashover with output of the flashover index and contamination degree estimation.When the surface contamination degree is varying,different leakage current characteristic variables would be affected in different degree.In order to eliminate invalid and redundant features,choose the ideal inputs to construct and calculate the flashover index,the dissertation dose detailed research in many leakage current characteristics to figure out which are significantly suitable for reflecting the polluted degree changing and describe flashover information more adequately.After the analyzing of leakage current properties in time domain and frequency domain,the leakage current effective value,the standard deviation of effective value,the mean effective value,the effective maximum value of third harmonic and the third harmonic content are selected as input variables to initiatively construct the pollution Flashover Index for the cantilever insulators.Sigmoid Function is adopted for normalization processing of the five invariables.The effectiveness of the Flashover Index model for cantilever insulators is verified by experiments.FOI index could serve power supply management department as the scientific basis for evaluating insulation status and making insulators maintenance plan.To put into application,FOI index would play an important role in prompting the transform of insulator maintenance method from plan-oriented to status-oriented.