Measurement and dimensional analysis modelling of electroluminescence in low density polyethylene material

Abstract

Ageing process in power cables is inevitable especially cables under prolonged application of strong electric field for many years. Ageing is normally associated with space charge accumulation at the electrodes or in the bulk of the polymeric material. Many established non-destructive methods are available in detecting the space charge distribution in the material. However, most of these methods have limited spatial resolution thus producing large uncertainty in observing the space charge profiles near the electrodes. One method that has captured a lot of attention over the years for its reliable results and data thus enhancing the knowledge in the initiation of electrical ageing of polymeric insulation is known as electroluminescene (EL) method. EL is associated with the generation of charge carriers within the polymeric material and that these charges can be produced by injection, detrapping and field-dissociation. This thesis is based on the investigation of EL emission in virgin and aged low density polyethylene (LDPE) subjected to high alternating field. LDPE is chosen as the investigated material due to its vast usage in high voltage field. The behaviour of EL emission which can be affected by several factors such as, among others, applied voltage, applied frequency, ageing of material and types of materials and gases used. In all experiments, EL emission increases with increasing applied voltage. In aged LDPE, EL emission increases with increasing ageing temperature but decreases with increasing ageing duration. However, no specific pattern can be concluded for EL emission under applied frequency. A mathematical approach relating some of these factors and the intensity of EL is proposed and developed through the aid of Dimensional Analysis method. A close relationship between the model and experimental data obtained suggests that this mathematical approach can be utilized as a tool to predict electrical ageing of insulation material.