| China has a large-scale railway network,High-speed railways have been opened to traffic in areas with high-cold environments and the government has planned several main high-speed railways.The traction power supply system,as we all know,plays an important part in the operation of high speed train,it is the only power supply of high-speed railway.the highvoltage bushing is the only channel where links the internal unit of transformer and the external power network,and also is the weak part in the system.Aiming at the problem that the damage rate of high-voltage bushing of high-speed railway in alpine area is much higher than that in other areas,In view of the problem that the damage rate of high-speed railway high-voltage bushings in the high-cold area is much higher than that of other high-speed railways,if the risks caused by equipment insulation defects cannot be detected and eliminated in time,huge production accidents may be caused.While moisture of insulation is the most typical insulation defect of high-voltage bushings.It is particularly important to study the electrical characteristics of oil-paper insulation of bushings and the nondestructive evaluation method of insulation state to ensure the stable operation of traction power supply system at low temperature.In view of the problem that the breakdown characteristics and voltage distribution characteristics of bushing oil-paper insulation with different moisture content in low temperature environment have not yet been explored.In this paper,the breakdown test platform in low temperature environment is designed and built,and the multi-layer bushing oil-paper insulation with different moisture content are prepared.The breakdown characteristics are tested at different low temperatures,and the breakdown voltage distribution at different temperature and moisture content is obtained.The effects of moisture and temperature on the breakdown characteristics are studied,and the micro morphology and mechanism of the breakdown channel are analyzed.In order to further study of the frequency domain dielectric spectroscopy characteristics suitable for the dampness of the typical bushing multilayer oil-paper insulation in low temperature environments,a low temperature dielectric response test platform is built,and the dielectric response tests of casing oil paper insulation samples with different low temperature and moisture content are carried out.The complex capacitance spectra under different low temperature and moisture content are obtained,and the effects of moisture and temperature on complex capacitance are studied.In order to fully excavate the data characteristics of the frequency domain dielectric spectroscopy obtained by the test,the dielectric spectroscopy is analyzed by gray wolf optimization algorithm,parameter constraints and Dissado-Hill(D-H)model.The dielectric parameters in the D-H model of samples with different moisture content under different test temperatures are obtained,and the influence of moisture and temperature on the dielectric parameters is analyzed.The D-H dielectric parameters with strong correlation with the changes of moisture and temperature are extracted,and the three-dimensional numerical relationship between the parameters and moisture content and temperature is established.A method for evaluating the moisture content of oil-paper insulation of bushing in low temperature environment is proposed and verified,which can provide relevant guidance for the operation and maintenance of bushing and the nondestructive evaluation technology of oilpaper insulation of bushing in low temperature environment. |
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