Electrically-active defects in silica-filled epoxy as revealed by light emission analysis
Résumé
Epoxy resins have long been used as the insulation of electrical systems. They are generally formulated with a dispersion of micro-fillers to improve thermal and mechanical properties. However, there are concerns about the possible influence of these fillers on the electric behaviour, especially on the long term ageing under functional stresses. At the loose interface between matrix and fillers, macro- and micro-voids in the resin can provide weak points that are difficult to detect using conventional spectroscopy. Light emission analysis from the material under electrical stress is an efficient way to reveal such electrically active defects since internal ionizing events would give rise to photon emission. A detailed analysis of the light emitted by silica-filled and unfilled epoxy samples is presented. The photon counting technique, spectral analysis and imaging give a firm basis to discuss the contributing emission processes to the detected signal. They reveal the existence of ionizing events into internal defects. The sensitivity of the optical method is order of magnitudes higher than the sensitivity of conventional partial discharge detection.