Effects of SiC nanoparticles on space charge behaviors of LSR/nano-SiO2/nano-SiC composites for insulating material of HVDC cable joints

Abstract

In order to develop insulating materials for high-voltage direct current (HVDC) cable joints, silicone nanocomposites are prepared by mixing liquid silicone resin (LSR) with the surface-modified nano-SiO2 and the surface-modified SiC nanoparticles, and the effects of SiC nanoparticles on space charge behaviors of the silicone nanocomposites are studied. The hydrophilic surface of the fumed nano-SiO2 is modified into a hydrophobic surface by treating with an alkyl silane coupling agent in order to be uniformly dispersed in LSR, and the surface of the SiC nanoparticles is modified with a vinyl silane coupling agent in order to improve the interfacial characteristics through covalent bonds between SiC nanoparticles and LSR. LSR is mixed with the modified nano-SiO2 (20 wt%) and the modified SiC nanoparticle (0 wt%-9 wt%). To observe the even dispersion of the modified nano-particles in LSR matrixes, a transmission electron microscope is employed and it is found that nano-SiO2 and nano-SiC particles are somewhat uniformly dispersed regardless of their content. When an appropriate amount of semiconductive nano-SiC particles is uniformly dispersed in the LSR/SiO2 nanocomposite, space charges are evenly dispersed. Therefore, the HVDC breakdown strength of the LSR nanocomposite would increase. However, if nano-SiC is mixed in excess, the conduction paths are formed, therefore the HVDC breakdown strength would decrease. HVDC breakdown strength under positive polarity condition shows the maximum value, 99.8 kV/2 mm in the nanocomposite with 3 wt% nano-SiC, which means that the space charge distribution is optimal in the 3 wt% nano-SiC system. However, excessive nano-SiC adversely affects the HVDC breakdown strength.