Study On The Influence Of Hydrostatic Pressure On The Oil-paper Discharge Characteristics And Its Mechanism

With the development of social economy and the growing of power grid transmission capacity,the wide application of large power transformers makes oil paper insulation operate in different oil hydraulic environments.Understanding the influence of hydrostatic pressure on the operation and decaying of oil-paper insulation is of great value to the optimization design,reasonable operation,lightweight and miniaturization of transformers.Basing on the developing of whole sealing,pressure adjustable and tip fully shielded oil-paper partial discharge testing platform,this paper researched the effect of hydrostatic pressure on the discharge of typical defects of oil-paper insulation.Recorded the experimental phenomenon,analyzed the mechanism and verified the new theory.The main research works are as follows:A tip completely shielded oil-paper partial discharge test platform with a whole sealing and pressure adjustable tank was established.An experimental oil tank with a piston in the oil conservator,a group of shielding kits and a set of composit structure insulation support were designed.Based on this,the development law of the oil-paper surface discharge under tangential electric field and different hydrostatic pressures was researched with needle-plate model.The developing process of the discharge parameters with time and different pressures were acquired.It was discovered that the developing law of maxmum discharge is different from that of other parameters.To explain the mechanism of hydrostatic pressure influencing the oil-paper surface discharge,the combination of bubble and paperboard under different pressure was analyzed.The sparks and white marks on the pressboard surfaces were photographed,and the condition leading to the appearance of white mark on pressboard under tangential electric field was obtained.The influence of hydrostatic pressure on the generating of white mark was analysed.Partial discharge development of oil-paper insulation under normal electric field and different hydrostatic pressures was researched with the needle-plate testing model.Under step-up voltage it was found that the development of discharge is very rapid when the hydrostatic pressure is very low.The mechanism of hydrostatic influence on discharge was analyzed.The trends of discharge parameters varying with time under different hydrostatic pressures were compared.The hydrostatic pressure ranges under which gas,spark and white spot phenomena occur were summarized.The mechanism of hydrostatic pressure influencing the oil-paper insulation was verified by the gas phenomena.Through the curves from the test under constand voltage,the influence of hydrostatic pressure on discharge parameters were further clarified.The column-plate surface discharge model was adopted to explore the surface discharge of oil-paper insulation under oblique electric field and different hydrostatic pressures.Under step-up voltage,it was found that the probability of breakdown at high altitude areas is high if the discharge is initiated.It was discovered that there were stable periods in the developing process of partial discharge under step-up voltage,and the characteristics and reasons of this phenomenon were figured out.The mechanism of hydrostic pressure influencing the column-plate model surface discharge was analysed and verified by the gas phenomenon before breakdown.Through stable voltage test,the mechanism of hydrostatic pressure influencing the column-plate oil-paper insulation surface discharge was further verified,and the nondestructive testing criterion of pressboard was proposed through the test result.