Study On Surface Discharge And Failure Models Of High Harmonic Voltages On Oil-paper Insulation Of Converter Transformer

The voltage waveform of oil-paper insulation structure in the converter transformer includes AC voltage,DC voltage component and a large number of harmonic voltage components.The electric field distribution of its oil paper insulation is significantly different from that of ordinary power transformers.In this paper,the characteristics of surface discharge,short-time voltage tolerance and multivariable failure model under the condition of harmonic component in the oil paper insulation of converter transformer winding are studied.The main contents of the paper are as follows:(1)Surface discharge characteristics of oil-paper insulation under harmonic voltage are experimental studied.The discharge test data of the oil paper insulation under different harmonic content and phase are obtained.The PDIV,discharge repetition rate and maximum discharge volume of oil-paper insulation are analyzed at the different harmonic contents,frequency and phase.The results show that the harmonic content and phase have a significant impact on the surface discharge characteristics of the oil-paper insulation.The harmonic content has little effect on the initial discharge voltage of the oil-paper,but the harmonic content will seriously affect the maximum discharge and repetition rate of the surface discharge.And the harmonic phase decides the surface discharge position of oil paper insulation.(2)The breakdown data of oil-paper insulation under different test voltage waveforms are obtained,and the analytical results of the theoretical model are in agreement with the experimental results.In addition,the influence of harmonic contents,frequency and phase on breakdown voltage of oil-paper insulation were investigated.The experiment results showed that,the breakdown voltages of oil-paper insulation structure under harmonic voltage decreased with increasing harmonic content.(3)The electrical aging test characteristics of oil paper insulation under harmonic voltage components were carried out.Through experiments,the failure time and breakdown voltage of oil-paper insulation under different voltage waveforms are obtained,and the test data are processed by Weibull distribution function.The results show that the insulation failure data of oil-paper obey Weibull distribution,and the voltage tolerance ability of oil-paper decreases with the increasing of harmonic content.The main reason is that the harmonic component makes the surface discharge more seriously,and the insulation life of oil-paper is greatly shortened.(4)A multivariable Weibull failure model of oil-paper insulation considering harmonic content and electric field strength is established.Multiple regression analysis method is used to calculate the parameters of the failure model,and the function relation between the electric field,harmonic content and the failure time of the oil-paper insulation is obtained.Two hypothesis testing methods are used to test the accuracy of the model,and the results show that the model can effectively predict the electrical aging life of oil-paper insulation.