Effect Of Conductor Roughness On Charge Accumulation At The Gas Solid Interface Of DC GIL Spacer

Under the background of "double carbon",high power and long distance high voltage direct current(HVDC)transmission technology has been developed rapidly,but the problem of charge accumulation at the gas-solid interface of spacers in DC GIS/GIL has seriously restricted the development process of HVDC transmission technology.The electric field distortion caused by the rough surface of the metal conductor inside the DC GIS/GIL directly affects the charge accumulation phenomenon at the gas solid interface of the spacer.Therefore,it is important to study the effect of conductor roughness on the charge at the gas-solid interface of spacers inside DC GIS/GIL.In this paper,a horizontally placed GIS coaxial structure electrode temperature control system based on oil circulation is established to realize simultaneous loading of 50 kV DC voltage and 50℃ high temperature on the high voltage electrode.The effects of high voltage electrode roughness,high voltage electrode temperature and DC voltage polarity on spacer surface potential were tested under SF6 gas environment of 0.1 MPa.It is found that the higher the electrode roughness,the more the gas-side source charge;without temperature gradient,the insulator surface accumulates only homopolar charge;when there is temperature gradient,the solidside charge injection increases,the gas-side charge migrates to the spacer surface more easily,the spacer surface is still dominated by homopolar charge but anisotropic charge appears,and the charge on the upper half of the spacer surface is lower than that on the lower half;there is polarity effect,the charge on the spacer surface under negative polarity DC stress is higher than that when positive polarity stress is applied,and the anisotropic charge distribution on the spacer surface shows a higher randomness when there is a temperature gradient.The surface morphology of the experimental high voltage electrode was observed,and the electric field distribution on the surface of the experimental high voltage electrode was calculated by finite element simulation.The research results show that the surface of the electrode is a continuous multi-protrusion structure,the high field distortion is located at the top of the protrusion,and the low-field area is located at the depression,that is,the electric field intensity distribution is consistent with the distribution of the protrusions and depressions.The semi-ellipse structure is used to simulate the micro-convexities on the electrode surface,and the effects of the protrusion spacing,protrusion height and protrusion width on the electric field distribution on the multi-protrusion surface are studied by finite element simulation.The results show that as the ratio of protrusion height to width increases,the close proximity electrostatic effect between the protrusions is enhanced and the electric field intensity on the protrusion surface is suppressed;as the protrusion spacing increases,the close proximity electrostatic effect between the protrusions is weakened.For a electrode of a certain length,the reduction of the distance between the protrusions will inevitably lead to the increase of the number of protrusions.The competitive relationship between the close-range electrostatic shielding effect and the number of protrusions was studied by means of theoretical calculations,which show that when the ratio of protrusion height to width is small,the strength of the close proximity electrostatic effect between protrusions ultimately determines the amount of gas-side charge from microdischarge;while when the ratio of protrusion height to width is high,it exhibits a "segment-dominant" characteristic,and there is an optimal protrusion spacing to minimize the amount of gas-side charges brought by the microdischarge.