纳米TiO2对直流电缆用XLPE介电性能的影响

Effect of nano-TiO2 on Dielectric Properties of XLPE for HVDC Cable

为探索提升高压直流电缆用交联聚乙烯直流介电性能的方法,采用熔融共混法在直流电缆用交联聚乙烯基体中添加微量(质量分数0.1%、0.5%、1%)纳米TiO2制备得到XLPE/TiO2纳米复合介质,并通过纳米粒子表面偶联剂处理对比研究了表面改性对XLPE/TiO2介电性能的影响。采用SEM观测纳米粒子的分散性,测试了XLPE和XLPE/TiO2的结晶度、电导率温度特性、空间电荷注入特性和直流击穿场强。结果表明,采用偶联剂进行表面处理能够改善纳米粒子的分散性,在直流电缆用XLPE中直接添加微量纳米TiO2能够增大结晶度、电导活化能和直流击穿场强,降低电导率,抑制正电荷的注入,而添加经过偶联剂处理的纳米TiO2可使这些影响更加显著。分析认为,结晶度的增大是由于纳米粒子的成核作用,而偶联剂处理使得粒子与基体结合更加紧密从而进一步增大结晶度。电导特性和空间电荷特性的改善主要由于纳米TiO2形成交互区以及聚集态结构改变对陷阱特性的影响,在较低场强下测试得到的电导活化能的增大即对应为复合介质的深陷阱能级的增加,因此电荷注入得到了明显的抑制。电荷陷阱的引入也使得电导率随粒子含量的增加而减小。直流击穿场强的提高则是由聚集态结构和陷阱特性两者共同作用导致的。因此,高压直流电缆用交联聚乙烯材料可以采用添加微量纳米TiO2(0.5%)进一步改善直流介电性能,偶联剂处理过程则使得改善效果更加显著。

In order to explore the method of improving the DC dielectric properties of crosslinked polyethylene for HVDC cable, a small amount of nano-TiO2 (0.1%, 0.5%, 1%) were added into the crosslinked polyethylene matrix for DC cable using the melt blending method. The effect of surface modification on the dielectric properties of XLPE/TiO2 was studied. Moreover, the dispersion of TiO2 was observed by SEM, and the crystallinity, the conductivity at different temperatures, space charge injection characteristics and DC breakdown field strength of XLPE and XLPE/TiO2 nanocomposites were tested. The results show that surface modification can improve the TiO2 nanoparticle dispersion, the addition of nano-TiO2 to XLPE for DC cable can increase the crystallinity, conductivity activation energy and DC breakdown field strength, reduce the conductivity and suppress the injection of positive charges, and surface modification using a coupling agent can make these effects more significant. It is suggested that the nanoparticles act as nucleating agents, leading to the increase of crystallinity, and the coupling agent modification made the particles and matrix more close to further increase the crystallinity. The improvement of conductivity and space charge characteristics is mainly due to the effect of interaction area formed by nano-TiO2 and the morphology on the trap characteristics. The increase of conductivity activation energy measured at lower field strength corresponds to the increase of deep trap energy, so the charge injection is significantly inhibited. The introduction of charge traps also decreases the conductivity with the increase of particle content. The DC breakdown field strength can be increased by the morphology and the trap characteristics. Therefore, adding 0.5% nano-TiO2 into crosslinked polyethylene material for HVDC cable can further improve the DC dielectric properties, and the coupling agent modification will make the improvement more significant.