Study On Accelerated Thermal Aging Test And Life Prediction Of Liquid Silicone Rubber In Cable Accessories

In recent years,the new HVDC based on voltage sourced converter technology is developing rapidly,which makes XLPE DC cable a great prospect for development in electric power transport engineering.Operating experience shows that compared with cables,the cable accessories' failure probability is higher in the operation.Silicone rubber is the main insulation materials of XLPE DC cable accessories,it is severely affected by the heat.Therefore,the study of silicone rubber's mechanism under the effect of thermal oxidative aging,plays an important role to the safety operation of the accessories.First of all,this dissertation introduces the preparation of the samples,the way of accelerated thermal oxidative aging,and the experiment method for the test of macro parameters(electrical properties,mechanical properties)of silicone rubber samples.Experiment results show that along with the increase of aging time,the silicone rubber samples' macro parameters changed obviously,the breakdown voltage(the breakdown field strength),the hardness and the elasticity modulus of silicone rubber samples increased;But the tensile strength and elongation at break drastically decreased with the increase of aging time.Secondly,in order to study the thermal oxidative aging mechanism of silicone rubber,in this dissertation,Thermo Gravimetric Analysis(TGA),Energy Dispersive X-ray Spectrum(EDX),total reflection attenuation spectrum(ATR-FTIR)and Thermally Stimulated Current(TSC)of silicone rubber samples were tested.The experiment results show that in the process of thermal oxidative aging,silicone rubber materials mainly occurs the siloxane polymer crosslinking reaction.Under the action of heat and oxygen,the organic groups(CH3 etc)of polysiloxane break offfrom the main chain,and form a new Si—O—Si junction at the same time.This reaction leaded to the decreasing content of C element,the increasing content of O element and rising absorption peak value of Si—O—Si,declining absorption peak value of Si—CH3 and O—Si(CH)2—O in the silicon rubber system.Finally,this dissertation studied the stress relaxation properties of silicone rubber materials under the combined action of heat and mechanical force,and used the stress relaxation properties as the index of aging property change to predict the life of silicone rubber.Based on the test of thermal accelerated aging temperature and the stress relaxation properties of silicone rubber,the life prediction model for silicon rubber material is given,and predict the life of the silicone rubber material by this model.Laying a foundation of predicting life of the DC cable accessories.