THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Voltage Stabilizers: From Design to Synthesis, Processing and Electrical Characterization

Voltage stabilizers are additives capable of inhibiting electrical treeing; a degradation mechanism for insulation materials subjected to strong divergent electric fields. The intended use is in cross-linked polyethylene (XLPE) high voltage power cable insulation where minute defects in the manufacturing process can give rise to the conditions needed for the initiation of treeing, which in the worst case scenario leads to failure of the insulation system with blackouts and expensive repairs as a consequence. The main purpose of this thesis is to develop a deeper understanding of the underlying mechanisms of voltage stabilization. A robust test method for the purpose of studying electrical tree initiation was developed and used throughout this thesis. This test method is further analyzed in the thesis of Anette Johansson, twin PhD collaborator in this work. A range of voltage stabilizers were evaluated in treeing experiments. Molecular modelling was used to calculate several molecular properties and clear trends were found relating the stabilizing efficacy to the electron affinity of the voltage stabilizer. An increase of more than 100% in the average onset field of electrical treeing has been achieved using a small addition of 0.33wt% of voltage stabilizer, which is also compatible with modern cross-linking methodology.