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Sulphur Hexafluoride Solvay Fluor und Derivate
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Page 1: Solvay - Sulphur Sf6

Sulphur Hexafluoride

SolvayFluor und Derivate

Page 2: Solvay - Sulphur Sf6

Solvay Fluor und Derivate GmbH

Contents

3 Sulphur Hexafluoride

SF6 – a gas with unusual properties 5

Areas of application for sulphur hexafluorideElectrical engineering 6

High-voltage switchgear and switching stations 7

SF6 for the Itaipú hydroelectric powerstation 10

Gas insulated transmission line (GIL) 11

Medium-voltage switchgear 12

High-voltage cables 13

Transformers 13

Other high-voltage applications 14

SF6 for the Vivitron accelerator 15

Manufacture of insulating glass 16

Foundry practise: magnesium 17

Foundry practise: aluminium 19

Other areas of application 20

Electrical propertiesElectron affinity 21

Dielectric constants 21

Dielectric strength 22

Arc-quenching capacity 24

Loss factor 24

Other physical propertiesMechanical and caloric data 26

Solubility 27

Specific heat 27

Vapour pressure 27

Mollier-h, lgp-Diagram for SF6 29

Pressure in the SF6 tank as a function of temperature and density 30

Optical properties 33

Chemical behaviourBehaviour at elevated temperatures 34

Behaviour under the influenceof electrical discharges 34

Corrosion characteristics of SF6and its decomposition products 34

Measures for the removal of corrosive constituents 35

ToxicityNew SF6 36

Contamined SF6 36

SF6 handling proceduresFilling an enclosed system 37

Temporary storage during service and maintenace 38

Handling of SF6 service equipment 38

Safety instructions 39

Specifications 41

Packaging for SF6according to IEC 376 42

The Responsible CareProgramme for SF6 44

Transport of used SF6 45

Life cycle assessment study 46

Product stewardship for SF6 48

Fluorine compoundsfrom Solvay Fluor 49

Your Solvay contact 49

Bibliography 50

Further publications about SF6 by Solvay Fluor 50

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Solvay Fluor und Derivate GmbH

4Sulphur Hexafluoride

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SF6 – a gas withunusual properties

5 Sulphur Hexafluoride

Solvay's sulphur hexafluoride is a non-tox-ic, inert, insulating and cooling gas of highdielectric strength and thermal stability.

It is particularly suitable for application inboth high-voltage and medium-high volt-age power circuit breakers as well as inhigh-voltage cables, transformers, trans-ducers, particle accelerators, X-ray and UHFequipment.

The construction of new equipment withhigher capacity and improved performancehas been made possible by the excellentelectrical, thermal and chemical propertiesof SF6. Changing from conventional die-lectrics to sulphur hexafluoride–a non-flammable, chemically-inactive and non-toxic heavy gas–results in considerablespace and weight savings and improves theoperational safety of converted equipment.

The low acoustic velocity is a feature whichmakes sulphur hexafluoride an excellentfilling for insulating-glass units.

SF6 gas mixtures improve sound-absorp-tion. In this way they contribute to the re-quirements of energy conservation and im-proved living conditions.

On account of their high reactivity, magne-sium and magnesium alloys must be pro-tected against reaction with atmosphericoxygen during casting. Even small quan-tities of sulphur hexafluoride added to theatmosphere above the melt provide thenecessary protective layer, making thismethod a very economical one.

A further new area of application in foun-dry practice is the purification of aluminiummelts. Introducing SF6/inert gas mixturesinto the liquid aluminium not only consid-erably reduces the hydrogen content butalso removes oxides and solid inclusions.

Even in the very lowest concentrations, sul-phur hexafluoride can be detected by hal-ogen leak detectors. SF6 is therefore usefulas an additive to other gases as a tracer forthe purposes of leak detection, or it can beused as a constituent of air for meteorolog-ical measurements.

SF6 is also widely used in medical technolo-gy. For example as a contrast agent in ultra-sonic examinations as well as in ophthal-mology, pneumonectomy and diseases ofthe middle ear, e.g. treating loss of hearingin middle ear infections [1].

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Solvay Fluor und Derivate GmbH

Areas of application for sulphur hexafluoride

6Sulphur Hexafluoride

Electrical engineeringThe use of sulphur hexafluoride in place ofsolid and liquid insulators offers a number ofimportant advantages:

● High dielectric strength ● at lower cost

When pressurized, sulphur hexafluoride canexhibit the same dielectric strength as liquidinsulators. However, the per-unit-volumecost of SF6 is only a fraction of that of liquiddielectrics.

● Regeneration capacity

Following a breakdown, sulphur hexafluo-ride regenerates itself. Its original strength isspontaneously restored and, in most cases,is even slightly enhanced.

● Low pressure-increase in ● the case of breakdown

Due to the very low adiabatic coefficient ofsulphur hexafluoride, the pressure rise as aresult of thermal expansion following dielec-tric breakdowns is less than that with othergases and very considerably less than is thecase with liquid dielectrics.

fig. 1 Enclosed, SF6-insulated,high-voltage plant (ABB, Switzerland)

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7 Sulphur Hexafluoride

fig. 2 SF6-insulatedhigh-voltage switching station type L-SEP, 145 kV(VA Tech Elin Holec High Voltage, Netherlands)

fig. 3 Gas insulated, high-voltage switching station for 145 kV operating voltage(Siemens, Germany)

High-voltage switchgearand switching stationsThe excellent quenching and insulatingproperties of sulphur hexafluoride have per-mitted the construction of completely newtypes of high-voltage circuit breakers andswitching stations with outstanding fea-tures: compact and space-saving design,low noise-levels, protection against acciden-tal contact of live parts, against intrusion offoreign matter through the metal claddingand elimination of the fire hazard.

Substations using sulphur hexafluoride forinsulation purposes are particularly in de-mand where, on account of limited space, acompact design is required. These substa-tions occupy only 10-15% of the space re-quired by conventional units. New SF6-filledequipment can thus be installed at distribu-tion points in densely-populated areaswhere site costs would prohibit the use oftraditional methods.

Thanks to their insensitivity to polluted air,enclosed outdoor versions of SF6-insulatedsubstations are installed in the chemical in-dustry, in desert regions and in coastal areas.

SF6 is used as a quenching agent both inpower circuit breakers for enclosed substa-tions and in circuit breakers for open out-door substations.

