The Effects And Mechanism Of Electrode Material On The Breakdown Voltage Of Liquid Dielectric

As a commonly used power system liquid dielectric, transformer oil's insulating properties are closely related to safe operation of the power system. Electrode material may affect theinsulating properties of pure liquid dielectric.Electrode will inject some charges into liquid dielectric under the influence of voltage which may disturb the original distribution of the electric field and affect the propagation of streamer. Different electrode material has different space charge injection mode and injection volume which may result in the differences in insulating properties of liquid dielectric.In addition, the space charge injection ability of electrode material in different liquid dielectric maybe different. However, the researchs on the influence of electrode material to the insulating properties of liquid dielectric were not enough and did not draw a universal conclution.Therefore, this article has explored the impact of electrode material to the insulating properties of liquid dielectric.We chose propylene carbonate as the liquid dielectric, built the corresponding space charge measurement platform and measured the switching impulse breakdown voltage of propylene carbonate before and after nanoparticles modified under different electrode materials(copper, aluminum and stainless steel). What's more, we measured the electric field and space charge distribution between the gap of plate electrodes under the same condition as well. The test results are as followed:(1) Electrode material has an influence on the breakdown voltage of propylene carbonate. The switching impulse breakdown voltage of pure propylene carbonate between stainless steel electrodes issignificantly higher thanthose between copper electrodes and aluminum electrodes. The breakdown voltage of propylene carbonate between copper electrodes is higher than those between aluminum electrodes as well.(2) When propylene carbonate is modified by nanoparticles, its breakdwon voltage under eachelectrode materialincreases. But the breakdwon voltage under different electrode material is still different.(3) Whenpropylene carbonateis used as the liquid dielectric, the space charge injection ability of aluminum, copper and stainless steel electrodes isin descending orderandthe electric field distortion rate between plates isin descending order too.(4) The space charge injection ability of the electrode material we chose decreases when propylene carbonate is nano-modified.The electric field distortion rate between plates also decreases when propylene carbonate is nano-modifiedIn order to cover the shortage of transformer oil which has a low Kerr constant, we extended plates and chose array photodetector to build the corresponding space charge measurement platform.We used aluminum and stainless steel as the electrode materials of circular plate electrode. Then wetestedthe switching impulse and lighting impulse breakdown voltage of transformer oil and transformer oil-based nanofluid between the electrodes we chose. We measured the electric field and space charge distribution in transformer oil as well. The test results are as followed:(1) The impulse breakdown voltage of transformer oil between stainless steel electrodes ismuch higher than that between aluminum electrodes.(2) The addition of Al2O3 nanoparticles to modify transformer oil can enhance its insulation strength between aluminum electrodes. But there isno improvement of insulation strength between stainless steel electrodes though the transformer oil was modified by nanoparticles.(3) When we use transformer oil as the liquid dielectric, the amount of space charges injected from stainless steel and aluminum electrode isfew at the early time that voltage effected. When voltage was applied more than 1500 ?s, the amount of space charges injected from aluminum electrode was more than that of stainless steel electrode so that the electric field distortion rate between aluminum electrodes was higher than that between stainless steel electrodes.(4) The space charge injection ability of aluminum electrode is significantly inhibited when transformer oil is modified by nanoparticles. For this reason the electric field in nano-modified transformer oil ismore uniform than that in pure transformer oil. Though the space charge injection ability of stainless steel electrode is inhibited, considered to its low space charge injection ability, the electric field distortion rate in nano-modified transformer oil and pure transformer oil is nealy the same.We think that different electrode material has different space charge injection ability which results in different electric field distortion rate between plates that causes the differences in impulse breakdown voltage. Adding some Al2O3 nanoparticles to liquid dielectric can increase the density and depth of "trap" near nanoparticles in liquid which enhance the probability of "trap" capturing charges. "Trap" can capture the fast moving charges and remain them in the vicinity of the electrode which weakening the electric field near the electrode. Thus, the space charge injection from electrode is suppressed, the electric field between plates is uniformer and the breakdown voltage increaseswhen liquid dielectric is nano-modified.