US007807074B2

(12) United States Patent (10) Patent N0.: US 7,807,074 B2 Luly et al. (45) Date of Patent: Oct. 5, 2010

(54) GASEOUS WITH LOW Shiojiri, et al., Abstract of “Life cycle impact assessment of various GLOBAL WARMING POTENTIALS treatment scenarios for hexa?uoride (SE 6) used as an insulat ing gas”, Environmental Progress, 2006, 25(3), 218-227. (75) Inventors: Matthew H. Luly, Hamburg, NY (U S); Shiojiri, et al., Abstract of “A Life cycle impact assessment study on Robert G. Richard, Hamburg, NY (U S) sulfur hexa?uoride (SE 6) used as a gas ”, 2004, American Institute of Chemical Engineers, 005E/1-005E/9. (73) Assignee: Honeywell International Inc., Goshima, et al., Abstract of “Estimation of cross-sectional size of gas-insulated apparatus using hybrid insulation system with SE 6 MorristoWn, N] (U S) substitute”, Gaseous Dielectrics X, 2004, pp. 253-258. ( * ) Notice: Subject to any disclaimer, the term of this Telfer, et al., Abstract of “A novel approach to power design for replacement of SE6”, Centre for Intelligent Monitoring patent is extended or adjusted under 35 Systems, Dept. of Electrical Engineering and Electronics, 2004, U.S.C. 154(b) by 803 days. 44(2), pp. 72-76. Gustavino, et al., Abstract of “Performance ofglass RPC operated in (21) App1.N0.: 11/637,657 streamer mode with four-fold gas mixtures containing SE 6’ ’, Nuclear Instruments & Methods in Physics Research, Section A: Accelera (22) Filed: Dec. 12, 2006 tors, Spectrometers, Detectors, and Associated Equipment, 2004, 517(1-3), pp. 101-108. (65) Prior Publication Data DiaZ, et al., Abstract of “Ejfect of the percentage of SE6 (100%-10% US 2008/0135817 A1 Jun. 12, 2008 5%) on the decomposition of SE6-N2 mixtures under negative dc coronas in the presence of Water vapour or ”, Journal of (51) Int. Cl. Physics D: Applied Physics, 2003, 36(13), pp. 1558-1564. H01B 3/16 (2006.01) Yanabu, et al., Abstract of “New concept of for replacing SE6 or gas mixture”, Gaseous Dielectrics IX, 9”‘, 2001, pp. 497-504. (52) US. Cl...... 252/571; 252/67; 252/68; Knobloch, et al., Abstract of “The comparison of arc-extinguishing 252/ 69 capability of sulfur hexa?uoride (SE 6) with alternative gases in (58) Field of Classi?cation Search ...... 252/67, high-voltage circuit-breakers”, Gaseous Dielectrics VIII, 8”’, 1998, 252/68, 69, 571 pp. 565-571. See application ?le for complete search history. Tioursi, et al., Abstract of “Conditioning phenomena in N2, SE 6, and air”, IEE Conference, 467 ( Engineering, vol. 3), 1999, (56) References Cited pp. 3.212-3215. U.S. PATENT DOCUMENTS Christophorou, et al., Abstract of “SE6/N2 mixtures. Basic and H V insulation properties”, IEEE Transactions on Dielectrics and Elec 2,786,804 A * 3/1957 Nelson ...... 203/50 trical Insulation, 1995, 2(5), pp. 952-1003. 4,257,905 A 3/1981 Christophorou et al. Pai, et al., Abstract of “Impulse breakdown of cis-octa?uorobutene/ 4,275,260 A 6/1981 Wootton sulfur hexa?uoride and cis-octa?uorobutene/sub’ur hexa?ouride/ni 4,288,651 A 9/1981 Wootton trogen”, Gaseous Dielectr. Proc. Int. Sump., 2nd, 1980, pp. 190-199. 4,440,971 A 4/1984 Harrold Devins, J.C., Abstract of “Replacement gases for sulfur 4,547,316 A 10/1985 Yamauchi hexa?uoride”, IEEE Transactions on Electrical Insulation, 1980, 4,816,624 A 3/1989 Perrissin et al...... 200/148 B EI-15-(2), pp. 81-86. 4,871,680 A * 10/1989 Barraud et al...... 436/103 5,236,611 A 8/1993 Shiflett Devins, et al., Abstract of “Replacement gases for sulfur hexa?uoride”, Annual ReportiConference on Electrical Insulation 5,918,140 A * 6/1999 Wickboldt et al...... 438/535 and Phenomena, 1979, pp. 398-408. 6,886,573 B2 5/2005 Hobbs et al...... 134/221 6,897,396 B2 5/2005 Ito et al...... 218/120 Rhodes, et al., Abstract of “Assessment of the possible use of 2002/0135029 A1* 9/2002 Ping et al. 257/401 polythene/gas dielectrics in high-voltage cables”, Proc. Inst. Elec. 2002/0137269 A1* 9/2002 Ping et al...... 438/197 Engrs., 1965, 112-*), pp. 1617-1624. 2003/0164513 A1* 9/2003 Ping et al...... 257/288 Howard, et al., Abstract of “Insulation properties of compressed 2005/0181621 A1* 8/2005 Borland et al. . 438/752 electronegative gases”, Proc. Inst. Elec. Engrs., 1957, 104(Pt. A), pp. 2006/0060818 A1* 3/2006 Tempel et al. 252/181.3 123-138. 2006/0133986 A1* 6/2006 Dukhedin-Lalla et al. 423/500 2009/0211449 A1* 8/2009 Olschimke et al...... 95/233 * cited by examiner Primary ExamineriDouglas Mc Ginty FOREIGN PATENT DOCUMENTS EP 0129200 A 12/1984 (57) ABSTRACT EP 1146522 X 10/2001

