Condition Assessment of Water in High viscosity Insulating Cable Termination Oil

Abstract

Oil-filled terminations for high voltage XLPE insulated cables have been used for four decades in the Netherlands with a good service record. Prysmian would like to gain better insight into the effects of water contamination in insulating oil, to further extend the in-house experience and potential related failure mechanisms. High voltage termination is contained within a bushing that is filled with insulating cable oil. The insulating cable oil is a containment medium for the electric field lines and should have low dielectric losses, chemical inertness against the construction material, non-flammability and stable electrical property during prolong heating. The insulating oil is also self-healing, leaving no permanent conductive path in the fluid. The containment should be well-sealed to prevent any forms of leakage from the surroundings. The initial stages of the thesis seeks to inventory and address a few topics, mainly regarding water polluting oil. Studies will be done into the phenomena surrounding water within oil, the influence of water particles on the electrical performance of the oil, movement of water within the termination during temperature gradients and movement of water within the termination during electrical gradients. The next step is to inventory the current on-line and off-line tools available for measurements of water contents in oil. They would be AC voltage breakdown test, dielectric loss measurement, partial discharge detection, permittivity measurement and humidity check. Finally, the last phase would look to find mitigation techniques integrating the given inventories and observations, so as to formulate non-intrusive diagnostic methods to ascertain polluted terminations.