Investigation on deterioration of Composite insulator bushing exposed to HVDC for long duration

摘要

A huge number of composite insulators have already been installed from low voltage to ultra high voltage due to their superior features, such as good hydrophobicity, simple construction, explosion proof, light weight, mechanical strength against internal pressure and bending force, seismic resistance, easy handling and cost advantage. Surveys by CIGRE have assisted to resolve the concerns about their long term reliability. Although the high insulation performance of composite insulators with HTV type sheds in various environments owing to their hydrophobicity has often been reported including heavily polluted area[1], under the condition with applying DC voltage outdoor[2], the reliability of them under applying HVDC indoor condition where there is no rinsing effect by rain has rarely been reported. The composite bushings designed for 300 kV class installed inside of the factory on which 449 kV DC voltage have been applied for over 1500 hours in total within 15 years have been investigated. The contamination on the sheds was found to be 0.177 mg/cm~2 for ESDD and 1.27 mg/cm~2 for NSDD. These levels are higher than those observed on the composite bushings exposed to heavily polluted outdoor area in Japan. The hydrophobicity on the sheds are found to be deteriorated on some sampled positions but to maintain on HC-2 to HC-3 level evaluated based on STRI method on the most of the measured positions. Leakage current under applying 250 kV DC was as small as 1 μA, which can be concluded that the bushings maintain good dielectric strength. Also hydrophobicity recovers from HC-5 to HC-2 level one week after wiping contaminated content from the sheds surface.