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8Sulphur Hexafluoride

fig. 4 Enclosed switching station, 500 kV(Alstom, France)

fig. 5 Gas insulated High-voltage switching station,550 kV(Siemens, Germany)

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9 Sulphur Hexafluoride

fig. 7 SF6 switching station, 245 kV(Schneider Electric High Voltage, France)

fig. 6 Outdoor transforming station with SF6 equipment,420 kV(Siemens, Germany)

fig. 8 High-voltage switching station,170 – 245 kV,(Alstom, Switzerland)

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10Sulphur Hexafluoride

SF6 for the Itaipúhydroelectric stationSolvay Fluor und Derivate GmbH suppliedthe SF6 for the world's largest hydroelectricpower station at Itaipú in Brazil. The out-put at Itaipú is particularly impressive: 18turbines supply 12.6 billion watts, equiva-lent to the output of 10 nuclear power sta-tions. The largest SF6-insulated high-volt-age switching station in the world was in-stalled at Itaipú, and contains more than100 tons of sulphur hexafluoride.

fig. 9a Hydroelectric power station Itaipú, Brazil

fig. 9b 550 kV SF6-insulatedhigh-voltage switching station for the Itaipú hydroelectric power station in Brazil (ABB, Switzerland)

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11 Sulphur Hexafluoride

Gas insulated transmission line (GIL)

Gas insulated transmission lines are partic-ularly well suited for high power transmis-sion. Conventional designs are filled withpure SF6, and have been operating safelyand reliably in all parts of the world formore than 20 years.

The advantage of this technology is thehigher capacity compared with cables.

GIL’s are either buried or laid in tunnels.They are a viable alternative for energy sup-ply where overhead power lines are eithernot possible or where the capacity of cablesis insufficient.

For long distances the replacement of pureSF6 with more economical SF6/N2 mixtureshas been researched because the arc extin-guishing properties of SF6 are not relevantin insulating applications.

Today the overall optimisation of gas mix-tures, gas pressure and dimensions of GILmean this technology is a highly competi-tive transmission medium in a broad rangeof applications.

Solvay Fluor und Derivate GmbH TechnicalService supports this new application with aspectrum of services ranging from the initialproduction of mixtures through to the sep-aration of mixtures at end of service life orwhenever required. By offering this techni-cal support Solvay enables a closed productloop for SF6/N2 mixtures.

fig. 10 SF6/N2 mixture in transmission lines, in tunnel (Siemens, Germany)

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12Sulphur Hexafluoride

Medium-voltageswitchgearThe advantages of SF6 technology, in par-ticular its excellent arc-quenching capacity,are also put to good use in circuit breakersfor the 10-40 kV range. They replace con-ventional, low-oil-volume circuit breakersand also satisfy heavy-duty requirementssuch as those occurring under short-circuitconditions and repeated switch-off underload.

Like the high-voltage circuit breakers, theyrequire little maintenance and are particu-larly suitable for locations where oil-filledequipment is undesirable.

fig. 12 Metal-clad SF6-insulated switching station in a compact design (ABB Calor Emag, Germany)

fig. 11 Medium-voltage, heavy-duty power circuit breakers of the Minex type. SF6-insulated for installation in local-network and consumer stations(Driescher, Germany)

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13 Sulphur Hexafluoride

In high-frequency carrier sytems, outputhas been increased almost tenfold throughthe use of SF6-filled tubular transmissionlines. An advantage from the construction-al point of view is the ability to build high-performance UHF transmission stationswith greatly reduced dimensions.

TransformersIts excellent heat-transfer capacity, non-flammability and non-toxicity have alsopromoted the use of sulphur hexafluoridein the construction of transformers.

On account of their high operational safe-ty, SF6-gas transformers are installed inmines and department stores. Their relati-vely light weight, compact design and lownoise levels are decisive advantages.

fig. 14 SF6-insulated high-voltage cable in the JET nuclear-fusion plant (kabelmetal electro, Germany)

fig. 13 SF6-insulatedtransformer,23–107 kV (Fuji, Japan)

High-voltage cables and tubular transmission linesIn recent times, increasing interest hasbeen shown in the application of sulphurhexafluoride in the manufacture of gas-in-sulated high-voltage cables and tubulartransmission lines used for high-power dis-tribution in heavily concentrated industrialareas.

Tubular transmission lines are also used toconnect power stations with transformersor switching stations, as for example in thecase of underground power stations. Ap-propriately-dimensioned tubular transmis-sion lines filled with pressurized SF6 permitunusually high current levels. Compared tothose values achieved with conventionaltypes of cables, figures for charging-cur-rent and dielectric loss are insignificant.

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14Sulphur Hexafluoride

Other high-voltage applicationsThe use of sulphur hexafluoride has also es-tablished itself in the insulation of super-voltage generators in particle-acceleratingmachines, such as in Van de Graaf acceler-ators, betatrons, neutron generators andother such plant used for radiation applica-tions in scientific institutions, medicine andindustry.

By virtue of the high dielectric strength ofthe gas, pressure vessels can be construct-ed in considerably lighter fashion. The useof SF6 in older units, previously insulated

with mixtures of air and carbon dioxide,has resulted in a marked increase in effi-ciency.

SF6 fulfills a similar function in voltage sta-bilizers for electron microscopes and in X-ray equipment used in production controland the non-destructive testing of materi-als.

Parallel to the development of SF6 planttechnology in the high-voltage sector, SF6-insulated, high-voltage measuring instru-ments and calibrated power sources havealso been produced. SF6-fillings are alsoused in instrument transformers, pressur-ized gas capacitors and surge arresters forsuper voltages.

fig. 15 525 kV SF6 instrument transformer(Alstom, Belgium)

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15 Sulphur Hexafluoride

SF6 for the Vivitron acceleratorThe largest electrostatic accelerator in theworld is already in operation in Strasbourg.

Using new technology, the Tandem Van deGraaf Vivitron accelerator is designed toachieve an accelerating potential of 35 mil-

lion volts. It is 51 m long, has a maximumdiameter of 8.5 m and a volume of 1200m3. The SF6-gas supply is contained in twostorage tanks whose total SF6-capacity is60 tonnes. Solvay Fluor und DerivateGmbH was responsible for both the supplyof SF6 and the associated logistics for thisproject.

fig. 16 Perspective view of the Vivitron accelerator and the SF6-gas supply system with its two SF6 storage tanks (Centre de recherches nucléaires, France)

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16Sulphur Hexafluoride

Manufacture of insulating glassSulphur hexafluoride is being used in incre-asing quantities in the construction of insu-lating-glass building components. The re-quirements of energy conservation and im-mission protection have greatly increasedthe demands made on such units. In windowmanufacture, substantial progress has beenmade in the field of thermal insulation byusing three-pane units and by coating two-pane units with metals or metal oxides. Fil-ling the spaces between panes with SF6 re-sults in yet further improvements.

The improvement of sound insulation byenlarging the spaces between the windowpanes and the use of thicker glass usuallycalls for a change in window-frame design.In the case of conventional two-pane glass,infilling with SF6 produces improvements

of up to 8 dB, depending upon shapes andmaterials used.

Since sulphur hexafluoride is chemically in-ert, there is no risk of its reacting with glass,metal or sealing compounds. Its coefficientof permeability is extremely low.

Solvay SF6 has a very high purity, and itsdew-point, which is guaranteed to be be-low –40 °C, is usually around –50 °C. In or-der to keep the dew-point as low as possi-ble, molecular sieves, preferably size 3A butnot greater than 4A, must be used.

