Study On Conductance Nonlinearity Of Calcium Copper Titanate/Silicone Rubber Composite

HVDC transmission has the advantages of small energy loss,simple and rapid control of the line,and convenient power interconnection,which play an increasingly important role in the transmission field.The use of cables as direct current transmission lines for power transmission is convenient for trans-ocean transmission and can be used as underground cables to power the city without occupying urban space.These advantages have prompted the development of DC cables.However,due to the complex composite insulation structure of the cable accessories,there is a large conductance gradient between the constituent materials,which causes local electric field distribution to concentrate during operation,which resulting in a decrease in the insulation strength of the accessory.In order to solve the problem of the conductance gradient in the cable accessory,the doping modification of the accessory with the two-component addition liquid silicone rubber makes the electrical conductivity and the main insulation of the cable form a good match,in turn,improve the concentration of local electric field distribution caused by the conductance gradient.In this paper,calcium copper titanate nanoparticles and calcium copper titanate nanofibers were prepared by sol-gel method and electrospinning technique respectively.The calcium copper titanate silicates with different morphologies were uniformly dispersed into liquid silicone rubber by mechanical stirring.calcium copper titanate nanoparticles/silicone rubber and calcium copper titanate nanofibers/silicone rubber composite with different doping contents were prepared.The prepared inorganic filler phase and composite were characterized by micro-morphology and structure.The dielectric properties,electrical conductivity,DC breakdown performance and space charge performance of the composite media doped with different morphology were tested.Finally,the transient and steady-state electric field distribution of the accessory is analyzed by the electrical and thermal coupling through the COMSOL Multiphysics simulation software.As a result,it was found that the prepared calcium copper titanate nanoparticles had a particle diameter of about 300-500 nm,and the calcium copper titanate nanofibers had a diameter of about 400 nm and a fiber length of 5-8um.As the doping concentration of the inorganic filler increases,the dielectric constant of the composite also increases.The dielectric constant of the calcium copper titanate nanoparticle/silicone rubber composite with the same doping concentration is lower than the dielectric constant of the calcium copper titanate nanofiber/silicone rubber composite.The conductivity of the composite medium increases with the increase of the doping concentration of the inorganic filler,and the conductivity of the calcium copper titanate nanofiber/silicone rubber composite increases more obviously.At the same time,the DC breakdown strength of the composite medium decreases as the inorganic filled phase increases.The depolarization process of the composite indicates that the space charge dissipation rate is positively correlated with the concentration of the inorganic packed phase.Finally,the simulation results show that the electric field concentration of the root of the stress cone is obviously improved with the increase of the concentration of the inorganic filling phase,but the improvement effect of the calcium copper titanate nanofiber/silicone rubber composite is more effective.3vol.% calcium copper titanate nanofibers/silicone rubber composite can achieve good improving effect in steady state and transient process.