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

A dynamic bipolar charge recombination model is proposed to explain the charge injection and electroluminescent behaviour found experimentally 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 electroluminescence intensity at constant alternating stressing voltage is accounted for by charge trapping in the polymer close to the electrode and recombination via mobile charge recombining with trapped charge of opposite polarity. The phase profile of the electroluminescence is a consequence of charge injection across a potential barrier and field limiting behaviour occurring at the injection electrode. The saturation electric field under field limiting conditions and the injected current density as a function of time can be calculated from the experimental conditions and knowledge of the charge injection law. Field limiting behaviour provides a feedback mechanism that maintains net charge neutrality within the resin over time.