Search

A cable sealing end is a crucial power system component as it is responsible for the vital task of successfully terminating cables. Recent reports on the diagnosis of ex-service units have led us to investigate possible contaminations that could impact the dielectric properties of a cable sealing end. Verdigris, often blue/green in color, is one such contaminant that is observed on the surface of a cable stalk. This investigation aims to understand the possible cause of this contamination and its impact on the dielectric liquid used inside a polymeric cable sealing end. To achieve this, the current study is devised in two parts. First, a sample of the verdigris is scraped off from the cable stalk surface and analyzed. The elemental composition of the blue verdigris is analyzed using energy-dispersive X-ray methods on a scanning electron microscope. Second, sonication ageing tests are performed on samples of silicone oil that have been contaminated with verdigris. Elemental analysis shows traces of carbon, oxygen, sodium, silicon, tin and copper contaminations as the primary components of the verdigris present in different percentage. The results from the second half of the study obtained shows an increment in dielectric permittivity and moisture measurements, whereas not much change was reflected in the UV-vis analysis when compared with fresh oil sample.

The UK is facing two major challenges in the development of its electricitynetwork. First, two thirds of the existing power stations are expected to close by2030. Second, is the requirement to reduce its CO2 emissions by 80% by 2050.Both of these challenges are significant in their own right. The fact that they areoccurring at the same time, generates a significant amount of threats to theexisting power system, but also provides many new opportunities.In order to meet both these challenges, significant amounts of offshore windgeneration has been installed in the UK. For the wind generation with thelongest connections to land, Voltage Source Converter (VSC) based HighVoltage Direct Current (HVDC) transmission has to be used.Due to the high power rating of the offshore wind farms, compared to the limitedtransmission capacity of the links, a large number of point-to-point connectionsare required. This has lead to the concept of HVDC grids being proposed, inorder to reduce the amount of installed assets required.HVDC grids are a new transmission environment and the fundamental questionof how they will protect themselves must be answered. Several newtechnologies are under consideration to provide this protection, one of which isthe HVDC circuit breaker.As HVDC circuit breakers are a new technology, they must be tested in alaboratory environment to prove their operation and improve their TechnologyReadiness Level (TRL). This thesis is concerned with how such HVDC circuitbreakers are operated, rated, and tested in a laboratory environment.A review of the existing circuit breaker technologies is given, along withdescriptions of several novel circuit breakers developed in this thesis. Astandardized method of rating DC circuit breaker and their associated testcircuit is developed.Mathematical analysis of several circuit breakers is derived from first principlesand low power prototypes are developed to validate these design concepts. Ahigh power test circuit is then constructed and a semiconductor circuit