English Abstract
Hydrophobicity and Multiple Aging Phenomena of Polymer Insulators.
Noboru Yoshimura,
Department of Electrical and Electronic Engineering, Akita University, Akita,Japan.
Seiji Kumagai,
Department of Machine Intelligence and Systems Engineering, Akita Prefectural University, Akita,Japan.
Nippon Gomu Kyokaishi,(2003),76(4), 119-124 General Review in Japanese.

Advantages of polymer insulators over traditional ceramics insulators are light weight, high mechanical strength to weight ratio and high vandal damage resistance. Easy handling, easy installation and the thereby reduced cost are expected to contribute to more effective and labor-saving power delivery systems. The induced aging can reduce the electrical performances as well as the durability of polymer insulators. This is a peculiar nature of polymer insulators.

Nowadays, silicone rubbers incorporated with alumina trihydratefiller are
representative housing materials of polymer insulators. One merit of using silicone rubbers is providing stable hydrophobicity, which can be quickly recovered even when it is lost as a result of discharges and/or deposits of contaminations, to insulator surfaces. Stable and recoverable hydrophobicity prevents water film to form, restricting leakage current passing through the water film and thus enhancing the capability of electrical insulators even in wet and contaminated conditions. Fundamental understanding is reviewed on the loss and the recovery of hydrophobicity of silicone rubbers in association with a formation of low molar mass cyclic silicone oligomers, a formation of silanol groups and an orientation of methyl groups. A correlation of the hydrophobic variation with the electrical insulating performances is also reviewed.

polymer insulator, silicone rubber, hydrophobicity, contamination, leakage current