Study On Space Charge And Corona Aging Characteristics Of Fluorinated Polyethylene

With the rapid development of high-voltage direct current transmission in China,polyethylene cables have been widely used in HVDC transmission systems due to their excellent mechanical and electrical properties.However,under the action of HVDC electric field for a long time,it is easy to accumulate space charge in polymer cable.Space charge leads to serious distortion of electric field distribution in materials,which causes a series of problems such as aging and breakdown of materials.The linear low-density polyethylene material was used as the research object,and the material was surface-treated by direct fluorination technology.Fourier transform infrared spectroscopy and scanning electron microscopy were used to analyze the chemical composition and micromorphology of samples before and after fluorination.The results showed that a large number of hydrogen atoms in the surface layer are replaced by fluorine atoms by direct fluorination technology,and the surface morphology of fluorinated polyethylene samples become rough.The characteristics of charge distribution in polyethylene samples were studied based on electroacoustic pulse method,and the surface charge dynamic characteristics of the samples were studied by isothermal surface potential decay method.The trap levels and trap densities in the surface layer of the material were calculated and the effect of direct fluorination on the distribution of trap levels in the polyethylene material was analyzed.The results show that the fluorination treatment forms a large number of traps on the sample surface,thus making the sample surface capture more charges and form a shielding layer,at the same time increasing the potential barrier of charge injection.Therefore,fluorinated polyethylene samples can effectively inhibit the space charge injection and accumulation.The aging test of polyethylene samples before and after fluorination was carried out by using a needle-plate corona discharge device,and the surface composition and micromorphology of the samples after corona aging were analyzed.The results show that,under the same corona aging conditions,the newly generated O-H bonds and C=O bonds in the fluorinated samples are less than those in the non-fluorinated samples,which indicates that the direct fluorination technology can improve the corona resistance of polyethylene samples.The C-F bond has shorter bond length and higher bond energy than the C-H bond,and the radius of fluorine atom is larger than that of hydrogen atom,thus reducing the free volume of the sample.Therefore,the surface of fluorinated polyethylene samples is more difficult to destroy.