Review and Design of DC Electrical Field Measurement Systems and Related Developments : For Measurements Around HVDC Cable Terminations

Abstract: With power generation and consumption placed further away from each other, with for example increased offshore power production, the need for HVDC transmission systems increases. As voltage levels in the HVDC transmission system are raised, the losses can be decreased, enabling efficient power transfer over longer distances. Such an increase in voltage levels comes with questions regarding insulation performance due to increased electrical field stress in high voltage apparatus, particularly in and around cable terminations. Thus, physical measurements of electrical fields or voltage potentials in air are of interest to improve the understanding of the electrical fields around cable terminations as well as to verify and develop simulation models for use at ultra high voltage. In this thesis, different measurement systems and sensors for electrical field measurements are investigated, and their benefits and drawbacks are compared to a known previously implemented reference measurement system with known strengths and limitations. Two new conceptual measurement systems with a sensor concept and positioning system are developed and proposed for a set of given conditions, such as measurement around cable terminations in air. The first proposed system is based on a shutter field mill sensor placed on variable electric potential. The second system is based on the reference system's sensor design modified to remove the need for a large positioning system. The feasibility of the two measurement systems is investigated further utilizing a COMSOL model and a mechanical prototype. The simulation model is used for electrical field simulations around cable terminations in a 2D-axisymmetric geometry as well as a 3D geometry to verify the first measurement system. The mechanical prototype is utilized to test and verify the possibility of implementing the second system's positioning system. The two final proposed measurement systems can be further developed and used as a foundation for a future implemented measurement system.