To fill an insulating-glass unit, the air is dis-placed slowly from the bottom upwards bythe much heavier SF6-gas (whose density isapproximately 5 times greater). The gas isdosed with the aid of either simple flowmeters or using automatic filling devices,depending on the production quantities in-volved.

fig. 17 SF6-filled insulating-glass panes

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17 Sulphur Hexafluoride

Foundry practice: magnesiumMagnesium is a highly reactive metal. Itmust therefore be protected during thecasting process, when temperatures of upto 800 °C can occur, against ignition, oxi-dation and the formation of nitrides. Up tonow, only molten salts and SO2 or pow-dered sulphur were known as protectivematerials for this purpose. Although theyprovide adequate protection, such materi-als have detrimental secondary effects,such as corrosion, generation of bad smellsand the contamination of the cast compo-nents by salt. The use of SF6 as a protectivegas eliminates these disadvantages.

In contrast to pure argon, for instance, SF6prevents the evaporation of magnesium byforming a thin protective layer. Only verylow concentrations of SF6 are necessary ab-ove the melt to achieve this effect, assu-ming that the melting pot is tightly sealedand that the opening for topping up is keptas small as possible and closed by means ofa sliding gate. Accordingly, opening peri-ods should be kept as short as is practica-ble.

Sulphur hexafluoride is always used in con-junction with a carrier gas, as this achievesa faster and more effective distributionacross the melt on account of the larger to-tal quantity of gas. Air, carbon dioxide, ar-gon and nitrogen are all suitable for use ascarrier gases. In foundry practice, the resid-ual nitrogen from empty refill cylindersfrom die-casting machines is used for thispurpose.

fig. 18 Schematic representation of a protective-gas supply system for a magnesium melting furnace

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18Sulphur Hexafluoride

Optimum dosage and concentration of theprotective gas depend upon such factors asfurnace design and levels of pig feedingand molten-charge removal, and must bedetermined by trial and error. As a rule asuitable mixture consists of 0.04 – 0.3 vol. %SF6 and more than 99 vol. % of an air/CO2mixture and is distributed evenly over thesurface of the melt [2].

As only a very thin protective film should beformed and waste metal should be kept toa minimum, an initial value of 100 l of gasmixture per hour is generally used. Thedosage can be decreased or increased insteps, as required.

Once metal has ignited, the resulting firecannot be extinguished even with highconcentrations of SF6.

Flow meters are used for both mixing anddosing the gases (manufacturers will benamed on request).

Since only small amounts of SF6 are used,no problems arise with decompositionproducts. Measurements taken in the im-mediate vicinity of the melting plant showreadings well below the TL value of HF = 3 ppm (2 mg/m3). SF6 is therefore anideal protective gas for magnesium meltsfrom the point of view of both operationalsafety and environmental considerations [3].

fig. 19 Furnace magnesium-moulding plant, using SF6-CO2-air as a protective gas. Made by Huskvarna AB, Sweden (Norsk Hydro, Norway)

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19 Sulphur Hexafluoride

Foundry practice: aluminiumA fundamental problem in the productionof aluminium cast components is porositycaused by the hydrogen content of the alu-minium melt. The porosity induced by thepresence of hydrogen leads to a reductionin strength of the components. Such an ef-fect can only be avoided by pre-treating thealuminium melt.

Until now, the treatment carried out for pu-rifying the aluminium melt had several dis-advantages. The most widely used purify-ing method is the introduction of chlorineor mixtures of chlorine and inert gas. Ho-wever, the aggressivity of elemental chlori-ne means that special safety precautionsare necessary in handling. And the intro-duction of pure inert gases such as argonreduces the hydrogen content but leads toother difficulties on account of the removalof the alkaline and alkaline-earth metalsand solids.

The use of hexachloroethane in powder ortablet form also leads to problems, since,when it is used, chlorine is released. Theuse of fluorohydrocarbon purificationmethods will be terminated entirely in thefuture on account of their potential influ-ence on the ozone layer.

The product sulphur hexafluoride opens upa completely new purification technique tothe aluminium industry for aluminiummelts. The introduction of SF6/inert-gasmixtures into the liquid aluminium signifi-cantly decreases the hydrogen content andat the same time leads to the removal ofoxides and solid contaminants. HandlingSF6 gas mixtures presents no problems andSF6 is generally recognized as physiologi-cally safe. The introduction of SF6 therefo-re not only enhances product quality but al-so improves working conditions.

fig. 20 SF6-treated and untreated aluminum cast pieces in section

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20Sulphur Hexafluoride

Other areas of applicationEven at the lowest concentration levels,sulphur hexafluoride is detected by modernhalogen leak detectors.

For this reason it is used increasingly as atest gas for detecting leaks in boilers, fueltanks, pneumatic devices, pipeline systems,plastic tubing, containers for carrying ra-dioactive materials and many other vessels.By carrying out a calibrated leak, quantita-tive measurements are also possible. Withthe increasing demands imposed by everstricter standards of environmental protec-tion, work safety and energy saving, thistechnique is gaining steadily in significance.

Residence-time distributions in high-veloci-ty-flow assemblies can be determined us-ing SF6. This method is primarily applied inthose cases where a radiometric methodcannot be employed [4].

On account of its very low detection limit,SF6 is used as a tracer gas for meteorolog-ical measurements. When added in mea-sured quantities at an emission source, thedistribution of the emitted substances canbe determined even at relatively long dis-tances. Its high stability and the low solubil-ity of SF6 in water are of particular advan-tage in this respect.

SF6 is also widely used in medical technolo-gy. For example as a contrast agent in ultra-sonic examinations as well as in ophthal-mology, pneumonectomy and diseases ofthe middle ear, e.g. treating loss of hearingin middle ear infections [1].

fig. 21 Ophthalmology

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21 Sulphur Hexafluoride

Electrical properties

Electron affinityThe excellent insulating properties of sul-phur hexafluoride are attributable to thestrong electron affinity (electronegativity)of the SF6 molecule. This is based mainlyon two mechanisms, resonance captureand dissociative attachment of electrons, inaccordance with the equations:

SF6 + e– —> SF6– (1)

SF6 + e– —> SF5– + F (2)

The process represented by equation (1)applies to electron energies of 0.1 eV withan energy range of 0.05 eV, and that re-presented by equation (2) applies to anenergy range of 0.1 eV [5].

Dielectric constantsThe dielectric constant has a value of1.0021 at 20°C, 1.0133 bar and 23.340MHz; a rise in pressure to 20 bar leads to anincrease of about 6 % in this value.

