Abstract
Recently, it is reported that vented water trees have likely been initiated due to contaminants causing degradation structures within the bulk of the semiconductive (SC) screen, rather than at the interface with the insulation. The aim of this study is to reproduce the degradation phenomenon, observed as voids and nanostructured paths, to better understand its origin and mechanisms. Using a combination of disc-shaped samples, Rogowski test objects, and aged cables, the research explores how impurities and thermal -and electrical ageing influence the degradation. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is used to assess Na+ diffusion, while breakdown strength testing and water tree analysis quantifies the impact of ageing on dielectric performance. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) are used at degradation sites, and Thermomechanical Analysis (TMA) evaluates the residual stress and thermal behaviour. Results show that contaminants like NaCl can be a contributing factor to the degradation phenomenon connected to water tree initiation. The findings highlight the complex interplay of chemical, thermal, and electrical factors in the insulation system degradation and underscore the need for refined analytical methods and integrated testing to better predict long-term cable performance.