OTHER PUBLICATIONS A dielectric gaseous compound Which exhibits the following properties: a boiling point in the range betWeen about —200 C. CAS Reg. No. 7647-19-0, Nov. 16, 1984* to about —2730 C.; loW oZone depleting; a GWP less than Takuma, et al., “Gases as a Dielectric”, pp. 195-2004, Gaseous about 22,200; chemical stability, as measured by a negative Dielectrics X, Springer, 2004. standard enthalpy of formation (dHf<0); a toxicity level such LutZ Niemeyer, “A Systematic Search for Insulation Gases and Their that When the dielectric gas leaks, the effective diluted con Environmental Evaluation”; pp. 459-464, Gaseous Dielectrics VIII, centration does not exceed its PEL; and a 1998. greater than air. Christophorou, et al., “Gases for Electrical Insulation and Arc Inter ruption.‘ Possible Present and Future Alternatives to Purse SE ”, NIST Technical Note 1425, Nov. 1997. 2 Claims, No Drawings US 7,807,074 B2 1 2 GASEOUS DIELECTRICS WITH LOW easily lique?ed under pressure at room temperature alloWing GLOBAL WARMING POTENTIALS for compact storage in gas cylinders. It presents no handling problems, is readily available, and reasonably inexpensive. FIELD SP6 replaced air as a dielectric in gas insulated equipment based on characteristics such as insulation ability, boiling The present disclosure relates generally to a class of gas point, compressibility, chemical stability and non-toxicity. eous dielectric compounds having loW global Warming poten They have found that pure SP6, or SF6-nitro gen mixtures are tials (GWP). In particular, such gaseous dielectric com pounds exhibits the folloWing properties: a boiling point in the best gases to date. the range betWeen about —20° C. to about —273° C.; loW, HoWever, SP6 has some undesirable properties: it can form preferably non-oZone depleting; a GWP less than about highly toxic and corrosive compounds When subjected to 22,200; chemical stability, as measured by a negative stan electrical discharges (e.g., $21310, SOFZ); non-polar contami dard enthalpy of formation (dHf<0); a toxicity level such that nants (e.g., air, CF4) are not easily removed from it; its break When the dielectric gas leaks, the effective diluted concentra doWn voltage is sensitive to Water vapor, conducting particles, tion does not exceed its PEL, e.g., a PEL greater than about and conductor surface roughness; and it exhibits non-ideal 0.3 ppm by volume (i.e., an Occupational Exposure Limit gas behavior at the loWest temperatures that can be encoun (OEL or TLV) of greater than about 0.3 ppm); and a dielectric tered in the environment, i.e., in cold climatic conditions strength greater than air. These gaseous dielectric compounds (about —50° C.), SP6 becomes partially lique?ed at normal are particularly useful as insulating-gases for use With elec operating pressures (400 kPa to 500 kPa). SP6 is also an trical equipment, such as gas-insulated circuit breakers and 20 e?icient infrared (IR) absorber and due to its chemical inert current-interruption equipment, gas-insulated transmission ness, is not rapidly removed from the earth’s atmosphere. lines, gas-insulated , or gas-insulated substa Both of these latter properties make SP6 a potent greenhouse tions. gas, although due to its chemical inertness (and the absence of and bromine atoms in the SP6 molecule) it is benign BACKGROUND 25 With regard to stratospheric oZone depletion. That is, greenhouse gases are atmospheric gases Which Sulfur hexa?uoride (SP6) has been used as a gaseous absorb a portion of the infrared radiation emitted by the earth dielectric (insulator) in high voltage equipment since the and return it to earth by emitting it back. Potent greenhouse 1950s. It is noW