Electrical Tree Characteristics of Isotactic/Syndiotactic Polypropylene Blend Insulation under Repetitive Impulse Voltage

摘要

Polypropylene (PP) is an emerging direction of thermoplastic and crosslink-free cable insulation material due to its excellent electrical and heat resistance properties. This article concentrates on the electrical tree characteristics of Isotactic PP (iPP)/Syndiotactic PP (sPP) blend insulation under repetitive impulse voltage. Five samples of iPP/sPP blend with sPP contents of 0, 5, 15, 30 and 45 wt% were prepared in aim to analyze the electrical tree initiation and growth characteristics. Electrical tree tests under repetitive impulse voltage were performed by the needle-plate electrode system under 30, 50, 70 and 90°C. When sPP content is between 0 and 15 wt%, the increase of sPP content inhibits the growth of electrical tree. With the continuing increase of sPP content, the initial probability and growth rate of electrical tree rise due to the decrease of deep trap density. The PP blend with 15 wt% sPP shows an excellent resistance to electrical tree, which is attributed to the highest deep trap density. Deep traps are easier to capture injected charges and form homogenous electrical field, which results in the inhibition of charge injection under repetitive impulse voltage. Moreover, the increased deep trap density is conducive to reduce the mean free path of charges and confine impact ionization, resulting in the lower growth speed of electrical tree.