Study of treeing in epoxy-alumina nanocomposites using electroluminescence

Dielectric materials in electrical equipment are mostly subjected to non-uniform or divergent field conditions. Localized high electric field may give rise to space charge which may initiate material degradation, and eventually lead to dielectric breakdown. Thus, it is important to assess the performance of nanocomposites under divergent fields before deployment as insulation. Past research has shown a positive correlation between space charge and electroluminescence (EL). In this work, EL is used as a diagnostic tool to study space charge and field-related material degradation in epoxy-alumina nanocomposites. Various experiments are undertaken to detect early stages of material degradation through EL. These include endurance tests (below and above EL emission threshold), and characterization of EL from samples pre-stressed with DC and/or AC voltages. The effect of repeated square waves on material degradation is also analyzed. Visual inspection for physical damage is carried out using a high resolution camera. The EL signature is observed to deviate significantly from its initial value at the onset of material degradation, and may therefore serve as an aging marker. In addition, the EL studies show that nanocomposites exhibit a relatively high resistance to field-assisted material degradation. The experiments on pre-stressed samples indicate that charge kinetics play a crucial role in defect initiation and material degradation.