178 / 2018-08-25 23:09:22

Study on Water Tree Aging Characteristics of Crosslinked Polyethylene Silica Nanocomposites

crosslinked polyethylene,nano-SiO2,water tree,crystal morphology,fracture energy

Water tree would be initiated and growth easily when crosslinked polyethylene（XLPE） insulated cable is operated under high electric field and humid environment, leading to the formation of electrical trees or even to insulation breakdown, which seriously endangers security of power grid. Therefore, it is of great significance to research water tree resistant XLPE materials with excellent dielectric performance, which will improve the quality of cables and enhance the reliability of power grid. In this paper, XLPE/SiO2 nanocomposite was prepared by melting blending method, the effects of the doping amount of organic nano-SiO2 on mechanical properties, morphology and behavior of water trees were studied. The results show that the doped nano-SiO2 particles into XLPE form a strong chemical bond linking with the matraix by saline coupling agent, acting as physical crosslinking points. On the one hand, the organic SiO2 can evenly distribute the load, and timely transfer the stress to other molecular chains in time to disperse the stress. On the other hand, it enhances the intermolecular forces of XLPE and improves the toughness of the composites, therefore the ductile growth of microcracks can be inhibited by absorbing the fracture energy. Moreover, as the nucleating agent, nano-SiO2 particles play a role in heterogeneous nucleation in XLPE, which increased the crystal quantity and decreased the grain size, making the grain distributing more regular. The amorphous area is reduced. The diffusion resistance of water molecules is increased, and the penetration ability is weakened, thereby the growth of water trees are hindered and delayed.
The nanocomposite was conducted accelerated water tree ageing tests and the morphology of water tree was observed by polarizing microscope, the growth probability and length of water trees was also counted. The results experimental shown us that it has a positive influence on the resistance to water tree of the nanocomposite material which doped modified by silica. The growth probability of water trees has decreased and length of water trees on the crosslinked polyethylene/silica nanocomposite is become shorter as long as the increase of silica content. Compared with the pure crosslinked polyethylene, it has a best effect on the inhibition of water tree when the content of silica was 3%. At the same time, the length of water tree along the direction of the electric field is 260μm and decreased 54.1%. The length of water tree vertical the direction of the electric field is 481μm and decreased 48.7%. Meanwhile, the water trees growth probability fells to 10%.

Key words- Crosslinked polyethylene;Nano-SiO2;water tree;Fracture energy; Crystal morphology