Pattern analysis on dielectric breakdown characteristics of biodegradable polyethylene film under nonuniform electric field

This article presents pattern analysis to identify the dielectric breakdown characteristics of biodegradable polyethylene film under nonuniform electric field affected by the contaminated conditions, with low-density polyethylene (LDPE) film as the reference. When the specimens were immersed in the electrolyte for different periods, their degradation was observed and the breakdown experiments were carried out by the needle-plane electrode pattern with the air gap of 10 mm. The breakdown voltage was measured to determine the discharge and breakdown mechanism in the air/film gap under the nonuniform electric field. Meanwhile, the breakdown phenomena were captured by a monocular-video-zoom microscope, and the related breakdown characteristics were quantitatively analyzed through the methods of image processing and fractal dimension to establish the relationship between the pattern characteristics of breakdown craters and the dielectric properties. It is found that the morphology of breakdown region and the distribution of discharge profile in relationship with the contaminated levels can provide an optical evaluation method for the insulating materials. Compared with LDPE, biodegradable polyethylene shows the better breakdown endurance. By increasing the electrolyte conductivity and the immersion time, the breakdown voltage, the breakdown area, and the box dimension of the breakdown crater decrease. The breakdown voltage is higher than that of LDPE, whereas the breakdown area and the box dimension are lower. The results obtained indicate that the image-pattern identification technique is fairly well to quantify the breakdown phenomena of polymer films. Both breakdown area and box dimension reasonably give a scale to identify the dielectric properties for further investigation on feasibility of using biodegradable polymers. Copyright (c) 2011 John Wiley & Sons, Ltd.