At -50 °C, the dielectric constant of liquidsulphur hexafluoride throughout the rangefrom 10 to 500 kHz remains unchanged at1.81 ± 0.02 [6].

fig. 22 50 Hz breakdown voltage of SF6 in a homogeneous field as a function of the distance between electrodes at various gas pressures (ETZ Supplement 3 [1966])

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22Sulphur Hexafluoride

fig. 23 Relation of breakdown voltage to pressure (IEEE Trans. Pow. App. Syst. 66 [1963] 357) Comparison SF6 andN2/CO2-mixtures

Dielectric strengthThe strong interaction of high-energy elec-trons with the polyatomic SF6 moleculecauses their rapid deceleration to the lowerenergy of electron capture and dissociativeattachment. SF6-breakdown is thereforeonly possible at relatively high field strengths.

The breakdown voltages at 50 Hz and 1bar in a homogenous field are thus 2.5 to3 times higher than the corresponding val-ues for air or nitrogen (fig. 22).

Figure 23 shows the relationship of break-down voltage to pressure in a non-homo-geneous field in comparison with that of aN2/CO2 mixture.

The breakdown strength of air is dramati-cally increased by the addition of smallquantities of SF6. In contrast, air has only alimited influence on the breakdownstrength of sulphur hexafluoride. The addi-

tion of 10 % of air by volume reduces thebreakdown voltage of SF6 by about 3 %,the addition of 30 % air by about 10 %.

The breakdown voltage of SF6 reaches thatof transformer oil at a pressure of only 3bar (fig. 24).

The behaviour of sulphur hexafluoride con-forms over a wide range of pressures to Pa-schen's Law: at higher pressures, however,deviations have been observed under cer-tain conditions [7, 8, 9 ].

The breakdown strength of SF6 is indepen-dent of frequency: it is therefore an idealinsulating gas for UHF equipment [10].

The Corona-onset voltage using SF6 innon-homogeneous fields is also consider-ably higher than that using air. Figures 25and 26 show the respective dependenceon pressure and radius of curvature of theelectrodes in the case of SF6 and air in apoint-to-plane electrode system.

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23 Sulphur Hexafluoride

fig. 24 Breakdown strength of transformer oil, air and SF6 as a function of gas pressure(Kali und Steinsalz, 3, issue 10 [1963] 319)

fig. 25 Dependence on pressure of the Corona-onset voltage in SF6 and air (ETZ, Supplement 3 [1966] )

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24Sulphur Hexafluoride

fig. 26 Corona-onset voltages for SF6 andair as a function of the radius of curvature rK at atmospheric pressure (ETZ, Supplement 3, [1966])

Arc-quenching capacityOn account of its thermal properties andlow ionisation temperature, sulphur hexa-fluoride exhibits outstanding characteristicsfor the extinguishing of electric arcs (fig.27).

All other conditions being equal, the arc-quenching time using SF6 is about 100times less than that using air [11].

The superior arc-quenching performanceof SF6 compared with other gases is im-pressively illustrated in figure 28.

Loss factorThe loss factor, tan ∂ of sulphur hex-afluoride is extremely low (less than 2.0 ·10-7).A value of tan ∂ < 10-3 was determined forliquid SF6 at –50 °C [6].

Diagrams and data pertinent to the elec-trical properties of sulphur hexafluoridemay be found in the Milek "Sulphur hex-afluoride data sheets" [12].

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25 Sulphur Hexafluoride

fig. 27 Radial temperature profile in SF6 and N2 electric arcs(schematic representation: from Z. Angew. Physik 12, [1960] 5, pp 231 to 237)

fig. 28 Quenching capacity of SF6, air and a mixture of both gases (Insulating Materials for Design and Engineering Practice, N.Y. [1962], p. 116)

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Other physicalproperties

Sublimation point ( 1.0133 bar ) –63.9 °C

Melting point ( 2.26 bar ) –50.8 °C

Vapour pressure see page 27

Heat of sublimation 153.2 kJ/kg

Heat of fusion 34.37 kJ/kg

Heat of vaporization [13]:

Temperature (°C ) –20 0 +20 +40

Heat of vaporization ( kJ/kg ) 91.71 78.96 62.54 34.08

Critical data [13]:

Critical temperature 45.58°C

Critical pressure 37.59 bar

Critical density 0.74 kg/l

Density: ( see figs. 29 and 31)

Gas density ( 20 °C, 1 bar ) 6.07 g/l

Liquid density ( 0 °C, 12.65 bar) 1.56 kg/l

Solid density (–100 °C) [14] 2.77 kg/l

Viscosity ( see fig. 32)

Thermal conductivity ( see fig. 33)

Heat transfer capacity ( see fig. 34)

Acoustic velocity in SF6

( 0 °C, 1.0 bar ) 129.06 m/sec.

Isentropic exponent ( K ) [13]:

The dynamic compressibility of

SF6 is particularly high on account

of the low value of the isentropic

exponent: K = 1.08 ( 30 °C, 1.0 bar )

Heat of formation ( ∆ HB, 25 °C )* –1221.58 ± 1.0 kJ/mol

Entropy of reaction ( ∆ SB, 25 °C )* – 349.01 J/mol k

* for formation from rhombic sulphur and gaseous fluorine [14].

Sulphur hexafluoride is a colourless, odour-less, non-toxic and non-flammable gas.With a molecular weight of 146.05, SF6 isabout 5 times heavier than air and one ofthe heaviest known gases.

Mechanical and caloric data

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27 Sulphur Hexafluoride

Vapour pressure(cf. fig. 29)

Temperature (°C) –50 – 45 – 40 – 35 –30 – 25 – 20 –15 –10 –5

Pressure (bar) 2.34 2.87 3.49 4.20 5.02 5.95 7.01 8.19 9.52 11.01

Temperature (°C) 0 +5 +10 +15 +20 +25 +30 +35 +40 +45

Pressure (bar) 12.65 14.47 16.47 18.67 21.08 23.72 26.62 29.79 33.27 37.13

Solubility

Solubility in water [15]

Gas volume corrected

to 0 °C, 1.0133 bar

Temperature (°C) 5 10 15 20 25 30 40 50

Solubility (cm3 SF6/kg H2O) 11.39 9.11 7.48 6.31 5.44 4.79 3.96 3.52

Solubility intransformer oil [16]

(Esso-Univolt 35)

Gas volume under 0 °C, 1.0133 bar

Temperature (°C) 27 50 70

Solubility (cm3 SF6/cm3 oil) 0.408 0.344 0.302

Specific heat (Cp)

Solid and liquid phase [17]

Temperature (K) 200 210 220 225 230

Specific heat (J/mol K) 104.17 116.60 184.22 110.95 119.58

Gas phase (1 bar) [14, 18]

Temperature (K) 298 373 400 473 500 573 600 673 700 773 1273

Specific heat (J/mol K) 97.26 112.45 116.39 125.89 128.54 134.51 136.07 140.21 141.1 144.35 152.62

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28Sulphur Hexafluoride

fig. 29 Vapour pressure curve:lines of equivalent gas density of SF6

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29 Sulphur Hexafluoride

fig. 30 Mollier-h, Igp diagram for sulphur hexafluoride

Mollier-h, Iog p-diagrammefor sulphur hexafluorideSF6

Established by Dr.-Ing. R. Döring

Units: p in bar, h in kJ/kg, s in kJ/kg K,v in m3/kg, s=1 kJ K, h=200 kJ/kg at 0 °C for the boiling liquid