knoWn that SP6 is a potent greenhouse Warming gas With one of the highest global Warming poten gases have strong infrared absorption in the Wavelength range 30 from approximately 7 um to 13 pm. They occur both naturally tials (GWP) knoWn. Because of its high GWP, it is being phased out of all frivolous applications. However, there is in the environment (e.g., H2O, CO2, CH4, N20) and as man currently no knoWn substitute for SP6 in high voltage equip made gases that may be released (e.g., SP6; per?uorinated compound (PFC); combustion products such as CO2, nitro ment. The electrical industry has taken steps to reduce the gen, and sulfur oxides). The effective trapping of long-Wave leak rates of equipment, monitor usage, increase recycling, 35 length infrared radiation from the earth by the naturally and reduce emissions to the atmosphere. HoWever, it Would occurring greenhouse gases, and its reradiation back to earth, still be advantageous to ?nd a substitute for SP6 in electrical dielectric applications. results in an increase of the average temperature of the earth’ s The basic physical and chemical properties of SP6, its surface. Mans impact on climate change is an environmental issue that has prompted the implementation of the Kyoto behavior in various types of gas discharges, and its uses by the 40 electric poWer industry have been broadly investigated. Protocol regulating the emissions of man made greenhouse gases in a number of countries. In its normal state, SP6 is chemically inert, non-toxic, non ?ammable, non-explosive, and thermally stable (it does not SP6 is an e?icient absorber of infrared radiation, particu decompose in the gas phase at temperatures less than 500° larly at Wavelengths near 10.5 um. Additionally, unlike most C.). SP6 exhibits many properties that make it suitable for 45 other naturally occurring green house gases (e.g., CO2, CH4), equipment utiliZed in the transmission and distribution of SP6 is only sloWly decomposed; therefore its contribution to electric poWer. It is a strong electronegative (electron attach global Warming is expected to be cumulative and long lasting. ing) gas both at room temperature and at temperatures Well The strong infrared absorption of SP6 and its long lifetime in above ambient, Which principally accounts for its high dielec the environment are the reasons for its extremely high Which for a l00-year time horiZon is esti tric strength and good arc-interruption properties. The break 50 doWn voltage of SP6 is nearly three times higher than air at mated to be approximately 22,200 times greater (per unit atmospheric pressure. Furthermore, it has good heat transfer mass) than that of CO2, the predominant contributor to the properties and it readily reforms itself When dissociated under greenhouse effect. The concern about the presence of SP6 in high gas-pressure conditions in an electrical discharge or an the environment derives exclusively from this very high value of its potency as a greenhouse gas. arc (i.e., it has a fast recovery and it is self-healing). Most of 55 its stable decomposition byproducts do not signi?cantly Accordingly, many in the electrical equipment industry degrade its dielectric strength and are removable by ?ltering. have spent substantial time and effort seeking suitable It produces no polymerization, carbon, or other conductive replacement gases to reduce the use of SP6 in high voltage deposits during arcing, and its is chemically compatible With electrical equipment. To date, the possible replacement gases most solid insulating and conducting materials used in elec 60 have been identi?ed as (i) mixtures of SP6 and for trical equipment at temperatures up to about 200° C. Which a large amount of research results are available; (ii) Besides it good insulating and heat transfer properties, SP6 gases and mixtures (e. g., pure nitrogen, loW concentrations of has a relatively high pressure When contained at room tem SP6 in N2, and SF6iHe mixtures) for Which a smaller yet perature. The pressure required to liquefy SP6 at 21° C. is signi?cant amount of data is available; and (iii) potential about 2100 kPa; its boiling point is reasonably loW, —63.8° C., 65 gases for Which little experimental data is available. Which alloWs pressures of 400 kPa to 600 kPa (4 to 6 atmo Some replacements Which have been proposed have higher spheres) to be employed in SF6-insulated equipment. It is GWPs than SP6. For example, CF3SF5 falls into this category. US 7,807,074 B2 3 4 Because of fugitive emissions in the manufacture, transpor tation, ?lling and use of such chemicals, they should be 3 -?uoro -3 #H! -diaZirine-3-carbonitrile avoided. Ethyne However, the present inventors have determined that given 1,2,2-tri?uoro -aZiridine the environmental di?iculty of SP6, it is necessary to relax Ketene certain of the requirements traditionally held as important and (di?uoro)vinylboran accept as an alternative gas, compromise candidates With a (Di?uor)vinylboran (germ.) loWer GWP. For example, gases Which are non-toxic are often tri?uoro-vinyl-silane inert With long atmospheric lifetimes Which can yield high Ethinylsilan GWP. By accepting a someWhat more reactive gas than SP6, ethyl-di?uor-borane the GWP can be greatly reduced. It may also be necessary to Ethyl-di?uor-boran (germ.) accept slightly more toxic materials in order to ?nd the best methyl-methylen-amine alternative in these applications. Such an increase in toxicity Dimethyl ether can be offset by reducing equipment leak rates or installing vinyl-silane monitoring equipment. In some cases, the gases discovered Dimethylsilane by the present inventors as suitable alternatives to SP6 are Chloroethyne shoW to be ef?cient at loW levels and can be mixed With nitrogen and/ or another non-toxic gas to give dielectrics With Ethanedinitrile greatly reduced toxicity and acceptably loW GWPs. tetra?uoropropyne// l ,3 ,3 ,3 -tetra?uoropropyne The unique gaseous compounds discovered by the present 20 hexa?uoro-oxetane inventors for use as substitutes for SP6 can be used in some existing electrical equipment, although they Would preferably be used in speci?c electrical equipment optimiZed for them. penta?uoro-propionyl ?uoride//per?uoropropionyl ?uoride The gaseous compounds of the present disclosure are prefer Tri?uoromethyl tri?uorovinyl ether ably used in pure form, but can also be used as part of an 25 1 -Propyne aZeotrope, or a mixture With an appropriate second gas, such Cyclopropane as nitrogen, CO2 or N20. Propane Trimethylborane SUMMARY cyanoketene 30 butatriene A dielectric gaseous compound Which exhibits the folloW Cyano-bispenta?uorethyl-phosphin ing properties: a boiling point in the range betWeen about Trimethyl- l , l ,2,2-tetra?uorethylsilan —200 C. to about —2730 C.; loW, preferably non-oZone deplet methyl diborane ing; a GWP less than about 22,200; chemical stability, as Methyldiboran (germ.) measured by a negative standard enthalpy of formation 35 carbonyl bromide ?uoride (dHf<0); a toxicity level such that When the dielectric gas chloro-di?uoro-nitroso-methane//Chlor-di?uor-nitroso leaks, the effective diluted concentration does not exceed its methan PEL (i.e., an Occupational Exposure Limit (OEL or TLV) of chloroperoxytri?uoromethane at least about 0.3 ppm); and a dielectric strength greater than carbonylchlorid-?uorid air. 40 Carbonychlorid?uorid (germ.) The dielectric gaseous compound is at least one compound selected from the group consisting of: di?uoro diaZomethane Arsenic penta?uoride Di?uordiaZomethan (germ.) Arsine Carbonyl ?uoride Diboron tetra?uoride 45 Di?uordioxiran Diborane Perchloric acid, 2-chloro-l,l,2,2-tetra?uoroethyl ester (9C1) tri?uoromethylaZide Perchloric acid, l,2,2-trichloro-l,2-di?uoroethyl ester Tri?uormethylaZid (germ.) Tri?uoroacetyl chloride tetra?uoro-diaZiridine tri?uoromethylisocyanide (CF3-NC) 50 Fluorperoxytri?uormethan tri?uoromethyl isocyanide tri?uoro-nitroso-ethene//Tri?uor-nitroso-aethen Tri?uormethyl-phosphonyl?uorid Tetra?uoroethene Cyanogen ?uoride Tri?uormethylphosphane (germ.) 55 DiaZomethane Tetra?uorooxirane formaldehyde//Formalin (methyl)di?uoroborane (Methyl)di?uorboran (germ.) Chloromethane per?uoro-2-aZa-l -propene 60 methylphosphonous acid di?uoride//di?uoro-methyl-phos Per?uor-2-aZa- l -propen (germ.) phine N-Fluor-tetra?uor-l -aethanimin (germ.) tri?uoro-methoxy-silane 3,3-di?uoro-2-tri?uoromethyl-oxaZiridine bis -tri?uoromethyl -diaZene//hexa?uoro -#ci s! -aZomethane Methane Fluoroxypenta?uoroethane 65 Methylsilane bis-tri?uoromethyl peroxide #Si ! -bromo-#Si ! ,#Si ! '-methanediyl-bis-silane

