Polarization Characteristics Of Oil-Pressboard Insulation Under The DC Polarity Reversal

Converter transformer plays an important role in high and ultra high voltage DC transmission system,the reliability of converter transformer determines the safety operation of the whole system.In the operation process valve side of converter transformer main insulation not only endure the impact of AC voltage and overvoltage,and subjected to a polarity reversal voltage.In order to reduce the high fault of converter transformer in operation rate,improve the converter transformer insulation performance,it is necessary to do research the oil-pressboard insulation polarization characteristics under the polarity reversal voltage,it has academic value and engineering significance to study this problem.This paper designed a set of dual current signal detection system.According to converter transformer insulation structure characteristics,designed the test model and three electrode system,and used the existing laboratory equipment to build the polarity reversal voltage test platform.The treatment of transformer oil and oilimpregnated paperboard was completed,and the test sample was made.The direct polarity reversal voltage was used to study the oil-pressboard insulation.The polarization characteristics of the oil-pressboard insulation under polarity reversal voltage are discussed based on the experimental data.Based on this study,The influence of oil gap electric field on insulation characteristics of oil-pressboard insulation is explained from the angle of electric field distribution.The results show that when polarity reversal voltage is completed,polarization current of oil-pressboard insulation samples attenuates according to exponential function of power function of time,but does not follow index function;the relation between steady-state current and applied voltage obeying Ohm's law.Under the same voltage amplitude,the positive polarization current value and the negative polarity current value are asymmetrical and have obvious polarity effect.The above polarization characteristics confirm that the insulation resistance of oil-pressboard insulation is nonlinear.The electric field of oil gap in oil-pressboard insulation can continue to a higher level with the change of voltage applied time and polarity.