US 20080135817A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2008/0135817 A1 Luly et al. (43) Pub. Date: Jun. 12, 2008 (54) GASEOUS DIELECTRICS WITH LOW (22) Filed: Dec. 12, 2006 GLOBAL WARMING POTENTIALS Publication Classification (75) Inventors: Matthew H. Luly, Hamburg, NY (51) Int. Cl. (US); Robert G. Richard, HOIB 3/20 (2006.01) Hamburg, NY (US) (52) U.S. Cl. ........................................................ 252/571 Correspondence Address: (57) ABSTRACT Honeywell International Inc. A dielectric gaseous compound which exhibits the following Patent Services Department properties: a boiling point in the range between about -20° 101 Columbia Road C. to about -273°C.; non-ozone depleting; a GWP less than Morristown, NJ 07962 about 22,200; chemical stability, as measured by a negative standard enthalpy of formation (dElf<0); a toxicity level such (73) Assignee: Honeywell International Inc. that when the dielectric gas leaks, the effective diluted con centration does not exceed its PEL; and a dielectric strength (21) Appl. No.: 11/637,657 greater than air. US 2008/O 135817 A1 Jun. 12, 2008 GASEOUS DELECTRICS WITH LOW –63.8°C., which allows pressures of 400 kPa to 600 kPa (4 GLOBAL WARMING POTENTIALS to 6 atmospheres) to be employed in SF-insulated equip ment. It is easily liquefied underpressure at room temperature 1. FIELD allowing for compact storage in gas cylinders. It presents no handling problems, is readily available, and reasonably inex 0001. The present disclosure relates generally to a class of pensive. gaseous dielectric compounds having low global warming 0006 SF replaced air as a dielectric in gas insulated potentials (GWP). In particular, such gaseous dielectric com equipment based on characteristics such as insulation ability, pounds exhibits the following properties: a boiling point in boiling point, compressibility, chemical stability and non the range between about -20°C. to about -273° C.; low, toxicity. They have found that pure SF, or SF-nitrogen preferably non-ozone depleting; a GWP less than about mixtures are the best gases to date. 22,200; chemical stability, as measured by a negative stan 0007. However, SF has some undesirable properties: it dard enthalpy of formation (dHf<0); a toxicity level such that can form highly toxic and corrosive compounds when Sub when the dielectric gas leaks, the effective diluted concentra jected to electrical discharges (e.g., SF SOF); non-polar tion does not exceed its PEL, e.g., a PEL greater than about contaminants (e.g., air, CF) are not easily removed from it: 0.3 ppm by Volume (i.e., an Occupational Exposure Limit its breakdown Voltage is sensitive to water vapor, conducting (OEL or TLV) of greater than about 0.3 ppm); and a dielectric particles, and conductor Surface roughness; and it exhibits strength greater than air. These gaseous dielectric compounds non-ideal gas behavior at the lowest temperatures that can be are particularly useful as insulating-gases for use with elec encountered in the environment, i.e., in cold climatic condi trical equipment, such as gas-insulated circuit breakers and tions (about -50° C.). SF becomes partially liquefied at current-interruption equipment, gas-insulated transmission normal operating pressures (400 kPa to 500 kPa). SF is also lines, gas-insulated transformers, or gas-insulated Substa an efficient infrared (IR) absorber and due to its chemical tions. inertness, is not rapidly removed from the earth's atmosphere. Both of these latter properties make SF a potent greenhouse 2. BACKGROUND gas, although due to its chemical inertness (and the absence of 0002 Sulfur hexafluoride (SF) has been used as a gas chlorine and bromine atoms in the SF molecule) it is benign eous dielectric (insulator) in high Voltage equipment since the with regard to stratospheric ozone depletion. 1950s. It is now known that SF6 is a potent greenhouse 0008 That is, greenhouse gases are atmospheric gases Warming gas with one of the highest global Warming poten which absorb a portion of the infrared radiation emitted by the tials (GWP) known. Because of its high GWP, it is being earth and return it to earth by emitting it back. Potent green phased out of all frivolous applications. However, there is house gases have strong infrared absorption in the wavelength currently no known Substitute for SF in high Voltage equip range from approximately 7 um to 13 Jum. They occur both ment. The electrical industry has taken steps to reduce the naturally in the environment (e.g., H2O, CO., CH, NO)and leak rates of equipment, monitor usage, increase recycling, as man-made gases that may be released (e.g., SF, perfluori and reduce emissions to the atmosphere. However, it would nated compound (PFC); combustion products such as CO, still be advantageous to find a substitute for SF in electrical nitrogen, and Sulfur oxides). The effective trapping of long dielectric applications. wavelength infrared radiation from the earth by the naturally 0003. The basic physical and chemical properties of SF, occurring greenhouse gases, and its reradiation back to earth, its behavior in various types of gas discharges, and its uses by results in an increase of the average temperature of the earth's the electric power industry have been broadly investigated. Surface. Mans impact on climate change is an environmental 0004. In its normal state, SF is chemically inert, non issue that has prompted the implementation of the Kyoto toxic, non-flammable, non-explosive, and thermally stable (it Protocol regulating the emissions of man made greenhouse does not decompose in the gas phase attemperatures less than gases in a number of countries. 