US 7,807,074 B2 1 0 sul?de Chlordi?uordi?uoraminomethan thiocarbonyl di?uoride Thiocarbonyldi?uorid (germ.) Hydrogen iodide selenocarbonyl di?uoride Krypton Tri?uoroiodomethane Nitrogen N-Fluor-di?uormethanimin (germ.) tri?uoro-nitroso-methane//Tri?uor-nitroso-methan Nitrogen oxide; and tri?uoro-nitro-methane//Tri?uor-nitro-methan//?uoropicrin 10 Xenon Tetra?uoromethane The dielectric gaseous compound is optionally formed as Tetra?uorformamidin (ger'm.) an aZeotrope, Which imparts many advantages in handling the tetra?uorourea mixture. Preferred mixtures for dielectric gaseous compound hypo?uorous acid tri?uoromethyl ester//Hypo?uorigsaeure contain one additional gas selected from the group consisting tri?uormethylester//tri?uoromethyl hypo?uorite of: nitrogen, CO2 and N20. tri?uoromethanesulfonyl ?uoride The present disclosure also includes an insulation-gas for use in electrical equipment, Wherein said insulation-gas is a dielectric gaseous compound Which exhibits the folloWing properties: a boiling point in the range betWeen about —200 C. sulfurcyanide penta?uoride 20 to about —2730 C.; loW, preferably non-oZone depleting; a SchWefelcyanid-penta?uorid (ger'm.) GWP less than about 22,200; chemical stability, as measured di?uoro-tri?uoromethyl-phosphine by a negative standard enthalpy of formation (dHf<0); a tox Hexa?uormethandiamin icity level such that When the dielectric gas leaks, the effective per?uoro methyl silane diluted concentration does not exceed its PEL (i.e., Occupa Per?uormethylsilan (germ.) 25 tional Exposure Limit (OEL or TLV) of at least about 0.3 Tri?uormethyl-tetra?uorphosphoran (germ.) ppm); and a dielectric strength greater than air. Di?uoromethane Preferably, the electrical equipment is at least one selected Fluoroiodomethane from the group consisting of: gas-insulated circuit breakers ?uoromethane//methyl ?uoride// Fluor-methan/ / freon-41 and current-interruption equipment, gas-insulated transmis tri?uoromethyl-silane" CF3SiH3 30 sion lines, gas-insulated transformers, and gas-insulated sub methyltri?uorosilane stations. di?uoro-methyl-silane ?uoro-methyl-silane DETAILED DESCRIPTION OF THE PREFERRED methylgermane EMBODIMENT Di?uorformimin 35 Tri?uoromethane The compounds of the present disclosure are useful in tri?uoromethane thiol gaseous phase for electrical insulation and for arc quenching Tri?uormethanthiol (germ.) and current interruption equipment used in the transmission and distribution of electrical energy. Generally, there are four di?uoro dichlorosilane 40 major types of electrical equipment Which the gases of the Di?uordichlorsilan (ger'm.) present disclosure can be used for insulation and/or interrup di?uoro chlorosilane tion purposes: (1) gas-insulated circuit breakers and current Di?uorchlorsilan (ger'm.) interruption equipment, (2) gas-insulated transmission lines, Phosphorus chloride di?uoride (3) gas-insulated transformers, and (4) gas-insulated substa Chlorotri?uorosilane 45 tions. Such gas-insulated equipment is a major component of Hydrogen chloride poWer transmission and distribution systems all over the Chlorosilane World. It offers signi?cant savings in land use, is aesthetically acceptable, has relatively loW radio and audible noise emis sions, and enables substations to be installed in populated Carbonyl sul?de 50 areas close to the loads. Depending on the particular function of the gas-insulated trans-Di?uorodiaZine equipment, the gas properties Which are the most signi?cant cis-Di?uorodiaZine vary. Thionyl ?uoride For circuit breakers the excellent thermal conductivity and Tri?uorosilane 55 high dielectric strength of such gases, along With the fast Nitrogen tri?uoride thermal and dielectric recovery (short time constant for Tri?uoramine oxide increase in resistivity), are the main reasons for its high inter thiaZyl tri?uoride ruption capability. These properties enable the gas to make a Phosphorus tri?uoride rapid transition betWeen the conducting (arc ) and the Germanium(IV) ?uoride 60 dielectric state of the arc, and to Withstand the rise of the Tetrafuorosilane recovery voltage. Phosphorus penta?uoride For gas-insulated transformers the cooling ability, compat Selenium hexa?uoride ibility With solid materials, and partial discharge characteris Tellurium hexa?uoride tics, added to the dielectric characteristics, make them a desir ?uorosilane 65 able medium for use in this type of electrical equipment. The Nitrosyl ?uoride compounds have distinct advantages over oil insulation, nitrate including none of the ?re safety problems or environmental US 7,807,074 B2 11 12 problems related to oil, high reliability, ?exible layout, little in?uences, such as electrical breakdown and discharges. To maintenance, long service life, loWer noise, better handling, be used in electrical applications, a dielectric gas should: and lighter equipment. (undergo no extensive decomposition; lead to no polymeriza For gas-insulated transmission lines the dielectric strength tion; form no carbon or other deposits; and be non-corrosive of the gaseous medium under industrial conditions is of para and non-reactive to metals, insulators, spacers, and seals. In mount importance, especially the behavior of the gaseous addition it should have: no byproduct With toxicity unaccept dielectric under metallic particle contamination, sWitching able for industrial applications; removable byproducts; and a and lightning impulses, and fast transient electrical stresses. high recombination rate for reforming itself, especially for These gases also have a high ef?ciency for transfer of heat arc interruption. Finally, the gas must be environmentally from the conductor to the enclosure and are stable for long friendly, e.g., it must not contribute to global Warming, must periods of time (e. g., 40 years). These gas-insulated transmis not deplete stratospheric oZone, and must not persist in the sion lines offer distinct advantages: cost effectiveness, high carrying capacity, loW losses, availability at all voltage rat environment for long periods of time. ings, no ?re risk, reliability, and a compact alternative to Speci?c properties of the gas under discharge and break overhead high voltage transmission lines in congested areas doWn conditions include: a high under that avoids public concerns With overhead transmission lines. uniform and non-uniform electric ?elds; insensitivity to sur For gas-insulated substations, the entire substation (circuit face roughness or defects and freely moving conducting par breakers, disconnects, grounding sWitches, busbar, trans ticles; good insulation properties under practical conditions; formers, etc., are interconnected) is insulated With the gas good insulator ?ashover characteristics; good heat transfer eous dielectric medium of the present disclosure, and, thus, 20 characteristics; good recovery (rate of voltage recovery) and all of the above-mentioned properties of the dielectric gas are self-healing; no adverse reactions With moisture and common signi?cant. impurities; and no adverse effects on equipment, especially The properties of a dielectric gas that are necessary for its on spacers and electrode surfaces. use in high voltage equipment are many and vary depending Speci?c properties of gaseous insulators for speci?c elec on the particular application of the gas and the equipment. 