Development of Breakdown Test Setup for Liquid and Solid Insulation Materials for High Voltage Cable Accessories

Abstract

High-voltage cable accessories rely on interfaces between solid polymeric insulation and insulating liquids, also referred to as lubricants, to accommodate dimensional tolerances during installation and reduce local electric field stress. These interfaces are often the weakest point in cable joint, yet standardized breakdown test methods that account for both material types remain limited. This thesis addresses this research gap by developing and improvising experimental breakdown test setups for the solid insulation materials which is unfilled EPDM and filled EPDM (also called FGM), and liquid insulations silicone oil and silicone grease, under both AC and DC voltage. The work combines physical breakdown testing with COMSOL simulations of the electric field distribution at stress points (triple point or other stress regions) along with Weibull analysis to characterize breakdown strength of insulation materials across various electrode geometries. Moulded design was iteratively refined to reduce air cavities and control sample gap distance and a dedicated liquid test cell was developed to enable controlled and reproducible breakdown testing of high viscous lubricants. This report will give an insight into the motivation behind testing both insulation materials, the underlying physics of electric field and breakdown behaviour and the experimental setups developed over the course of the thesis. The resulting findings on how test geometry and material properties influence breakdown performance were investigated and explained in the results chapter.