温度梯度对直流盆式绝缘子表面电荷积聚特性的影响OA

With the continuous development of the power grid scale and renewable energy,flexible high voltage direct current(HVDC)transmission technology has gained global wide attention.The DC gas insulated switchgear/transmission line(GIS/GIL)have advantages of low loss,large capacity,and easy grid interconnection,which become a key link in HVDC transmission systems.However,surface charge accumulation on basin insulators will degrade the interfacial insulation performance,posing a key technical challenge of insulation design.Under regular serving conditions,the current thermal effect will create high temperature in the central conductor,which generates radial temperature gradients across insulators.The temperature gradient significantly influences the insulator's bulk conductivity distribution and surface charge accumulation,which may further reduce flashover voltage along the gas-solid interface.At present,few studies systematically examine how temperature gradients affect surface charge accumulation,which significantly hinders the insulation design of DC GIS/GIL under thermal gradients. This study first constructed a surface charge measurement platform with controllable temperature gradient.It enabled the temperature difference(ΔT)between HV conductor and grounded electrode to be adjusted from 0℃ to 63.4℃.Then the surface charge distributions were tested under positive DC voltage and various temperature gradients.The results showed that the temperature gradients did not alter the surface charge accumulation pattern.A bipolar-charge distribution appeared on insulator surface:positive charges concentrated between the HV and grounded electrodes,while negative charges mainly distributed near the grounded electrode.As ΔT increased from 0℃ to 63.4℃,the distribution area of positive charges shrank gradually,with average density decreasing from 2.09 µC/m2 to 1.05 µC/m2.In contrast,the distribution area of negative charge expanded significantly,with average density rising from 2.39 µC/m2 to 5.77 µC/m2(a 141%increase).Absolute maximum charge density increased from 8.21 µC/m2 to 16.24 µC/m2.These findings demonstrated that temperature gradients substantially enhanced surface charge accumulation on insulators. To analyze how temperature gradients affect the dominant accumulation pathways of surface charge,a multi-physics field simulation model coupling electric,thermal,and gas flow fields was further developed.This model accounted for the temperature-dependent bulk conductivity of the insulator,as well as the charged particle's diffusion,migration and recombination processes driven by the electric and flow fields in gas side.The results showed that under no and low temperature gradients,the bulk conductivity was small,resulting in a relatively small bulk conduction current,so the surface conduction current was the dominant accumulation pathway for positive charges.As the temperature gradient increased,the dominant accumulation pathway of positive charges gradually changed from surface conduction to bulk conduction due to the surge of insulator bulk conductivity.And the difference between bulk current and surface current became smaller,resulting in a reduction of positive charge density.The dominant accumulation pathway of negative charges was always surface conduction.The increase in temperature gradient caused the electric field near the ground electrode to surge from 1.05 kV/mm to 2.78 kV/mm,which led to a significant increase in the surface current and negative charge density near the grounded electrode. Overall,large temperature gradients will cause an electric field surge near the grounded electrode,further aggravating the surface charge accumulation.This may result in a greater risk of flashover occurring along the gas-solid interface.Therefore,it is necessary to explore insulating materials with low temperature coefficients of bulk conductivity in DC GIS/GIL,which makes the electric field and surface charge accumulation to be reduced.Meanwhile,components such as shields and flanges in the vicinity of the grounded shell need to be particularly designed to maximally relax the electric field distortion.