This paper examines the data collected from the power industry over the last six years of actual reported emissions of sulphur hexafluoride (SF₆) and the potential impact. The SF₆ emissions have been collated from the 14 different regions in England, Scotland, and Wales (Great Britain) from the six distribution network operators. The emissions of SF₆ due to the transmission network of Great Britain have also been collated from the three different transmission network operators. By collecting this SF₆ emissions data from the power industry, in both the distribution and transmission networks, an overall view of the scale of SF₆ emissions in Great Britain can be evaluated. Data from the power industry also shows the inventory of SF₆ power equipment in use over the last six years in Great Britain and shows the calculated percentage leakage rate of all of this equipment. In this paper, these figures, as reported by the electrical power industry to the UK government, have been used to estimate the likely inventory of SF₆ equipment in England, Scotland, and Wales by 2050 and the future emissions of SF₆ that could be leaked into the atmosphere by this equipment.

In this paper, sulphur hexafluoride (SF₆) insulated vacuum interrupter circuit breakers have been used to explore replacing SF₆ gas with a trifluoroiodomethane and carbon dioxide (CF₃I-CO₂) gas mixture. The search for an alternative insulation gas is driven by the well known extreme global warming potential of SF₆. For this purpose, the circuit breaker gas compartment of a piece of gas insulated switchgear (GIS) was filled with a CF₃I gas mixture and then tested using lightning impulses up to the rated withstand strength. The tested ring main unit was initially designed to be insulated with SF₆ gas. The unit is a three-phase switchgear containing two switches per phase; a selector interlock and a vacuum bottle circuit breaker per phase. The test programme performed in this investigation demonstrated the breakdown performance and insulation strength of the new gas mixture as well as the vacuum circuit breakers behavior when insulated with a new insulation medium. Data on the dielectric properties of the proposed gas mixture is presented, and the performance of the tested vacuum circuit breaker is discussed. Promising results are obtained which indicate the suitability of this more-environmentally friendly gas for high voltage insulation purposes.

Creeping discharges over insulator surfaces have been related to the presence of triple junctions in compressed gas insulated systems. The performance of dielectric materials frequently utilised in gaseous insulating high voltage applications, stressed under triple junction conditions, has been an interesting topic approached through many different physical perspectives. Presented research outcomes have contributed to the understanding of the mechanisms behind the related phenomena, macroscopically and microscopically. This paper deals with the electrical detection of creeping discharges over disc-shaped insulator samples of different dielectric materials (polytetrafluoroethylene (PTFE), epoxy resin and silicone rubber) using atmospheric gases (dry air, N₂ and CO₂) as insulation medium in a point-plane electrode arrangement and under AC voltage application. The entire approach implementation is described in detail, from the initial numerical field simulations of the electrode configuration to the sensing and recording devices specifications and applications. The obtained results demonstrate the dependence of the generated discharge activity on the geometrical and material properties of the dielectric and the solid/atmospheric gas interface. The current work will be further extended as part of a future extensive research programme.

This paper evaluates the insulation performance of gas mixtures of trifluoroiodomethane and carbon dioxide (CF₃I-CO₂) in a medium voltage switch disconnector. Practical testing compares the results of CF₃I-CO₂ against SF₆ to examine whether CF₃I-CO₂ could be a viable alternative when directly substituted into manufactured switch disconnectors in a purely insulating role. Positive standard lightning impulses were applied to the MV switchgear to determine whether CF₃I-CO₂ can maintain the withstand voltage for which the switch disconnector is rated when filled with SF₆. The results show that certain gas mixtures of CF₃I-CO₂, with a higher concentration of CF₃I, could be used to insulate switch disconnectors against standard lightning impulses at the rated pressure.

This paper investigates the solid by-products of CF 3 I-CO 2 gas mixtures and their proposed use as an alternative insulation medium in gas insulated switchgear and lines. The deposited by-products of a 30%-70% CF 3 I-CO 2 gas mixture are experimentally investigated using stainless steel, aluminium and copper contacts whilst a standard 50 kV lightning impulse is used to cause electrical breakdown in the gas mixture. Following breakdown, the accumulated by-products over the electrodes surface were examined using an imaging microscope and scanning electron microscope. This paper discusses the results of microscope analysis on the surface of the electrodes and explores the effects that the detected by-products could have on high voltage CF 3 I-CO 2 gas insulated equipment.

SF₆ is a widely used gas medium in gas-insulated equipment. Due to the high global warming potential and long atmospheric lifetime of SF₆, there has been research into a new environmentally friendly replacement gas. This paper describes the research carried out at Cardiff University on CF₃I gas and its mixture as a substitute insulation medium for SF₆ in gas-insulated lines (GIL). A reduced-scale coaxial test system having the electric field properties of a full-scale 400 kV GIL system was fabricated. The design of the reduced-scale coaxial test system was simulated to ensure that the highest electric field would be along the center of the conductor. The coaxial prototype was then tested under a standard lightning impulse (1.2/50) in order to determine the 50% breakdown voltage for such a system when insulated with CF₃I gas mixture. It was found that CF₃I has the potential to replace SF₆ as an insulation medium in GIL. A full-scale short length GIL demonstrator is being assembled in the laboratory to evaluate further the feasibility of using a CF₃I gas mixture as an insulation medium.