Study On Leakage Current Characteristics Of Insulators For Over-head Contact System Based On Monitoring Data Of Leakage Current

Cantilever insulators for over-head contact system is a specific type insulators of electrified railways, which mostly composed by cantilever ceramic insulators in China. The pollution rules of cantilever insulators are complex and the pollution flashover takes place frequently. Each pollution flashover will not only cause loss of power in traction substation, even traction power supply system oscillation, but also black-out in large area and transmission line outage, which seriously affect the operation security of electrified railway. So reaching of measures against pollution flashover occurring in Cantilever insulators for over-head contact system has great significance.The shortcoming that the currently exiting characteristic parameters of leakage current could not precisely reflect the operating conditions of insulating surfaces, flashover and mechanism of surface discharge was analyzed. According to the corresponding characteristics between the phenomena in the overall process of contamination discharge and the waveform of leakage current, the leakage current was separated into stray-pulse, pulse-sequence sinusoidal and triangular components per half-wave of power frequency. Characteristics of composition of leakage current components were analyzed, the basic composition unit of leakage current, the leakage current half-wave, is presented. Characteristics of waveform of leakage current’s four components in time domain and frequency domain is studied, three waveform parameters of half-wave which containing the time lag to onset, the ratio of accumulated charges and distortion level could represent the characteristics of the leakage current half-wave effectively. An extraction method containing three key thresholds based on the remarkable difference of three waveform parameters of four components’ half-wave was presented. The complete flow chart of the extraction method of four components and the programming of the extraction method in Matlab were presented. Then, man-made pollution tests of a particular cantilever ceramic insulator were conducted in a laboratory, during which the probability distribution of three waveform parameters for half-wave of leakage current four components were presented. Three thresholds were determined by using OTUS method and bimodal method. The validity of this extraction method was verified by six segments of test leakage current which extracted random. According to leakage current produced on the contaminated cantilever insulator which flashover had happened and the changing characteristics of the cumulative charges of four components in the process of flashover, the operating condition assessment of contaminated insulator based on components of leakage current was determined. The feasibility of contamination prediction based on four components of leakage current was analyzed, through analyzing the difference in cumulative charges and variation trend of four components of two contamination degrees in same operating condition. And the analysis results show that the contamination prediction method based on four components of leakage current could provide a new method for contamination prediction...