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30Sulphur Hexafluoride

Internal pressure in SF6 tankas a function of temperature and Calculated from experimental values [13]density (kg SF6/ l tank volume)

Pressure in bar

Densitykg/l 5 °C 10 °C 15 °C 20 °C 25 °C 30 °C 35 °C 40 °C 45 °C 50 °C 55 °C 60 °C 65 °C 70 °C

0.940 43.1 49.3 55.5 61.8 68.3

0.960 43.6 50.1 56.5 63.1 69.6

0.980 44.2 50.9 57.7 64.3 71.2

1.000 44.8 51.8 58.8 65.8 73.0

1.020 45.6 52.9 60.1 67.4 74.8

1.040 46.4 54.0 61.1 69.2 77.0

1.060 47.4 55.3 63.3 71.3 79.4

1.080 48.4 56.7 65.0 73.7 82.1

1.200 49.8 58.5 67.3 76.2 85.2

1.120 33.7 42.5 51.3 60.3 69.5 78.9 88.5

1.140 34.9 44.1 53.3 62.7 72.4 82.2 92.1

1.160 36.5 46.0 55.5 65.5 75.5 85.6 96.1

1.180 38.0 48.1 58.2 68.5 79.0 89.7 100.6

1.200 40.1 50.7 61.3 72.2 83.2 94.3 105.6

1.220 42.6 53.7 64.8 76.2 87.7 99.5 111.3

1.240 45.3 57.1 68.8 80.7 92.8 105.3 117.6

1.260 48.6 61.0 73.5 85.9 98.6 111.7 124.4

1.280 27.0 39.7 52.5 65.6 78.7 91.9 105.0 118.9 132.2

1.300 30.3 43.7 57.1 70.9 84.6 98.4 112.2 126.4 140.5

1.320 34.3 48.3 62.4 76.8 91.2 105.7 120.2 134.9 149.9

1.340 38.8 53.7 68.5 83.5 98.6 113.7 129.0 144.4 159.8

1.360 43.9 59.6 75.3 90.9 106.5 122.6 138.8 154.6 170.8

1.380 49.9 66.4 82.9 99.2 115.6 132.5 149.5 166.0 183.0

1.400 24.0 40.5 56.9 74.0 91.4 108.5 125.8 143.6 161.4 178.9 196.5

1.420 30.7 47.9 65.0 83.1 101.3 119.2 137.2 155.8 174.6 193.2 (211.8)

1.440 20.9 38.2 56.2 74.5 93.5 112.4 131.3 150.2 169.4 189.0 (209.2) (229.5)

1.460 27.9 46.8 66.0 85.4 105.2 125.0 144.9 164.9 185.0 (205.4) (226.7)

1.480 16.4 36.5 56.7 77.1 97.6 118.2 139.1 160.2 181.4 (202.5) (223.6)

1.500 25.4 46.8 68.1 89.5 111.1 132.7 154.6 176.8 (199.1)

1.520 (14.8) 36.8 59.0 81.3 103.8 126.4 149.2 172.1 (195.3) (218.4)

1.540 (27.5) 50.4 73.5 96.7 120.1 143.8 167.7 191.6 (215.6) (239.5)

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31 Sulphur Hexafluoride

fig. 31 Pressure/temperature curves for SF6(from Z. Phys. Chem., New Series 23 [1960] 96).(1at=0.9800665 bar)

fig. 32 Viscosity of SF6 as a function of temperature at atmospheric pressure [14]

0 °C 25 °C0.0141 0.0153

100 °C 200 °C0.0186 0.0228

300 °C 400 °C0.0266 0.0302

500 °C0.0335

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32Sulphur Hexafluoride

fig. 33 Thermal conductivity of SF6at atmospheric pressure [14]

fig. 34 Heat-transfer coefficients of air and SF6 (for comparison – transformer oil under natural convection)(Conti-Elektro-Berichte,July/September 1966, p 189)

0 °C 25 °C1.0 1.3

100 °C 200 °C1.9 2.5

300 °C 400 °C3.1 3.6

500 °C4.1

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33 Sulphur Hexafluoride

Optical properties

Refractive index [19] nD (0 °C) 1.0133 bar 1.000 783

fig. 35 Infrared spectrum of SF6 recordedfor three different concentrations(Leitz M 3, NaCl prism)

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34Sulphur Hexafluoride

Chemical behaviour

Under normal conditions, sulphur hexaflu-oride is chemically inert and stable; its reac-tivity is among the lowest of all substances.

Behaviour at elevated temperaturesSF6 can be heated to 500 °C in quartz con-tainers without any decomposition occur-ring. At temperatures of up to approxi-mately 150 °C, generally used materialssuch as metals, ceramics, glass, rubber andcast resins are completely stable in thepresence of sulphur hexafluoride. Not untilthe temperature exceeds 200°C do somemetals begin to have a decomposing effecton SF6; however, the usual working metalsand alloys do not have a significant decom-posing effect until the temperature reach-es 400 to 600 °C.

Since SF6 reacts with metals at high tem-peratures, it is used as a protective gas formelts. In particular, it is used in magnesiumfoundries because it forms a thin and im-pervious layer on the surface of the moltenmagnesium. This layer acts very effectivelyin preventing further reaction with air [20,3]. In spite of the high temperature of themolten magnesium alloys, there is only aminimal level of decomposition of the SF6.

Behaviour under theinfluence of electrical discharges [21]Electrical discharges cause a decompositionof the gas to an extent proportional to theconverted energy. Under the influence ofan electric arc, part of the sulphur hexaflu-oride is dissociated into its atomic constitu-ents, as shown in the following equation:

SF6 S + 6F

This reaction is reversible. After the dis-charge, the dissociation products recom-bine, provided that no secondary reactionswith vaporized electrode metal, the con-tainer wall or other constructional compo-nents occur.

Both solid and gaseous products can resultfrom these secondary reactions:

● metal fluorides, metal sulphides and ● metal oxides

● sulphur fluorides such as SF4

● sulphur oxyfluorides such as● SOF2, SO2F2, SOF4

Such decomposition products resultingfrom high-energy discharges are also gooddielectrics, so that dust-like deposits on thesurface of insulators do not impair the op-erational efficiency of affected equipment.

However, this applies only if the humidityin the gas chamber is very low. If exposedto moisture, the above-mentioned decom-position products hydrolyse and form sec-ondary products, for example as illustratedin the following equations:

CuF2 + H2O CuO + 2HF

SF4 + H2O SOF2 + 2HF

The hydrogen fluoride (HF) formed in thesereactions vigorously attacks any materialscontaining silicon dioxide (SiO2) (e.g. glassand porcelain). The use of these materialsin equipment in which SF6 is to be used forarc-quenching is therefore only suitable un-der certain special conditions.

