Research in field distortion by cavity presence in HVDC cable and the associated partial discharge characteristics
This thesis explores the electric field enhancement by a single cavity presence inside a high voltage direct current cable and the associated partial discharge characteristics at the steady state. Electrical conductivity is indicated to be important in determining the field enhancement inside the cavity and the field distortion in the region surrounding the cavity. The volume of the region possibly influenced by the cavity is given, and it is never higher than five times the cavity radius for a single spherical cavity. The conclusions are applicable across the range of cavity locations, cavity sizes, temperature differences, and material properties studied in the project. At the present stage, no numerical model on partial discharge at direct current voltage is published. In this project, preliminary modelling and simulation work is researched based on Niemeyer's model, which is an accepted model at alternating current voltage, with modification according to its physical mechanism. Electrical conductivity of the insulation bulk is important in determining the characteristics of partial discharge, including the discharge repetition rate and discharge magnitude. The conclusion is applicable across the current through the conductor, cavity location and fresh and aged material studied in the project.