DYNAMIC BIPOLAR CHARGE RECOMBINATION MODEL FOR ELECTROLUMINESCENCE INPOLYMER-BASED INSULATION DURING ELECTRICAL TREE INITIATION

A dynamic bipolar charge recombination model is proposed to explain th e charge injection and electroluminescent behaviour found experimental ly in pin-plane polymeric resin samples under high alternating voltage stress. The model is described for two electrode geometries producing parallel and divergent electric fields. The long term rise in electro luminescence intensity at constant alternating stressing voltage is ac counted for by charge trapping in the polymer close to the electrode a nd recombination via mobile charge recombining with trapped charge of opposite polarity. The phase profile of the electroluminescence is a c onsequence of charge injection across a potential barrier and field li miting behaviour occurring at the injection electrode. The saturation electric field under field limiting conditions and the injected curren t density as a function of time can be calculated from the experimenta l conditions and knowledge of the charge injection law. Field limiting behaviour provides a feedback mechanism that maintains net charge neu trality within the resin over time.