Corrosion characteristics of SF6 and its decompo-sition productsAs already indicated, pure SF6 is chemicallyinert: it cannot, therefore, cause corrosion.

In the presence of moisture, however, theprimary and secondary decompositionproducts of sulphur hexafluoride form cor-rosive electrolytes which may cause dam-age and operational failure, particularly inelectrical equipment. If the formation ofdecomposition products cannot be avoid-ed by the use of appropriate constructionmethods, corrosion can be largely eliminat-ed by the careful exclusion of moisture andthe employment of suitable materials.

Commonly used metals such as aluminium,steel, copper and brass remain virtually freeof attack. In contrast, materials such asglass, porcelain, insulating paper and simi-lar materials may be severely damaged, de-pending on the concentration of the corro-sive substances. Insulating materials suchas epoxy-resin, PTFE, polyethylene, polyvi-nyl chloride and polymethylene oxide areeither only slightly or undetectably affected[22].

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35 Sulphur Hexafluoride

Measures for the removal of corrosiveconstituentsBoth moisture and the decomposition prod-ucts of sulphur hexafluoride can be relative-ly easily removed by adsorption. Aluminiumoxide and molecular sieves or mixtures ofthese materials are all suitable for this pur-pose. They very effectively and practically ir-reversibly adsorb the acidic and gaseousproducts. At the same time they also ensuremaintaining a low dew-point in the gas filling.

Especially suitable are adsorbing agents inthe form of filter fillings, through which thegas is pumped in a circulation. This methodis employed for example in the case of SF6power circuit breakers, where considerableconcentrations of decomposition productscan occur in arc quenching. In many cases,however, static filters provide adequate pro-tection.

Figure 36 shows the dew-point as a func-tion of the gas moisture content.

fig. 36 Dew-point as a function ofthe moisture content of SF6

dew-point in °C moisture contentin ppm by weight

–75 0.148–70 0.32–65 0.65–64 0.75–63 0.86–62 1.0–61 1.15–60 1.3–59 1.5–58 1.7–57 2.0–56 2.2–55 2.5–54 2.9–53 3.3–52 3.6–51 4.2–50 4.8–49 5.4–48 6.1–47 6.9–46 7.8–45 8.7–44 10.0–43 11.0–42 12.0–41 14.0–40 16.0–39 17.0–38 20.0

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36Sulphur Hexafluoride

Toxicity

New SF6Pure sulphur hexafluoride is absolutelynon-toxic. The by-products arising duringproduction of the gas are completely re-moved during subsequent purification op-erations.

Solvay sulphur hexafluoride is constantlytested for the presence of toxic constitu-ents using the inhalation test described inIEC Recommendation 376 (corresponds toDIN IEC 376, April 1980 and VDE 0373 Part1/4.80).

In places where work involving large quan-tities of sulphur hexafluoride in containersand in enclosed areas is carried out, thesafety regulations should take into accountthe potential asphyxiation hazard arisingfrom oxygen deficiency, as, due to its highdensity, the gas can displace air from low-er-lying regions of enclosed areas (pits,sumps etc). This hazard can, however, beeasily countered by the provision of ade-quate ventilation. Measuring instrumentsfunctioning on the principles of thermalconductivity can be installed to check theSF6 content of air.

The existing TLV in the Federal Republic ofGermany for sulphur hexafluoride is 6000mg/m3 = 1000 ppm.

Contaminated SF6It should be noted that electrical discharg-es (e.g. switching processes, fault electricarcs) lead to the formation of gaseous de-composition products and dusty metalcompounds. Gaseous decomposition prod-ucts of SF6 exhibit very characteristic warn-ing signs even at low concentrations. Thesewarning signs are for example pungent orunpleasant odours (like “rotten eggs”), orirritation of nose, mouth and eyes. Such ir-ritation occurs within seconds, well in ad-vance of any danger arising from poison-ing.

When handling contaminated SF6 caremust be taken not to breathe in gaseousor dusty decomposition products. In casethis cannot be achieved by technical safetymeasures, i.e. ventilation, personal protec-tive equipment must be worn. Personalprotective equipment consists of items ofprotection for the eyes, body and breath-ing. More detailed information on handlingSF6 is given in the information leaflet “SF6plant” (Trade Association for Precision Me-chanics and Electrical Engineering) and inthe DIN Standard IEC 480 and VDE 0373,Part 2/4.80.

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37 Sulphur Hexafluoride

SF6 handling procedures

SF6 can be removed from its pressurizedgas containers either in the gaseous or inthe liquid phase. During the removal of SF6in the gaseous phase, the pressure-regula-tor can be connected directly to the cylin-der valve. If the SF6 is removed in the liquid phase, then a vaporizer must be in-stalled between the container and the reg-ulator.

Filling an enclosed systemNormally, equipment is first evacuated andthen filled with SF6 under pressure. In thisprocess, the feed line from the gas cylinderto the unit to be filled is provided with abranch line incorporating a shut-off valve.This branch line leads to a vacuum pump.Before filling with SF6 commences, thecomplete system up to the cylinder valve isevacuated. After the valve in the branchline has been closed, both the cylinder andthe regulator are gradually opened.

It is advisable to observe the progress of theentire filling operation on an appropriatepressure gauge (centre-zero). The finalpressure of the gas in the filled unit will de-pend upon temperature. On account of thefact that

the gas undergoes a cooling process onleaving the steel cylinder, the pressure read-ing immediately following the completionof the filling operation will be less than thatshown after the gas temperature has risento the ambient level. This subsequent risein pressure must be taken into account.

fig. 36 Leak testing of a GIS aluminium housing (ABB, Switzerland)

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38Sulphur Hexafluoride

Temporary storage during service and maintenanceTemporary storage of SF6 during serviceand maintenance is highly recommendedin regard to SF6 reuse and as a preventivemeasure for environmental protection.

For the gas operations occuring duringtemporary storage so called service equip-ment should be available.

Handling of SF6 serviceequipmentThis kind of equipment consists of maincomponents such as SF6 compressor, vac-cuum pump, storage tank, evaporator andfilter unit, which are piped together withvalves and fittings. According to the size ofthe switch gear the appropriate equipmentwith sufficient storage capacity and perfor-mance is selected. SF6 gas handling in suchequipment is only carried out in closed cy-cles.

Every component within this cycle (SF6compressors and diaphragm compressors)are dry-running and therefore absolutelyoil-free without a chance of SF6 gas con-tamination. The built-in filters provide forthe drying and cleaning of the SF6 gas dur-ing each gas operation. SF6 valves, cou-plings and fittings guarantee a high degreeof leak-tightness and operational safety.

The connecting couplings should be self-closing in order to avoid air and moisturepenetrating into the lines.

