Study On The Preparation And Electrical Properties Of MgO/LDPE Nano Composites

In recent years, with the rapid development of EHVDC transmission indomestic and it makes the increasing requirement for power system to EHVDCtransmission cable. In the DC electric field, the space charge which easily formedin traditional cable material could distort the distribution of the electric field,made the polymer aging and even cause the insulation breakdown. According toreports, a small amount of nano-MgO that was loaded in LDPE could effectivelyrestrain the gather of space charge, and satisfied the requirement of EHVDCtransmission. In this paper, we investigated the calcined process of Mg（OH）₂, thesurface treatment technology on MgO, the blended technology for MgO/LDPEcomposite, and the mechanical properties, volume resistivity, breakdown fieldstrength, space charge of nano composite.The calcination process step was researched by using orthogonal method.According to the two-step calcination scheme, we calcined the homemadeMg（OH）₂, next measured the particle size distribution of MgO powder, nextanalysised the data by SPSS software, ultimately determined the calcinationprocess step. Besides combined with XRD, we compared the influence of two-step calcination and traditional calcination on the particle size of MgO powder.The results showed that the particle size of MgO powder was less than traditionalcalcination, which was made by two-step calcinations. Besides the particle sizedistribution was uniform.All the coupling agent process was confirmed. We modified the MgOpowder with coupling agent （KH-540, KH-550, KH-570, NDZ-105, XLS typerare earth coupling agent）, next confirmed the modification temperature ofcoupling agent （KH-540, KH-550, KH-570, NDZ-105） and the dosage of XLStype rare earth coupling agent. Ultimately combined with SEM test, we chose thesuitable coupling agent for surface treatment of MgO powder. The results showed that when modification temperature was55℃, the treatment effect of MgOpowder that was modified by KH-550was best. Moreover the particle size ofMgO powder was about50nm, evenly dispersed.The preparation technology of MgO/LDPE nano composite was researchedby using orthogonal method. According to blend scheme, we prepared theMgO/LDPE nano composite material, measured the thin sections of composite byoptical electronic microscope. Next classified the entire composite sample basedon the particle size of MgO particles and dispersion of the LDPE. Ultimately, wedetermined the blending process by analyzing the data. The results showed thatwhen the blending condition was150°C,60r/min,0.25h, the MgO/LDPE nanocomposites prepared had the best effect, the size of MgO particle was60-90nm,scattered evenly in LDPE.The performance of MgO/LDPE nano composite material was investigatedthrough SEM, tensile test, volume resistivity, dielectric strength and PEA testmethods. The result showed that when MgO content was2wt%, EVA content was6and9wt%, the material mechanics and electricity performance of MgO/LDPEcomposite were best, and effectively restrained space charge in the MgO/LDPEcomposite. At this time, the charge density in cathode of composite materials was17.4C/m3, the charge density in anode was13.4C/m3.