Experimental Study and Mechanism Analysis of Composite Insulator Chalking in Extra-High Voltage (EHV) Transmission Line

Abstract

The chalking of composite insulators is referred to a kind of abnormal aging of the silicone rubber sheds. It has serious adverse effects on the long-term operation of the insulators, but the mechanism behind its generation and development remains unclear. In order to deeply understand the phenomenon of composite insulator chalking, this paper took chalked composite insulators operating on extra-high voltage (EHV) AC 500 kV as samples for research. Appearance inspection, hydrophobicity test and tensile stress test were performed on the samples to determine the change of their surface properties after chalking. It is found that a layer of white powder was formed on the surface of the sheds, the hydrophobicity level of which come to a range from HC1 to HC4, and the tensile stress tolerance and mechanical strength of the silicone rubber decreased significantly. Further, XPS analysis, FTIR detection, and TG analysis were carried out to explore the microscopic process inside the material during its chalking. The results show that the oxidation reaction of Si-C bond transforms the composition of silicone rubber, bringing damage to its apparent performance; the generation of strong polar groups such as –C=O group is the main reason for the decrease in the flexibility of the silicone rubber structure and then the formation of a powdered layer; and above all, the chalking process is based on a series of chemical decomposition reactions, in which the decomposition of polydimethylsiloxane (PDMS) as silicone rubber matrix plays a predominant role, and the decomposition of aluminum hydroxide (ATH) serves as a secondary.