25 trical equipment is set forth beloW: Intrinsic properties are those properties of a gas Which are Circuit breakersiThe most signi?cant required gas proper inherent in the physical atomic or molecular structure of the ties for arc interruption are: (i) high dielectric strength gas. These properties are independent of the application or the comparable to that of SP6; (ii) high thermal conductivity; environment in Which a gas is placed. One of the desirable (iii) fast gas recovery; and (iv) self-healing/dielectric integ properties of a gaseous dielectric is high dielectric strength 30 rity. (higher, for instance than air). The gas properties that are principally responsible for high dielectric strength are those Gas-insulated transmission linesiThe required properties that reduce the number of electrons Which are present in an include: (i) high dielectric strength; (ii) high vapor pres sure electrically-stressed dielectric gas. To effect such a reduction at operating and ambient temperature; (iii) chemical inert in the electron number densities, as gas should: (i) be elec 35 ness; (iv) high thermal conductivity; (v) no thermal aging; tronegative (remove electrons by attachment over as Wide an (vi) no deposits; (vii) easily removable, non-harmful energy range as possible); it should preferably exhibit byproducts; and (viii) no unacceptable level of haZards increased electron attachment With increasing electron (?re, explosion, toxicity, corrosion). energy and gas temperature since electrons have a broad Gas-insulated transformersiThe properties of the gas range of energies and the gas temperature in many applica 40 required for this application include: (i) high dielectric tions is higher than ambient; (ii) have good electron sloWing strength at reasonable pressures (e.g., 500 kPa); (ii) loW doWn properties (sloW electrons doWn so that they can be boiling point; (iii) acceptably loW toxicity; (iv) chemical captured e?iciently at loWer energies and be prevented from inertness; (v) good thermal stability; (vi) non-?ammable; generating more electrons by electron impact ioniZation); and (vii) high cooling capability; (viii) good compatibility With (iii) have loW ioniZation cross section and high ioniZation 45 solid materials; (ix) good partial discharge characteristics; onset (prevent ioniZation by electron impact). Besides the (x) useable over a range of temperatures; and (xi) safe, easy above properties, there are a number of other basic properties to handle, inexpensive and securely available. Which are necessary for the complete characterization of the The present inventors have discovered a unique series of dielectric gas behavior and its performance in practice, e.g., dielectric gases for use in electric equipment applications, secondary processes such as electron emission from surfaces 50 Which exhibit many of the aforementioned properties, Which by and photon impact; photoprocesses; absorption of avoiding the greenhouse problems associated With SP6. Such photoioniZing radiation (this is a controlling factor in dis dielectric compounds exhibit at least one of the folloWing charge development in non-uniform ?elds); dissociation properties: under electron impact decomposition; ion-molecule reac A boiling point in the range betWeen about —200 C. to about tions; reactions With trace impurities; and reactions With sur 55 —2730 C. faces. LoW, preferably, Non-ozone depleting The dielectric gas must also have the folloWing chemical properties: high vapor pressure; high speci?c heat, high ther A GWP less than about 22,200 mal conductivity for gas cooling; thermal stability over long Chemical stability, as measured by a negative standard periods of time for temperatures greater than 4000 K.; chemi 60 enthalpy of formation (dHf<0) cal stability and inertness With regard to conducting and insu A toxicity level such that When the Working gas leaks from lating materials; non-?ammable; toxicity acceptable for equipment at the manufacturer’s speci?ed maximum industrial exposure; and non-explosive. When used in mix leak rate, the effective diluted concentration does not tures, it must have appropriate thermodynamic properties for exceeed its PEL, i.e., does not exceed the PEL of that mixture uniformity, composition, and separation. 65 speci?c compound. In general With minimal ventilation Extrinsic properties are those Which describe hoW a gas PELs greater than about 0.3 ppm by volume are accept may interact With its surroundings, or in response to external able (i.e., an Occupational Exposure Limit (OEL or

