Research On Dielectric And Space Charge Characteristics Of Low Density Polyethylene/titanium Dioxide Nanocomposites Under Thermal Aging

The excellent mechanical and electrical properties of polyethylene nano dielectric has been widely recognized,including good tensile strength,high breakdown strength,low conductivity,uniform electric field distribution,and inhibition of electrical tree growth,which has potential to become the insulation material of high voltage direct current cable,reducing space charge effect and improving DC voltage level.In the process of operation,the cable will be subjected to the electrical,thermal and mechanical stress,leading to the deterioration of the insulation material and threatening the reliability of power transmission.In order to realize the popularization and application of polyethylene nano dielectric in DC cable,the mechanical and electric properties of which under operation environment should be demonstrated,analyzing nanoparticle doping whether accelerate aging of polyethylene or not.Therefore,the physical and chemical properties,dielectric properties and space charge characteristics of LDPE/TiO₂ nanocomposites were studied in this paper.The main work of this paper is as follows:?1?The TiO₂ nanoparticles modified by MDOS coupling agent has good compatibility and dispersibility in LDPE.The nanoparticles doping not only improve the crystallinity of polyethylene and thermal stability,but also introduce a number of traps,improve the breakdown electric field of polyethylene;thermal aging changes the micro morphology of samples,resulting in a large number polar groups such as hydroxyl,carboxyl and carbonyl groups;the micro morphology,content of polar groups,crystallinity and breakdown are closely related to the doping concentration;these results showed that the LDPE/TiO₂ composite has an anti-thermal ageing ability.?2?The basic shape specimen of dielectric constant and dielectric loss changed regularly with aging time;the main reason for the loss of low frequency,medium frequency and high frequency dielectric loss are the loss of conductivity,the polarization of the steering,and the deep trap relaxation loss;thermal aging did not affect the activation energy of low frequency loss peaks,but the nanoparticles filler reduced the activation energy of low frequency loss peaks;TiO₂ crystal has negative temperature coefficient and wide "softening temperature zone",which is the main reason for ?? decreases with increasing temperature.?3?The physical and chemical properties and dielectric parameters tests showed that the LDPE/TiO₂ composite had a certain anti-thermal ageing ability.Particularly,the composites exhibited the best anti-thermal ageing ability when the doping mass fraction was 0.5%.TiO₂ nanoparticles act as "connection points",reducing the movement of molecular chain,increasing the crystallinity of composite materials,improving the microstructure density,and delaying oxygen intrusion to destruct the macromolecular.At the same time,it also act as "heat transfer points",increasing the thermal conductivity of composite.The heat can be quickly transferred out of the material,reducing internal local overheating area.?4?LDPE/TiO₂ composites can inhibit the space charge before and after thermal,especially,the composites had the best inhibitory effect of space charge when the doping mass fraction is 1%;Nanoparticles doping changed polyethylene dielectric constant and electron affinity,strengthen the anti-interface electric field.Therefore,the electron?hole?injection barrier was improved,reducing the source of homocharge.At the same time,the interfacial region contain large number of traps,reducing carrier mobility,strengthening the neutralization of positive and negative charge,and weakening the ionization of impurities.Consequently,the source of heterocharge is reduced.