500° C.). SF exhibits many properties that make it suitable 0009 SF is an efficient absorber of infrared radiation, for equipment utilized in the transmission and distribution of particularly at wavelengths near 10.5 Lum. Additionally, electric power. It is a strong electronegative (electron attach unlike most other naturally occurring greenhouse gases (e.g., ing) gas both at room temperature and at temperatures well CO, CH). SF is only slowly decomposed; therefore its above ambient, which principally accounts for its high dielec contribution to global warming is expected to be cumulative tric strength and good arc-interruption properties. The break and long lasting. The strong infrared absorption of SF and its down Voltage of SF is nearly three times higher than air at long lifetime in the environment are the reasons for its atmospheric pressure. Furthermore, it has good heat transfer extremely high global warming potential which for a 100 properties and it readily reforms itself when dissociated under year time horizon is estimated to be approximately 22.200 high gas-pressure conditions in an electrical discharge or an times greater (per unit mass) than that of CO, the predomi arc (i.e., it has a fast recovery and it is self-healing). Most of nant contributor to the greenhouse effect. The concern about its stable decomposition byproducts do not significantly the presence of SF in the environment derives exclusively degrade its dielectric strength and are removable by filtering. from this very high value of its potency as a greenhouse gas. It produces no polymerization, carbon, or other conductive 0010. Accordingly, many in the electrical equipment deposits during arcing, and its is chemically compatible with industry have spent Substantial time and effort seeking Suit most Solid insulating and conducting materials used in elec able replacement gases to reduce the use of SF in high Volt trical equipment attemperatures up to about 200° C. age electrical equipment. To date, the possible replacement 0005 Besides it good insulating and heat transfer proper gases have been identified as (i) mixtures of SF and nitrogen ties, SF has a relatively high pressure when contained at for which a large amount of research results are available; (ii) room temperature. The pressure required to liquefy SF at 21° gases and mixtures (e.g., pure nitrogen, low concentrations of C. is about 2100 kPa; its boiling point is reasonably low, SF in N, and SF. He mixtures) for which a smaller yet US 2008/O 135817 A1 Jun. 12, 2008 significant amount of data is available; and (iii) potential trifluoro-nitroso-ethene?/Trifluor-nitroso-aethen gases for which little experimental data is available. 0011. Some replacements which have been proposed have Tetrafluoroethene higher GWPs than SF. For example, CFSF's falls into this 0017 3,3,4,4-tetrafluoro-3,4-dihydro-1,2diazete category. Because of fugitive emissions in the manufacture, transportation, filling and use of Such chemicals, they should (Difluoramino)difluoracetonitril be avoided. Tetrafluorooxirane 0012 However, the present inventors have determined that given the environmental difficulty of SF, it is necessary to Trifluoroacetyl fluoride relax certain of the requirements traditionally held as impor Perfluorimethylfluorformiat tant and accept as an alternative gas, compromise candidates with a lower GWP. For example, gases which are non-toxic 0018 trifluoro-acetyl hypofluorite are often inert with long atmospheric lifetimes which can perfluoro-2-aza-1-propene yield high GWP. By accepting a somewhat more reactive gas than SF, the GWP can be greatly reduced. It may also be Perfluor-2-aza-1-propen (germ.) necessary to accept slightly more toxic materials in order to find the best alternative in these applications. Such an N-Fluor-tetrafluor-1-aethanimin (germ.) increase intoxicity can be offset by reducing equipment leak 0019. 3.3-difluoro-2-trifluoromethyl-oxaziridine rates or installing monitoring equipment. In some cases, the bis-trifluoromethyl-diazene/hexafluoro-icis-azomethane gases discovered by the present inventors as Suitable alterna tives to SF are show to be efficient at low levels and can be Fluoroxypentafluoroethane mixed with nitrogen and/or another non-toxic gas to give dielectrics with greatly reduced toxicity and acceptably low (0020 bis-trifluoromethyl peroxide GWPS.