Surface Charge Dynamic Behaviors Of Epoxy Resin Under Multi-physical Field

HVDC transmission technology will become the mainstream in the future to solve the issues of long-distance and large-capacity power transmission and the rational absorption of new energy sources.As an alternative of traditional HVDC transmission lines,DC GIL has advantages of long distance,large capacity,low loss and easy installation,which will play an increasingly important role in the field of HVDC transmission.However,during the operation of GIL,the accumulation of the surface charge on the basin-type insulator may cause the flashover along the surface,which threatens the stability and safety of the transmission system and even the entire power grid.In order to reduce the failure rate of the basin-type insulator,the charge characteristics of the epoxy resin material which GIL basin-type insulator is made of under multi-physical field have been studied in this paper.Taking into account the temperature rise during the operation of the basin-type insulator,the influences of different temperature and thermal conductivity on the surface charge characteristics of the high thermal conductivity epoxy resin material under DC voltage have been investigated.A method of surface modification called surface molecular structure control technology to suppress the surface charge accumulation on the epoxy resin has been proposed in the paper and the surface charge characteristics and flashover properties of the modified sample under the combination action of DC and pulse voltage.The research contents of this paper will provide theoretical and experimental basis for reducing the failure rate of the basin-type insulator and improving the operational stability of DC GIL.The main contents of this paper and the conclusions obtained are as follows:(1)The samples of high thermal conductivity epoxy resin with different content of BN were prepared by physical doping method and hot press forming method,and the surface charge dynamic characteristics of each sample under DC voltage at corresponding temperature after the same cooling time have been studied.The results show that at the same temperature,as the content of nano-BN increases,the surface charge dissipation rate of the sample becomes slower and then becomes faster,while the initial surface charge density first increases and then decreases.The study of the effect of different thermal conductivity and temperature on the surface charge characteristics of the samples indicates that for the same sample,the surface charge dissipation rate decreases and the initial surface charge density increases with the cooling time rise.And both of the deep and shallow trap energy levels of the sample decrease,while the density of deep traps increases and the density of shallow traps decreases.Moreover,the sample with higher BN content has higher thermal conductivity and faster temperature drop rate.The density of deep traps increases more and the surface charge dissipation rate decreases faster after the same cooling time..(2)Epoxy resin samples modified for different times were prepared by surface molecular structure modification system,and the effects of surface modification treatment on the relative dielectric constant,surface charge characteristics under combined DC and pulse voltage and flashover characteristics of samples have been studied.The results show that the relative dielectric constant of epoxy resin samples decreases firstly and then increases with the increase of modification time,and decreases to the lowest at 60 min.The carrier mobility of samples increases after surface molecular structure modification,and the trap energy level decreases,which inhibit the accumulation of charge on the sample surface and accelerate the surface charge dissipation process,remit the distortion of the surface electric field and effectively increase surface flashover voltage values of the sample.