The Study Of Oil-film Insulation State In Impact Capacitor Based On Polarization Depolarization Current Detection

The impulse capacitor is installed in the neutral bus of HVDC transmission project,and it plays the role of absorbing lightning impulse or other grounding fault currents.The long time operation will easily lead to the decline of its insulation performance under the action of thermal and electrical aging.At present,oil film insulation is widely used in impulse capacitors,polypropylene film as solid insulation,benzyl toluene as an impregnant.Good oil film insulation is conducive to reliable operation of impulse capacitors,and ensures safety and stability of HVDC transmission system.Therefore,it is necessary to detect and study aging state of oil film insulation.In this paper,the polarization depolarization current of oil film insulation with different aging degree is mainly studied.An oil film insulation model device for shock capacitor is made.The thermal aging platform and the electric aging platform are used to age the oil film.Gas components in oil with different aging degrees were tested.The surface morphology of the films under different aging conditions is observed and analyzed.The polarization depolarization current of oil film insulation with different aging degree is measured.the equivalent relaxation branch number and the first grade branch parameter of oil film insulation with different aging degrees are obtained by using the extended Debye model and matrix pencil algorithm,The experimental results show that the amplitude of polarization depolarization current increases significantly with the increase of oil film aging.The equivalent capacitance of the oil film interface increases with a small amount of gas generated between the oil film and the surface roughness.The aging degree of oil film will also deepen under repeated impact.In the extended Debye model,the resistance value of the first branch parameter decreases with the deepening of the aging degree,and the capacitance value is opposite.The test results show that the polarization depolarization current method can effectively distinguish the insulation state of the oil film with different aging degree.As a nondestructive testing method,it can be used to detect and analyze the insulation state of the oil film composite insulating medium.