On a model for the comparative analysis of the ageing characteristics of epoxy resins subjected to internal discharges at various environmental temperatures

Different epoxy systems typically used in HV gas-insulated systems were investigated to obtain a more global view of the materials´ performance. An accurate scanning microscope analysis was carried out on the aged wall cavity and inside the breakdown channel to obtain information on which to base a model of material performance under high temperature. The time to spontaneous breakdown of samples of identical specimens having a calibrated enclosed void was used as the life criterion. Particular attention was focused on the scatter of the lifetimes. In many cases PD (partial discharge) amplitude distributions were detected during life tests by means of a computerized system, and emphasis was given to their time changes in relation to the testing temperature. This technique made it possible to obtain a more global view of material performance against PD activity for measurements carried out by means of a laboratory test cell. On the basis of the experimental results, a model that provides a deeper insight into resistance to PD, especially when comparative information between different materials is required at temperatures different from the ambient, is proposed