Conductivity Modification Of Graphene Oxide/Epoxy Resin Composites And Application In Valve Side Bushing Of Converter Transformer

Valve side bushing of UHV converter transformer is the key equipment in UHVDC transmission project,which plays a vital role in the safe operation of UHV converter station.The temperature gradient of valve side bushing of converter transformer makes the conductivity distribution of epoxy core deviate,which leads to the electric field distortion of epoxy core.In this thesis,nano graphene oxide particles were used to modify the epoxy resin,in order to explore the DC conductivity and charge transport characteristics of the epoxy composite under electric-thermal compound field.Using neat epoxy resin and graphene oxide/epoxy resin composite material as the main insulation of the valve side bushing of converter transformer,the characteristics of electric heat distribution and the effect of electric field regulation of the valve side bushing epoxy core of ±800 kV UHV converter transformer are analyzed,in order to provide experimental basis and theoretical support for the design of valve side bushing of UHV converter.The main research contents and conclusions are as follows:(1)Epoxy resin composites with different nano graphene oxide content were prepared by physical doping method and hot pressing method.The conductivity characteristics of the composites from 20 ? to 80 ? were obtained based on the controllable temperature conductivity test platform.With the increase of the content of graphene oxide,the temperature coefficient and activation energy of the conductivity of the composites decreased.The results of conductivity at different temperatures show that the epoxy composite with 0.1 wt% graphene oxide has the lowest temperature conductivity and activation energy.(2)Based on the data processing method of surface potential decay,the trap energy level distribution of neat epoxy resin and graphene oxide/epoxy resin composite was calculated.The results show that the introduction of graphene oxide increases the shallower trap density and decreases the deeper trap density at the same temperature;with the increase of temperature,the deep trap density decreased and the shallow trap density increased.The introduction of graphene oxide results in the increase of shallower trap density at the same temperature,which makes carriers need more hopping to complete the conductivity process,so the temperature coefficient and activation energy of conductivity of graphene oxide/epoxy composite decrease.(3)According to the temperature-conductivity characteristics of neat epoxy resin and graphene oxide/epoxy resin composite,the valve side bushing of ± 800 kV UHV converter transformer is simulated,and the radial conductivity distribution and electric field distribution of the valve side bushing of converter transformer are analyzed.The simulation results show that the axial conductivity distribution of the epoxy core with graphene oxide/epoxy composite is more uniform,and the electric field distribution of the epoxy core is more uniform,and its maximum field strength is about 30% lower than that of the traditional bushing with neat epoxy.Compared with the traditional bushing,graphene oxide/epoxy resin composite is used as the epoxy core of the valve side bushing of converter transformer,which effectively improves the electric field distribution of the valve side bushing.