US 7,807,074 B2 29 30

TABLE 2-continued

Dielectric MY Compound Structure Nalne CAS MW BP(° C )

FNO Nitrosyl fluoride 7789-25-5 49.00 —59.9 FNO3 Fluorine nitrate 7789-26-6 81.00 —46.2 H28 H28 Hydrogen sul?de 7783-06-4 34.08 -59.5 H3N NH3 Ammonia 7664-41-7 17.03 -33.3 He He Helium 7440-59-7 4.00 -268.9 H1 H1 Hydrogen iodide 10034-85-2 127.91 -35.6 Kr Kr Krypton 7439-90-9 83.80 -153.4 N2 N2 Nitrogen 7727-37-9 28.01 -195.8 N20 NON Nitrous oxide 10024-97-2 44.01 -88.5 Ne Ne Neon 7440-01-9 20.18 -246.1 NO NO Nitrogen oxide 10102-43-9 30.01 -151.8 Xe Xe Xenon 7440-63-3 131.29 -108.1

The aforementioned dielectric compounds may be used in pure form, but can also be used as part of an aZeotrope, or a mixture With an appropriate second gas, i.e., nitrogen, CO2 or 20 N O Breakdown voltage at 2 ' . . . . Dielectric strength Pressure maximum pressure ~Partlcularly preferred non-electr1cal properties for d1elec- Gas kV/O_1 inch gap (psia) (kV/m inch gap) tr1c gases accord1ng to the present d1sclosure, 1nclude: Non-liquefying, e.g., Thol-Z less than —200 C. A“ 4-75 73-5 23-75 ~ ~ ~ R143a 5.8 73.5 29 Chem1cally stableidecompos1t1on temperature must be 25 R1523 5 9 73 5 29 5 higher than hot spot temperature in equipment, e.g., R125 6_4 735 32 Tdec:200o C., and gas should not decompose in partial R134a 6.6 73.5 33 discharge spark (approximately 10000 K) R22 7-2 73-5 39-9 LoW env1ronmental. 1mpact,. 1.e.,. l1ttle- to no destruct1on~ of R124SP6 10.414 0 55.573 5 39.370 oZone layer ODPIO; and loW global Warming impact 30 C318 16:0 45:3 493 GWP less than SP6 R115 16.0 73.6 80 Acceptably loW toxicity of gas and discharge byproducts R114 17-0 31-1 36 Electrical equipment property requirements for dielectric gases according to the present disclosure, include: Insulation speci?c criteria include a critical ?eld of B6,, and 35 EXAMPLE 2 no conducting decomposition products should be gen erated by discharge The dielectric strength of additional gases is measure at 1 SW1tch1ng spec1?c cr1ter1a1nclude h1gh cr1t1cal ?eld of B6,, atmosphere and at the maximum system pressure, Their arelng stablhty, 1e, 8 gas must reeOmblne IO onglnal breakdown Voltages are found to be greater then air, Which mOleeular SII'ueIUl‘e after belng decomposed 111 SWlIeh- 40 alloWs smaller gaps and therefore smaller equipment then lng are (GlbbS free energy OfreaeI10n1S<0) Would be need if air Was used. Here the measurements Were spec1?c thermal lntermptlon Performance, 1e, 1111151 be performed on CTFE (Chlorotri?uoroethylene), HCl (hydro able to 1nterrupt current ?oW at ac current Zero gen chloride) and SiF4 (silicon tetra?uoride), Arc 605101} PrOduCt from equlpmem and gas 11111511101 form Having described the invention in detail by reference to the Conducnon deposlts 45 preferred embodiments and speci?c examples thereof, it Will LOW Veloclty of Sound be apparent that modi?cations and Variations are possible Without departing from the spirit and scope of the disclosure EXAMPLE 1 and claims.

Measurements of the dielectric strength of potential alter- 50 What is Claimed 151 natives were determined using ASTM D2477 Or Obtained 1. An 1nsulat1on gas 1n electr1cal equ1pment, the 1nsulat1on from literature. These measurements were performed at 1 gas cons1st1ng of phosphorous penta?uorlde and at least one atmosphere pressure across a 0,1 ineh gap and at ambient gas selected from the group cons1st1ng of n1trogen, CO2, and temperature. N20. In the intended applications, the gas Will not be at 1 atmo- 55 2. The insulation-gas according to claim 1, Wherein said sphere pressure but at a higher pressure. In this example 5 electrical equipment is selected from the group consisting of atmospheres pressure is used as a maximum pressure. If the current-interruption equipment, gas-insulated transmission gas lique?es at a lower pressure than that pressure was used, lines, gas-insulated transformers, and gas-insulated substa These gases have higher dielectric strengths and break down tions. Voltages than air. Using 5 atmospheres (73.5 psia) pressure as 60 the upper pressure (rating of the equipment).