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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Seismic Resilience of Large Power Transformer Bushings & Non-SF6 Industrial Base Scan Review

Large (high voltage) power transformers (LPT), and more specifically, their bushings, are known to be susceptible to seismic failure. With bushing failure, a transformer will have to be replaced, which has a considerable lead time, adding to the power outage duration. Cost-efficient, proven solutions are not currently available to mitigate this risk, which can persist for the more than 30-year life of a particular transformer. This work will focus on developing and demonstrating a hardware solution to address seismic vulnerabilities and reduce outage risks from LPT failure. Sulfur Hexafluoride (SF6) is a specialty gas with excellent electrical insulation properties which has been used extensively in the power industry. This gas is unfortunately also one of the most potent greenhouse gases known to humanity. A 2014 report by the Intergovernmental Panel on Climate Change found that SF6 has a global warming potential (GWP) 23,000 times higher than Carbon Dioxide, and has the highest GWP of all gases assessed (Myhre 2013). SF6 is almost exclusively man-made and is produced for use as an insulator in high voltage electrical equipment. This makes the production and use of SF6 one of the leading sources of anthropogenic climate change. To fully eliminate the environmental impacts of SF6, alternative technology is needed. The ideal replacement would be a technology that can fulfil the same role as SF6, at the same cost or cheaper, but without adverse environmental effects. Currently, no technology fits this description, however several promising technologies have begun to enter the market. An industry scan was performed to assess the state of industry adoption and manufacturing capability for SF6-free alternative technologies for use at the high-voltage level, and the primary barriers to broader adoption.

10 SYNTHETIC FUELS↗
DOE OSTI2023

Investigation of SF6 Alternatives in Spark Gap Switches for GWP Reduction

This primary purpose of this project was to evaluate alternative gas mixtures to sulfur hexafluoride (SF6) developed for high voltage power delivery applications for use in high voltage spark gap switches. These SF6 alternatives lower global warming potential emissions and enable improvements to the pressure-voltage design space. A combined experimental, computational, and theoretical study was used to quantify the impact of persistent breakdown products on the breakdown distribution of SF6-replacement gas mixtures. Viable SF6 replacements suitable for use in spark gap switches were studied to enable performance and agility improvements for next-generation pulsed power research relevant to national security missions. Experimental campaign included establishing parameters of switch gases as function of concentration. Various concentrations and pressures were tested for trends in breakdown voltage, repeatability, and durability, and breakdown constituents. A zero-dimensional plasma global model was used to simulate the plasma arc decay and recombination process in spark-gap switches relevant to the Z machine. Finally, a complete and consistent set of electron-neutral collision cross-sections for the novel insulating gas C4F7N is reported.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Decomposition characteristics of C4F7N-based SF6-alternative gas mixtures

C4F7N [2,3,3,3-tetrafluoro-2-(trifluoromethyl)propanenitrile]/CO2 gas mixtures are being developed as an eco-friendly electrical insulator to replace SF6, the most potent greenhouse industrial gaseous dielectric. However, recent studies have reported complicated and often conflicting decomposition pathways for C4F7N/CO2 gas mixtures, which has raised concerns. In this work, the decomposition characteristics of C4F7N/CO2 gas mixtures were studied comprehensively by both designed computations and experiments. Computations were performed starting from fundamental propositions of C4F7N/CO2 decompositions, which were further experimentally verified by pyrolysis, long-term thermal aging with/without catalytic materials (industrial-grade molecular sieves 4A), and electrical decomposition by spark discharge. The results of both computations and experiments suggest that in an ideal thermal decomposition, C4F7N is likely to decompose into C2F6 and small fluoronitriles first at high temperatures. The generation of C3F6 and C2N2 from C4F7N thermal decomposition at lower temperatures appears because of the catalytic effect of incompatible materials, for example, the industrial-grade molecular sieves 4A that we tested. The electron impact dissociation of C4F7N plays an important role in C4F7N electrical decomposition, leading to additional formation of distinctive small molecules of CF4 and C2N2 of low concentrations. It was pointed out based on a real arcing test in a load disconnector that the decomposition of C4F7N gas mixtures in real applications will be at a much moderate and manageable rate than what was obtained from the highly accelerated laboratory tests presented in this work. The signatures of decomposition products extracted in this study provide invaluable guidance for developing decomposition-based diagnosis and fixation of decomposition byproducts toward SF6-free power grids.

