Metallographic investigation of the damage caused to GRP by the combined action of electrical, mechanical and chemical environments

Abstract

The use of glass fibre-reinforced polymers in electrical insulator components has gradually been taking place. Problems may arise where such insulators are in service at very high voltage, e.g. 200 kV and above, are under significant mechanical loads, and the environment (rain, and various pollutants) is able to gain access to the surface of the GRP. With the aid of optical and scanning electron microscope techniques, a detailed examination has been carried out on the nature of damage which has taken place in GRP pultruded rods that have operated for various periods of time in the above service conditions. These pultruded rods can receive significant levels of damage under the action of electrical fields, and the attendant environment; this takes the form of erosion, melting, burning and displacement of both glass and polymer phases. When a mechanical stress, which may be less than 10% of the breaking stress of the rod, is applied in conjunction with the above conditions a different form of insulator breakdown can take place. Instead of material displacement on the scale mentioned above, brittle failure of the GRP takes place. Such a failure mode can be compared with the process of stress corrosion which takes place when GRP is tested in 0.1 N acid solutions. It is suggested that the combined action of electrical activity and the presence of minor amounts of pollutants are able to influence the surface of glass fibres and promote stress corrosion in an analogous fashion to that described for concentrated acid solutions.