Influence of montmorillonite on electrical treeing and breakdown characteristics of low-density polyethylene

Abstract

Electrical treeing is an electrical aging phenomenon that severely threatens the operation safety of power equipment, in which polymer is used as primary insulation material. A type of low-density polyethylene-montmorillonite (LDPE/MMT) nanocomposite was prepared using melt method to study the impact of MMT nanoparticles on the growth of the electrical tree and on the breakdown properties of the LDPE material. The distribution characteristic of space charges of the specimens under DC voltage of –50 kV/mm and short-circuit conditions was measured using pulsed electro-acoustic method. The electrical tree aging characteristics of specimens under AC voltage of power frequency were studied using needle-plate electrode structure test platform. The starting voltage of initiation, the triggering rate, and the growth rate of the electrical trees, as well as the breakdown performance of the specimens under AC voltage of power frequency were measured. The inhibitory mechanism of MMT nano-particles on the growth of electrical trees in nano-composites, and the mechanism behind the improvement of the breakdown strength of the LDPE/MMT specimens were illustrated. Experimental results showed that, the addition of MMT can effectively reduce the amount of space charges injected from electrodes and the accumulation amount in the center of samples. Moreover, space charges dissipated more slowly during short-circuit conditions. The speed and the scale of the growth of the electrical tree declined as the initiation conditions of electrical trees growing in LDPE/MMT nanocomposites increased; meanwhile, the breakdown strength increased substantially. Here are the reasons: MMT can reduce the mobility of carriers in LDPE material, thereby contributing to the improvement of the distribution of space charges. In the meanwhile, MMT changed the development path of electrical trees, and extended the discharge distance. Consequently, MMT postponed the occurrence of penetrable breakdown in the LDPE/MMT specimen, and ultimately improved the breakdown strength of the specimen.