Suppression of electrical discharges

SF6 (Sulphur HexaFluoride) gas is exclusively used as a dielectric insulator and arc quenching medium in high voltage power networks. The electronegative properties of the gas and its ability to recombine after dissociation make it a gas of choice for high voltage equipment. However, SF 6 is a greenhouse gas and therefore research is needed to find an alternative. This thesis explores the potential of PolyTetraFluoroEthylene (PTFE) powder as a dielectric insulator. This has been deployed in a compacted form and when buoyant in air. This approach opens up new avenues for existing research related to gaseous dielectrics and current interruption through the utilisation of small particulates made from insulating materials. A detailed database, of breakdown voltage signals and high speed camera shots, has been compiled to facilitate comparative analysis of the effect of airborne polymer (e.g. PTFE) powders on breakdown voltage across different gap widths, relative to SF6. The breakdown voltage results which were obtained from experimental tests to demonstrate an effect on the voltage withstand that these airborne materials have comparable to that of SF6. Also, their ability to suppress electrical discharges between dielectric probe contacts is also demonstrated during the course of this thesis. In addition, a combined electrical/optical system has been constructed in order to investigate the relationship between airborne particle concentration and the resultant breakdown voltage between electrodes. The optical system was tested using smoke particles prior to its utilisation for powder particles. For both smoke and powder systems, chromaticity was utilised to assess changes in particle density. A model was used to interpret the optical signal and thereby estimate the concentration of airborne particles. This employs factors such as the refractive index, particle radius and essentially the ratio of the light source intensity as seen through the container with scattering particles to the intensity of the same light source seen through the same container without scattering particles.EThOS - Electronic Theses Online ServiceGBUnited Kingdo