When selecting service equipment, han-dling should be as easy as possible to avoidunnecessary faults. Maintenance equip-ment with automatic sequences is thestate-of-the-art and is preferred because ofits high degree of operational safety.

fig. 38a SF6 measuring devices (DILO, Germany)

fig. 38b SF6 servicing unit (DILO, Germany)

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39 Sulphur Hexafluoride

Safety instructions

Contaminated SF6If SF6 does not contain any hazardoussubstances its potential hazards are com-parable to those of new SF6.

● SF6 is contaminated with dangerous substances

● Potential hazard: The SF6decomposition products have an irri-tating or corrosive effect on eyes, skin and respiratory system

The presence of small quantities of gase-ous decomposition products is accompa-nied by clear warning signals in the formof a pungent and unpleasant odour. Irri-tation occurs within seconds, well in ad-vance of any danger arising from poison-ing.

● Protective measures: If health hazardsassociated with the handling of con-taminated SF6 cannot be totally ex-cluded with the aid of technical safetymeasures, then personal protectiveclothing must be worn. Personal safe-ty clothing protects the eyes, the bodyand includes protective breathing ap-paratus.

Additional organisational safety measuresinclude the display of operational instruc-tions and an annual seminar on the po-tential hazards and the safety precautionsto be adopted when handling SF6 which iscontaminated with irritating and corrosivesubstances.

New SF6● SF6 to DIN IEC 376

● Potential hazard: asphyxiation

● Protective measures:Natural and forced ventilation

StorageSulphur hexafluoride is transported as apressurized liquified gas. In Germany, safe-ty precautions and handling practice arebased upon the Order Governing Pressur-ized Containers and its subordinate Techni-cal Regulations.

The containers should not be exposed todirect sunlight and must be secured againstoverturning or rolling.

Storage and work areas must be well ven-tilated. In particular, ventilation must be ef-fective at ground level on account of thefact that SF6 vapour is heavier than air. Ifthe gas is stored underground, appropriateforced ventilation must be provided.

Wherever SF6 is handled, there must be noopen flames (e.g. welding flames) or hotmetal surfaces (e.g. infrared equipment).Eating, drinking and smoking whilst work-ing with SF6 is strictly forbidden.

Although SF6 is recognized as being physi-ologically safe, certain precautions have tobe taken in order to guarantee a safe han-dling of this substance. An important pre-condition is a strict adherence to thethreshold limit value (TLV).

Wherever this cannot be achieved perti-nent safety measures must be selected ac-cording to the degree of potential danger.

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40Sulphur Hexafluoride

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41 Schwefelhexafluorid

Specifications

The SF6 produced by Solvay Fluor undDerivate GmbH is manufactured in a plantthat ensures consistent quality with a purityof min. 99.9 %.

It corresponds to the following guarantee-analysis which in turn conforms to IECRecommendation 376, 1st Edition, Section3 or to DIN IEC 376, Chapter 3 and to VDE0373, Part 1, Chapter 3 (according to thisstandard all values apply to the compositionof the liquid phase).

In general, the impurities in Solvay sulphurhexafluoride are substantially less than themaximum values specified in the guarantee-analysis.

The table on the right shows a typical Solvayquality standards specification.

Prior to shipment, every batch of SF6 is test-ed for physiological safety (cf. Toxicity).

DIN IEC 376

SF6 ≥ 99.90 % by weight

air ≤ 500 ppm by weight (0.25 Vol.-%)

CF4 ≤ 500 ppm by weight (0.1 Vol.-%)

H2O ≤ 15 ppm by weight (0.012 Vol.-%)

mineral oil ≤ 10 ppm by weight

acidity, in terms of HF ≤ 0.3 ppm by weight

hydrolyzable fluorides, in terms of HF ≤ 1 ppm by weight

Solvay Fluor standard specifications

SF6 ≥ 99.98 % by weight

air ≤ 150 ppm by weight

CF4 ≤ 50 ppm by weight

H20 ≤ 0.65 ppm by weight

mineral oil ≤ 10 ppm by weight

acidity, in terms of HF ≤ 0.3 ppm by weight

hydrolyzable fluorides, in terms of HF ≤ 1 ppm by weight

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42Sulphur Hexafluoride

fig. 39 Special high-capacity container for SF6:test pressure 70 barcapacity 600 ltare Ø 465 kg

Packaging for SF6according to IEC 376

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43 Schwefelhexafluorid

Solvay sulphur hexafluoride is shipped as apressure-liquefied gas in steel cylinders ofvarious sizes. The filling level is 1.04 kg (attest pressure 70 bar) and 1.3 kg (at testpressure 250 bar) SF6 per litre of containervolume.

SF6 is supplied in steel cylinders of 5, 10,20, 40, 50 and 52 kg capacity. For largerquantities, special high-capacity containersare available on loan. These accommodate 600 kg of SF6 (see fig. 39). Tube trailers canbe used for export overseas.

The pressurized containers are fitted with aspecial gas-cylinder valve. The valves havean external threaded port mounted on theside with the designation W 21.8 x 1/14"(connection No. 6 to DIN 477). This side-connection piece is protected from con-tamination and damage by means of a hex-agon cap nut. The screw-on safety cap pro-tects the valve from mechanical damageand contamination.

In order to avoid any suck-back of othergases, SF6 pressure-gas containers shouldnever be emptied to such a degree that apartial vacuum occurs. After the containershave been emptied, the cylinder valvesmust be closed immediately. Please returnempty cylinders in a suitable condition forrefilling to us at the following address:

Solvay Fluor und Derivate GmbHCarl-Ulrich-Straße 34D-74206 Bad Wimpfen am NeckarGermany

Railway station:Bad Friedrichshall-Jagstfeld

fig. 40 Steel cylinder for SF6:test pressure 250 barcapacity 40 ltare Ø 48 kg

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44Sulphur Hexafluoride

The Responsible Care Programme for SF6

SF6 – a reusable commoditySF6 is a user-friendly product which besidesits many other positive characteristics can berecycled as well. This is increasingly the im-portant, particularly today.

This is why Solvay Fluor und Derivate GmbHtogether with the producer of SF6 mainte-nance equipment DILO Armaturen undAnlagen GmbH developed a common con-cept for the re-use of SF6, based on many

years of experience. The practical side of thisapproach is illustrated by the following dia-gram.

As an additional service, an analysis can beconducted on your used SF6 gas. Detailedinformation can be found in the brochure“Analysis of Used SF6”.

You will find further information in thebrochure “Concept of Reuse of Used SF6gas”, available upon request.

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45 Sulphur Hexafluoride

Transport by Road40 l steel cylinders and 600 l high-capacitycontainers (see fig. 38) are available. Thepressurized containers are fitted with a spe-cial gas-cylinder valve, external threadedport connection No. 8 (to DIN 477). This isnecessary because corrosive decompositionproducts could be present.