Physics↗
DOE OSTI2024

SF6 Negative Ion Formation in Charge Transfer Experiments

In the present work, we report an update and extension of the previous ion-pair formation study of Hubers, M.M.; Los, J. Chem. Phys. 1975, 10, 235–259, noting new fragment anions from time-of-flight mass spectrometry. The branching ratios obtained from the negative ions formed in K + SF6 collisions, in a wide energy range from 10.7 up to 213.1 eV in the centre-of-mass frame, show that the main anion is assigned to SF5− and contributing to more than 70% of the total ion yield, followed by the non-dissociated parent anion SF6− and F−. Other less intense anions amounting to <20% are assigned to SF3− and F2−, while a trace contribution at 32u is tentatively assigned to S− formation, although the rather complex intramolecular energy redistribution within the temporary negative ion is formed during the collision. An energy loss spectrum of potassium cation post-collision is recorded showing features that have been assigned with the help of theoretical calculations. Quantum chemical calculations for the lowest-lying unoccupied molecular orbitals in the presence of a potassium atom are performed to support the experimental findings. Apart from the role of the different resonances participating in the formation of different anions, the role of higher-lying electronic-excited states of Rydberg character are noted.

Biochemistry & Molecular Biology↗
DOE OSTI2020

Materials Data on SF6 by Materials Project

SF6 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of three sulfur hexafluoride molecules. S6+ is bonded in an octahedral geometry to six F1- atoms. All S–F bond lengths are 1.59 Å. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one S6+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one S6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SF6 by Materials Project

SF6 is Tungsten structured and crystallizes in the cubic Im-3m space group. The structure is zero-dimensional and consists of two sulfur hexafluoride molecules. S6+ is bonded in an octahedral geometry to six equivalent F1- atoms. All S–F bond lengths are 1.60 Å. F1- is bonded in a single-bond geometry to one S6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SF6 by Materials Project

SF6 crystallizes in the trigonal P-3m1 space group. The structure is zero-dimensional and consists of three sulfur hexafluoride molecules. S6+ is bonded in an octahedral geometry to six equivalent F1- atoms. All S–F bond lengths are 1.60 Å. F1- is bonded in a single-bond geometry to one S6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs3H(SF6)2 by Materials Project

Cs3H(SF6)2 crystallizes in the orthorhombic Pba2 space group. The structure is three-dimensional. there are two inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 8-coordinate geometry to two equivalent H1+ and fourteen F1- atoms. There are one shorter (3.24 Å) and one longer (3.42 Å) Cs–H bond lengths. There are a spread of Cs–F bond distances ranging from 3.19–3.65 Å. In the second Cs1+ site, Cs1+ is bonded in a 12-coordinate geometry to twelve F1- atoms. There are a spread of Cs–F bond distances ranging from 3.05–3.61 Å. H1+ is bonded in a linear geometry to two equivalent Cs1+ and two equivalent F1- atoms. Both H–F bond lengths are 1.14 Å. S4+ is bonded in a square pyramidal geometry to five F1- atoms. There are a spread of S–F bond distances ranging from 1.63–1.80 Å. There are six inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to four Cs1+ and one H1+ atom. In the second F1- site, F1- is bonded in a distorted single-bond geometry to three Cs1+ and one S4+ atom. In the third F1- site, F1- is bonded in a distorted single-bond geometry to three Cs1+ and one S4+ atom. In the fourth F1- site, F1- is bonded in a distorted single-bond geometry to three Cs1+ and one S4+ atom. In the fifth F1- site, F1- is bonded in a distorted single-bond geometry to three Cs1+ and one S4+ atom. In the sixth F1- site, F1- is bonded in a single-bond geometry to three Cs1+ and one S4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Industry Scan of Non-SF6 Gas-Insulated Technologies

