Non-linear Conductivity Characteristics Of Epoxy Resin Composites Filled With SiC Particles

High voltage direct current(HVDC)power equipment is an important part of the system of long-distance and large-capacity power transmission and renewable energy consumption.However,the electric field distortion is widely existing in key equipment of HVDC transmission,not only causing partial discharge and aggravating the aging of insulation materials,increasing the probability of failure of the composite insulation system,but also bringing challenges to designing and manufacturing HVDC equipment and limiting the development of HVDC transmission grade and capacity.Conventional measures to improve the electric field distribution have their own limitations.It is proposed in this paper that using composite materials with non-linear conductive characteristics can smartly smooth the non-uniform electric field.With the purpose of providing experimental data support for the design of HVDC transmission equipments,this paper takes HVDC transmission equipment as application background and studies the non-linear characteristics of the epoxy resin(EP)/SiC composite materials and their effects on regulating the distribution of electric field when they are in HVDC basin spacer and converter transformer bushing.The main contents of this paper and the conclusions obtained are as follows:(1)The epoxy resin(EP)/SiC composite samples with different contents and different SiC crystal forms were prepared by physical doping method and hot press forming method.The non-linear characteristics of each sample under different temperature was studied.The results show that at the same temperature,as the content of micro-SiC increases,the non-linear characteristics of EP/SiC composite samples become stronger,which is characterized by the increasing non-linear coefficient and the decreasing non-linear threshold.The study of the effect of different SiC crystal forms on the non-linear characteristics of EP/SiC composite samples indicates that for the same temperature,SiC content and the electric field strength,the non-linear characteristics of EP/β-SiC composite samples are much stronger than those of EP/α-SiC composite specimens,because rod-shaped β-SiC at the same content is more li ely to form a percolation channel than spherical α-SiC.A study on different temperatures’ influence on non-linear characteristics of composite samples shows that when the content is low,the conductive mechanism is mainly the thermal shock jump conductance and the conductivity increases significantly as the temperature increases;when the content is high,SiC particles in the composite material contact each other to form a perfect percolation network,and the sensitivity of the conductivity to temperature decreases.(2)The non-linear epoxy resin composites were used to replace the common epoxy resin,and researched its effects on regulating the distribution of electric field on HVDC basin spacer and HVDC converter transformer bushing.The results show that the application of non-linear conductive epoxy composites can reduce the maximum electric field strength amplitude and uniform the electric field distribution along the spacer.When the bushing core is made of non-linear conductivity epoxy resin composites,the field distortion at the flange is improved,which also decreases the field strength in the SF6 and oil.Doping micro-SiC to the epoxy resin matrix to obtain non-linear conductance greatly improves the electrical conductivity of the epoxy resin composite,which will cause higher power loss during operation,but compared with the power loss of the guide rod,increasing loss of the non-linear spacer and the bushing is negligible.