Electric Field Induced Orientation Of Montmorillonite In Polyethylene And Properties Of Electrical Tree Growing In This Composite

Polyethylene (PE) is a type of solid polymers with excellent dielectric and heat resistantproperties, which has been commonly used as insulating material for power cables. Electrical tree has been recognized as one of the important reasons to cause insulation damage in polymer cables, especially the electrical tree growth in PE which could lead to the electric breakdown of power cables, and which is a serious threat to the safety operation of the power system. Some researchers already presented that Low-density polyethyene/montmorillonite (LDPE/MMT) composites prepared by melting intercalation process has better electrical tree suppression properties. The reason is mainly that electrical tree would encounter the MMT sheet in its developing process. This will change the developing track and make the electrical tree grow along the MMT surface. In this way, the extension of the discharge distance would be extended, and the throughout breakdown caused by electrical tree growth would be also delayed. In recent years, many researchers prepared a lot of anisotropic materials using electric field induced and found that their optical properties, mechanical properties and electricity performance improved significantly. Assuming a new LDPE/MMT composite, in which the MMT sheets are in one direction perpendicular to the electrical tree growth. The growing electrical tree would encounter the MMT sheet, which would change the growth way to the original growth direction. Thus the discharge path would be extended to maximum level and the electrical tree would be inhibited effectively.In this paper, a new strategy that orientated MMT in the LDPE matrix by electric field was described, and which could improve the electrical tree properties. A new orientation setup was designed and manufactured. According to the orientation principle, the right temperature and electric field strength were calculated. The base performances and electrical tree properties of LDPE/MMT with different MMT content before and after being electric field induced were investigated. The main findings are as following:①With theoretical calculations and exploratory experiment, the induction temprature was170℃and the induction electric field was industrial frrequency ac electric field of18kV/mm.②The resutls of UV light transmission rate, X-ray diffraction curve and SEM figure demonstrated that the orientation of MMT occur after being electric field induce. The thermal properties of LDPE/orientated MMT did not change, but its dielectric strength appeared anisotropy.③The optiaml content of MMT for LDPE/MMT nanocomposite is1%. In this case, MMT has the best dispersion, good compatibility with LDPE, and has the best blocking ability to the growth of electrical tree. When MMT content was5%, MMT was bad dispersion, which could cause properties deterioration.④For LDPE/orientated MMT composite, its electrical tree starting voltages could be increased, the speed and scale of electrical tree growth could be reduced. Partial discharge results explained the reason for above phenomenon was that MMT with good dispersion weakened partial discharge. At the same time, the orientated MMT could extend the discharge distance and enhance the barrier of water and air. As a result, the suppression capacity for electrical tree of LDPE/orientated MMT composite enhanced markedly.