Evaluation of SF6 leakage from gas insulated equipment on electricity networks in Great Britain

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

Solid by-products of a CF3I-CO2 insulating gas mixtures on electrodes after lightning impulse breakdown

This paper investigates the solid by-products of CF3I–CO2 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% CF3I–CO2 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 CF3I–CO2 gas insulated equipment

Insulation strength of CF3I-CO2 gas mixtures as an alternative to SF6 in MV switch disconnectors

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

Schlieren images of negative streamer and leader formations in CO2 and a CF3I-CO2 electronegative gas mixture

In electrical networks, SF6 gas is currently used to insulate high-voltage equipment, however, due to its high environmental impact, new alternatives such as CO2 and electronegative gas mixtures such as CF3I-CO2 are being trialled to replace SF6 and create a sustainable energy system. A high-voltage lightning impulse (1.2 μs/50 μs) was used to approximate the disturbance in a high-voltage electrical network caused by a lightning strike and helped to identify the likely streamer and leader formations in different gases insulating a piece of gas insulated switchgear. In this paper, the theoretical and practical aspects of electrical streamer and leader formations in pure CO2 and an electronegative gas mixture of CF3I-CO2 are examined using schlieren videography in small length rod-plane gas gaps between 20 and 50 mm in length. Schlieren allows the examination of gas density in streamer formations and for the differences in weakly attaching gases, such as CO2, and electronegative gas mixtures, such as CF3I-CO2, to be studied. The gas pressure is varied in order to examine the differences in streamer and leader formation as the gas density is varied and hence the probability of electron collision is varied

Investigation into CF3I-CO2 gas mixtures for insulation of gas-insulated distribution equipment

This thesis reviews the use of sulphur hexafluoride (SF6) as an insulating medium in the electrical power industry and quantifies the potential global warming effects associated with its continued use. A mixture of Trifluoroiodomethane (CF3I) and carbon dioxide (CO2) is suggested as a potential alternative to SF6, and its insulation properties are examined. Pressure mixture ratios of 10%:90%, 20%:80% and 30%:70% CF3I-CO2 are used in the laboratory test programme. A test rig has been developed to safely fill and recover gas mixtures of CF3I-CO2 in switchgear. Practical medium voltage (MV) switch disconnectors and ring main units are used to test the insulation properties of CF3I-CO2 gas mixtures and compared with SF6 using standard lightning impulses (1.2/50 μs). The experimental mixture ratios are used to identify how the insulation strength varies depending on the content of CF3I used. The switchgear is filled to its normal and minimum operating pressure to observe the reduction in insulation performance of the gas mixtures when the pressure is reduced. The insulation strength is measured using the 50% breakdown voltages (U50) and withstand strengths of each gas mixture in accordance with international standards. The effective ionisation coefficients of various CF3I-CO2 gas mixtures are calculated. This process identified the estimated critical reduced electric field strengths of several CF3I-CO2 gas mixtures. Furthermore, electric field simulations utilised the effective ionisation coefficient functions and the contact geometry of a switch disconnector to predict the likelihood of a flashover occurring for various CF3I-CO2 gas mixtures. This investigation shows that CF3I-CO2 can successfully be used to insulate practical MV switchgear but is dependent on equipment design and operating pressure. It has previously been indicated that by-products of CF3I make it unsuitable to interrupt high current. Therefore, it is suggested in this study that CF3I-CO2 gas mixtures can be adopted to insulate equipment such as vacuum circuit breakers

A comparison of partial discharge sensors for natural gas insulated high voltage equipment

The research in this paper consists of practical experimentation on a gas insulated section of high voltage equipment filled with carbon dioxide and technical air as a direct replacement to sulphur hexafluoride (SF6) and analyses the results of PD measurement by way of internal UHF sensors and external HFCTs. The results contribute to ongoing efforts to replace the global warming gas SF6 with an alternative such as pure carbon dioxide or technical air and are applicable to mixtures of electronegative gases that have a high content of buffer gas including carbon dioxide. The experiments undertaken involved filling a full-scale gas insulated line demonstrator with different pressures of CO2 or technical air and applying voltages up to 242 kV in both clean conditions and particle contaminated conditions. The results show that carbon dioxide and technical air can insulate a gas section normally insulated with SF6 at phase-to-earth voltage of 242 kV and that both HFCT and UHF sensors can be used to detect partial discharge with natural gases. The internal UHF sensors show the most accurate PD location results but external HFCTs offer a good compromise and very similar location accuracy

Analysis of gaseous by-products of CF3I and CF3I-CO2 after high voltage arcing using a GCMS

Increasing demand for an alternative insulation medium to sulphur hexafluoride (SF6) has led to the investigation of new environmentally friendly insulation gases which could be used in high voltage equipment on the electrical power network. One such alternative, which is currently being explored by researchers, is Trifluoroiodomethane (CF3I) which could potentially be used in a gas mixture with carbon dioxide (CO2) as an insulation medium. In this paper an analysis of gaseous by-products detected as a result of high voltage breakdown through pure CF3I and a CF3I-CO2 gas mixture across a sphere-sphere electrode arrangement is given. Gas chromatography and mass spectrometry (GCMS) is used to identify the gaseous by-products produced as a result of high voltage arcing which causes the gas between the electrodes to dissociate. Analysing these gas by-products helps to identify the long-term behaviour of the gas mixture in high voltage equipment

CF3I Gas Mixtures: Breakdown Characteristics and Potential for Electrical Insulation

SF6 is a potent greenhouse gas, and there has been research into more environmentally friendly alternative gases with the aim of replacing the use of SF6 gas in high-voltage equipment. So far, the research into alternative gases has shown that CF3I gas mixtures have promising dielectric properties comparable to those of SF6. This paper provides an overview of research into CF3I gas and its mixtures, and gives an insight into its key properties. These include laboratory tests on the gas mixtures and initial applications to electrical power equipment. The insulation capability makes CF3I a feasible alternative to SF6 as an insulation medium where arc quenching is not required. On the other hand, iodine deposition after electrical discharge means CF3I may not be a suitable arc quenching gas for switchgear applications that require high current interruption unless a solution is found for controlled capture of the iodine