Correlation between micro-structure and charge transport properties of polyethylene insulation under thermal ageing
In order to study the change rule of microstructure and dielectric properties of polyethylene(PE)materials under the action of thermal stress,PE samples were conducted accelerated thermal ageing tests at 90℃,and the microstructure and charge transport properties of the thermal aged PE samples were characterized by Fourier transform infrared spectrometer(FTIR),differential scanning calorimetry(DSC),X-Ray diffraction(XRD),high field conductivity(HFC)test,and isothermal surface potential decay(ISPD)tests.The results show that the thermal ageing process of PE samples can be divided into recrystallization stage and thermo-oxidative degradation stage.In the recrystallization stage,the crystallinity of the samples increases,the crystal structure tends to be perfect,the deep-trap density and deep-trap energy level increase,the carrier migration is restricted,and the threshold field strength of space charge injection increase.In the thermo-oxidative degradation stage,the crystallinity of the samples decreases,the crystal structure appears deterioration,the deep-trap density and deep-trap energy level decrease,the carrier mobility increases,and the threshold field strength of space charge injection decreases.Through the characterization of conductivity properties under different temperatures and field strengths,the variation rules of three parameters A,B,and φ in Steven Boggs'conductivity function were obtained.With the increase of ageing time,the φ and A increase at first and then decrease,and the B decrease at first and then remains unchanged,among which the material coefficient A is the most sensitive to thermal ageing.
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