Measurement Of Charge Mobility Of Oil Paper Insulation And Calculation Of Space Electric Field

HVDC plays an important role in Chinas "west to East power transmission" and other high-power and long-distance transmission projects.Converter transformer is the core equipment of HVDC,which plays a key role in AC-DC conversion.The statistical results show that the converter fault is an important factor affecting the stable operation of HVDC transmission,and the large error of R-C model in converter design and verification is a key factor that cannot be ignored.In view of the error of R-C model in oil paper insulation,it is generally believed that R-C model only considers the interface polarization charge and ignores the distortion of space charge to electric field,and charge transport models such as bipolar carrier model and ion current model are proposed.However,these charge transport models do not consider the influence of the difference of positive and negative charge mobility on the charge accumulation,which deviates greatly from the measured results.Therefore,the actual charge distribution and electric field distribution in oil paper insulation are still unclear,and the measurement of the important parameter mobility in ion current model remains research gap.In order to realize the accurate measurement of positive and negative charge mobility in oil paper insulation,a monopolar charge mobility measurement platform based on pulsed electro-acoustic with barrier layer was built.The platform’s applied DC voltage range is 0-10 kV polarity,high voltage pulse amplitude is 500 V,pulse width is 10 ns,and the system measurement resolution reaches 10 μm,it lays a foundation for accurate measurement of charge mobility of oil paper insulation.Based on the charge mobility measurement platform,the charge mobility in transformer oil and oil impregnated pressboard under different DC electric field intensities were measured by pulsed electro-acoustic with barrier layer.The results show that the order of magnitude of charge mobility in transformer oil is 1019,and the negative charge mobility is higher than the positive charge mobility.The proportional coefficient of the two increases with the increase of electric field strength;the order of magnitude of charge mobility in oil impregnated pressboard is 10-13,and the negative charge mobility is also higher than the positive charge mobility.The proportional coefficient of the two decreases first and then increases with the increase of electric field strength.The measured mobility is introduced into the ion current model for electric field analysis,and the results show that the error of the measured mobility simulation results is effectively reduced compared with the R-C model.The results show that the maximum deviation of ion current model in single oil channel model is 8.0%,which is 77.5%lower than that of R-C model;the maximum deviation of ion current model in average oil channel model is 90.9%,which is 231.4%lower than that of R-C model,which can be used to simulate the electric field.The accuracy and accuracy of electric field and charge simulation of oil paper composite insulation can be improved effectively.