Research On MV/HV Cable Manufacturing Technology And Material Properties Of UV-photoinitiated Crosslinking Polyethylene

UV-photoinitiated crosslinking polyethylene technology is a kind of cable manufacturing process that the melted and transparent polyethylene is crosslinked by the irradiation of high-intensity UV source.Compared to the traditional peroxide crosslinking method,UV-photoinitiated crosslinking method has the advantages of fast crosslinking rate,energy saving and environmental protection,and nonthermosensitive material.It has been successfully applied in the field of low voltage power cable manufacturing.Under the support of the 863 Project,the UVphotoinitiated crosslinking technology for producing medium and high voltage power cables and the related material properties of UV-photoinitiated crosslinking polyethylene are studied in this paper.According to the insulation structure of medium and high voltage power cables,an integrated crosslinking process was designed that insulation layer and shielding layer is crosslinked through UV irradiation and peroxide crosslinking respectively.A “2+1” extrusion mode was proposed that conductor shielding and insulation are extruded first,and then extrude the insulation shielding after the insulation was fully crosslinked through UV irradiation.An irradiation system using UV mercury lamps and UV LED arraies in combination was proposed according to the UV radiation dosage for fully crosslinking large-thickness insulation and the requirement of avoiding thermal aging due to high temperature.The specific process of integrated crosslinking process was designed.Based on the measurement of the thermal physical properties of the insulation and shielding materials,the temperature field distribution of the cable during processing was calculated by simulation software.The simulation results show that the insulation and shielding can be maintained within a reasonable temperature during processing,and both can achieve sufficient crosslinking degree.A long-life and high-stability UV electrodeless curing lamp was developed based on the irradiation requirement for large thickness insulation to solve the problem of rapid attenuation of the light intensity of conventional UV mercury arc lamp.Combination with the characteristics of elliptical focusing and microwave resonance,a co-simulation analysis of geometric optics and electromagnetics was used to solve the difficulty in the structural design of microwave resonator.The experimental results show that the UV electrodeless curing lamp prototype has a reasonable UV emission spectrum and irradiance distribution,and has higher irradiation crosslinking efficiency than the traditional UV mercury arc lamp,which means that UV electrodeless curing lamp is more suitable as UV mercury lamp in the integrated crosslinking process.The differences in crystallinity,mechanical properties and water tree-aging performance between UV-photoinitiated crosslinking polyethylene and peroxide crosslinking polyethylene were studied.The results show that the use of linear low density polyethylene as the base resin is the main reason for the higher crystallinity,melting temperature,and mechanical strength of the UV cross-linked polyethylene.Through the analysis of strain hardening ability,it was confirmed that the intermolecular tie molecule chains can effectively hinder the infiltration of water molecules into the material under the action of electric field.The crosslinking bonds and short branches of linear low density polyethylene can significantly increase the density of tie molecule chains between the lamellaes,so that UV-photoinitiated crosslinking polyethylene and material with higher crosslinking deree have the better water tree resistance.In addition,dynamic thermomechanical analysis(DMA)confirmed that the crosslinking bonds can increase the β relaxation resistance,which can buffer the force of water molecules impact on the amorphous phase of the material under electric field,so that the growth rate of the water tree can be restrained.The electrical properties of UV-photoinitiated crosslinking polyethylene for high voltage DC cable insulation were studied.Compared with peroxide crosslinking polyethylene,UV-photoinitiated crosslinking polyethylene has lower electrical strength and higher electrical conductivity and conductivity dependence,which may be due to the residual UV crosslinking by-product benzopinacol with larger molecular weight.The α relaxation of UV-photoinitiated crosslinking polyethylene caused the temperature of its pyroelectric peak rise significantly,which made its space charge characteristics better than peroxide crosslinking polyethylene at the normal temperature of cable insulation.In addition,results showed that UVphotoinitiated crosslinking polyethylene can significantly inhibit its conductivity and conductance temperature dependence after grafing maleic anhydride.The reason for this phenomenon is that grafting maleic anhydride can introduce deep trap so that the charge injection and carrier transport could be suppressed.The research results in this paper show that it is feasible to manufacture medium and high voltage power cable using UV-photoinitiated crosslinking polyethylene technology.The insulation produced by this process has excellent water tree resistance performance for medium voltage cable and DC performance for high voltage DC cable.