Dynamic bipolar charge recombination model for electroluminescence in polymer based insulation during electrical tree initiation

Abstract

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.

Characteristics of electroluminescence phenomenon in virgin and thermally aged LDPE

“…It can be observed that EL emission intensity for virgin sample increases as applied voltage increases. By increasing the voltage applied, the charge injection increases and thus increases the chances of charge recombination processes [4]. It can also be seen that EL intensity is much larger at positive half cycle than that of negative half cycle for all applied voltage.…”

Investigations of electrical trees in the inner layer of XLPE cable insulation using computer-aided image recording monitoring

“…Based on proposed initiation and propagation mechanisms of electrical trees [10,[16][17][18][19][20][21][22] and the experimental results in this paper, it is suggested that similar initiation mechanisms exist among all of the trees in our experiments [14,15,23]. The initiating processes of electrical tree in the inner layer of 66 kV XLPE cable are: electron injection and extraction at the needle electrode due to high electric field, part of the insulation in the front of needle will be deteriorated by this process, this is followed by the intense partial discharge and photo-ionization due to charge recombination in the channel of the tree, the continuous micro-breakdown at the tree tips and the electron avalanche mechanisms, etc.…”

Analysis of electrical tree inception in silicone gels

“…This restriction was lifted in [29] where injection currents from a divergent field electrode were calculated for sinusoidal applied voltages when space charge was accumulated in the polymer. Recombination between mobile charges from the injection currents and trapped charges of opposite polarity from the previous half-cycle were shown to be able to reproduce the behavior of electroluminescence during the first stage of tree inception in epoxy resin [29]. This work gives a means of calculating the injection currents, the space charge, and the electric field, around an injecting electrode in either a sinusoidal or repeated square wave applied voltage.…”

“…The details of this model are given in [29]. Its main physical features are that during an increasing applied voltage the injection current increases with electrode field until the space charge it produces is big enough to limit the field to a constant value.…”

“…In [29] equation (6) was adopted because it fits to the regime of fields and temperatures commonly occurring for which neither the Schottky-Richardson (low field -room temperature) nor the Fowler-Nordheim, (high field -low temperature) approximations apply [30,31]. This equation introduces two constants α and β, which depend on the temperature and potential barrier height.…”