Sulfur Hexafluoride (SF 6 ) is a specialty gas with excellent electrical insulation properties which has been used extensively in the power industry. This gas is unfortunately also one of the most potent greenhouse gases known to humanity. A 2014 report by the Intergovernmental Panel on Climate Change found that SF 6 has a global warming potential (GWP) 23,000 times higher than Carbon Dioxide, and has the highest GWP of all gases assessed (Myhre 2013). SF 6 is almost exclusively man-made and is produced for use as an insulator in high voltage electrical equipment. This makes the production and use of SF 6 one of the leading sources of anthropogenic climate change. Since SF 6 recognition as a significant contributor to climate change, most governments and organizations have sought ways to reduce or eliminate their use of this gas. Many utilities have initiated leak monitoring and repair programs which have significantly reduced emissions of this gas into the atmosphere. While leak reduction programs have been effective at reducing emission rates in the developed world, leak rates remain frozen at ~1% annually. However, one of the largest and fastest growing markets for this gas is in the developing world where emissions standards are often lacking (P&S Intelligence. 2023). To fully eliminate the environmental impacts of SF 6 , alternative technology is needed. The ideal replacement would be a technology that can fulfil the same role as SF 6 , at the same cost or cheaper, but without adverse environmental effects. Currently, no technology fits this description, however several promising technologies have begun to enter the market. This report was commissioned by the United States Department of Energy’s Office of Electricity under the Transformer Resilience and Advanced Components (TRAC) program to assess the state of industry adoption and manufacturing capability for SF 6 -free alternative technologies for use at the high-voltage level, and the primary barriers to broader adoption. While this report is tailored to the United States, the findings should be relevant to all stakeholders seeking to reduce SF 6 emissions.

24 - POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2020

Materials Data on Ge(SF6)2 by Materials Project

GeF6(SF3)2 crystallizes in the orthorhombic Pnnm space group. The structure is zero-dimensional and consists of two GeF6 clusters and four SF3 clusters. In each GeF6 cluster, Ge4+ is bonded in an octahedral geometry to six F1- atoms. There is two shorter (1.83 Å) and four longer (1.84 Å) Ge–F bond length. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one Ge4+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one Ge4+ atom. In each SF3 cluster, S4+ is bonded in a 3-coordinate geometry to three F1- atoms. There is one shorter (1.56 Å) and two longer (1.57 Å) S–F bond length. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one S4+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one S4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Investigating the Performance of SF6 Replacement Gases to Enable the Next Generation of Pulsed Power

High voltage switches are essential components in pulsed power systems, where consistent and reliable performance is crucial—particularly as the field explores alternatives to SF 6 as an insulating gas. This project examines the self-break voltage distributions of various gases, with a focus on the low-voltage discharges observed in the lower tail of these distributions. Experimental results revealed that the specific housing design influenced the self-break behavior. Among the tested gases, air demonstrated a more favorable overall distribution compared to SF 6 , albeit requiring higher operating pressures. However, air also exhibited a greater likelihood of extremely low-voltage dropouts, raising concerns about its suitability as a direct replacement for SF 6 . Notably, all gases tested showed a higher-than-expected probability of low-voltage events when considering the tail of the distribution rather than the bulk behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

SF6 / Acetone Separation & Purification

Sulfur hexafluoride (SF₆) is recognized as the most potent greenhouse gas used in the power transmission and semiconductor sectors. In the past decade, its global emissions have increased sharply, largely due to the absence of effective disposal and recovery pathways. This concern was formally addressed under the Kyoto Protocol, which urged participating nations to adopt measures to limit SF₆ emissions and mitigate its role in climate change. In recent years, various abatement strategies have been explored, including non-thermal plasma (NTP) technologies such as radio frequency, microwave, dielectric barrier discharge, and electron beam systems. While these methods can decompose SF₆, they also produce hazardous by-products like sulfur oxyfluorides, sulfur dioxide, hydrofluoric acid, and fluorine gas. Because these compounds pose both environmental and health risks, replacing traditional disposal practices with modern, more effective treatment methods has become an urgent priority.

36 MATERIALS SCIENCE↗