Simultaneous measurement of Electroluminescence and dissipation current in cable insulation

Polymeric materials are widely used in high voltage devices such as capacitors, cables and transformers. Electroluminescence (EL), the emission of light in insulating materials subjected to high electric stress, is known to occur much before partial discharge inception. EL emission has been linked to the presence of space charge in the polymeric insulation. At high ac fields, charge injection from the electrodes into the insulation becomes dominant and the dissipation current becomes nonlinear. This paper describes the simultaneous measurement of EL emission and dissipation current in LDPE subjected to uniform ac field. It is shown that at the onset of EL emission the dissipation current waveform deviates from its sinusoidal characteristics and starts to show harmonics. The increase in the harmonic distortion of the dissipation current could indicate a change in the ac conduction mechanism.