Temperature dependence of epoxy resistance to PD

In this paper are presented the results of a research program on comparative test procedures on epoxy materials, in the presence of internal partial discharges under varied thermal working conditions. These studies involved only two materials. New data on other materials, filled and unfilled, are presented and analyzed. The time to breakdown of specimens subjected to 25 kV sinusoidal voltage under different testing temperatures is examined. A modified version of the CIGRE test cell, Method I, is used to obtain specimens with an hemispherical internal cavity geometry between embedded electrodes. This arrangement permits very high signal to noise ratio values and thereby fully exploits the recent digital techniques based on pulse amplitude analysis and off-line treatment of recorded data. Finally, different discharge mechanisms, governing the aging activity of cavities at 20 and 80°C respectively, were observed