In documents, the product has to be de-clared as follows:

Transport of used SF6

liquefied gas mixture, toxic, n.o.s. (Sulphur Hexafluoride > 95 wt % andHydrogen Fluoride < 2 wt %)

GGVS/ADR – GGVE/RID

UN Nr. 3308

Class 2, T, C

Danger label: 6.1 + 8 (for toxic, corrosive substances)

fig. 41 Packaging for used SF6

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46Sulphur Hexafluoride

Life cycle assessment study"Electricity supply using SF6 technology"

The manufacturers of sulphur hexafluorideswitchgear stations, the utilities and we as apoducer of SF6 place great emphasis on en-vironmental concerns in the use of this prod-uct. For this reason, a SF6 ReUse-conceptwas established years ago, supported byequipment manufacturers, electricity utilities,trade associations and Solvay Fluor undDerivate GmbH. Thus one of the essentialprerequisites for establishing a closed prod-uct cycle for the main quantities of SF6 usedhas been met.

In view of obligations that may arise fromthe Kyoto Protocol, switchgear manufactur-ers, utilities and SF6 producers felt it to benecessary to take their responsibility for theproduct still further and quantify the envi-ronmental profile of the use of SF6 as an in-sulating and arc-quenching gas in high-volt-age and medium-voltage switchgears bymeans of a life-cycle assessment. The mainmotive was the need to replace the one-sid-ed focus on the substance-based globalwarming potential of SF6 by an analysis of allthe relevant environmental criteria in thecontext of the use of SF6 in the electric pow-er industry.

This study, entitled “Electricity Supply UsingSF6 Technology“, was performed in cooper-ation of the firms ABB, PreussenElektra Netz,RWE Energie AG, Siemens AG and SolvayFluor und Derivate GmbH. It relates to theconditions in the Federal Republic ofGermany.

The assessment compares conventional andSF6 technology at the levels of switchgearbays and provides a comparison of a munic-ipal power supply network using either air-insulated or SF6-gas-insulated switchgears atthe same level of supply quality. The criteriafor this comparison are the parameters pri-mary energy consumption, space require-ments, global warming potential, acidifica-tion potential and nutrification potential.

Even at the bay level, the use of SF6 technol-ogy offers advantages for four of the five cri-teria of the life cycle assessment study: pri-mary energy consumption, area required,acidification potential, and nutrification po-tential. Switchgear with a high utilizationfactor and/or the low rates of SF6 lossachievable today provide an ecological ad-vantage even for the greenhouse potential.

SolvayFluor und Derivate

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47 Sulphur Hexafluoride

At the level that counts in the end, namelythe power supply system considered (citycovering 40 square kilometres. 130,000 in-habitants, 120 MW peak load and an annu-al consumption of 400 GWh), the followingresults are obtained: designing a power sup-ply network with GIS technology (using SF6)results in a reduction of about 27 percent inthe primary energy consumption, of about86 percent in the area required, of about 21percent in the greenhouse potential (GWP),of about 21 percent in the acidification po-tential (AP), and of about 29 percent in thenutrification potential (NP), compared to de-signing the same network with AIS technol-ogy (without SF6). The transferability of theresults from this sample network has beentested in extensive scenario calculations.

The major reasons for this reduced environ-mental impact are: since SF6 has consid-erably better insulating and quenching prop-erties than air, substations and equipmentcan be made with less material and energythan in the SF6-free AIS alternative.Furthermore, due to the compact design ofthe GIS components, the 110/20-kV trans-former substations can be built directly atthe (downtown) load centers. So the energyis transmitted at high voltage with low loss-es to the city centers, and distributed fromthere to the consumers via short medium-voltage lines.

fig. 42 The use of GIS switchgear in the power supply system considered reduces all the potential environ-mental impacts studied. The diagram shows the relative envi-ronmental impact potentials during the first year of use of the power system variant (blue bars = AIS version, green bars = GIS/SF6 ver-

sion). An increase in the system’s sup-ply capacities by about 50 percent(i.e. increased utilization of the sys-tem) results in a further reduction ofabout 5 percent each in the parame-ters primary energy consumption,greenhouse potential (GWP), acidifi-cation potential (AP), and nutrificationpotential (NP), due to SF6 technology.

The use of SF6 technology leads to consid-erable environmental advantages over theuse of SF6-free switchgear. Therefore, SF6technology makes sense for electric powersupplies, even from the environmental viewpoint. This requires the use of GIS installations that ensure appropriately lowSF6 emissions, on the one hand, and rigorous application of the SF6-ReUse-Concept of a closed SF6 cycle, on the other.

The life cycle assessment was performed ac-cording to the specifications of the interna-tional standard DIN EN ISO 14040, and wasfollowed and evaluated by an external inde-pendent expert from TÜV NORD.

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48Sulphur Hexafluoride

Product stewardship for SF6

Solvay – well known as a global supplier ofnew SF6 gas according to IEC 376 – caresfor the environment. We are your partner forthe SF6 ReUse concept and full technical ser-vices.

The SF6 ReUse concept of Solvay Fluor undDerivate GmbH includes:

● environmental consulting

● analytical services of used SF6

● packaging and transport of used SF6

● reclaiming of used SF6

Solvay Fluor und Derivate GmbH is the onlycompany worldwide delivering such a com-plete range, to fullfil the requirements of theresponsible care programme.

For further information, please refer to ourSF6 ReUse Folder.

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49 Sulphur Hexafluoride

Sales SF6Telephone: +49-(0)511/857-2949

Fax: +49-(0)511/857-2146

eMail: [email protected]

Internet: www.solvay-fluor.de

Technical Service SF6Telephone: +49-(0)511/857-2441

Fax: +49-(0)511/857-2166

eMail: [email protected]

Internet: www.solvay-fluor.de

Inorganic fluorides ● Aluminium fluoride hydrate ● Ammonium fluoride ● Ammonium hydrogen fluoride ● Barium fluoride● Calcium fluoride● Fluoroboric acid● Potassium fluoroaluminate● Potassium hydrogen fluoride● Potassium fluoroborate● Potassium fluorotitanate ● Potassium cryolithe● Synthetic cryolithe● Lithium cryolithe ● Sodium fluoride● Sodium hydrogen fluoride● Nocolok® Flux

(Registered Trademark of Alcan Inter. Ltd.)

We produce world-wide in our works inCatoosa (USA), Frankfurt (Germany),Tarragona (Spain) and Tavaux (France). Theproduction of fluorine compounds is con-centrated at our Bad Wimpfen (Germany)plant.

The product range includes both organicand inorganic compounds:

Fluorocompounds● Fluor (F2)

● Solkane® hydrofluoroalkanesSolkane 22Solkane 23Solkane 123Solkane 141bSolkane 142bSolkane 22/142b mixturesSolkane 134a/152a mixturesSolkane 134aSolkane 143aSolkane 152aSolkane 404aSolkane 407CSolkane 410ASolkane 507

● Solkane 227pharma● Polyetherpolyole: IXOL®

● Flame retardant: KaCeFlam®

● Sulphur hexafluoride (SF6)● Iodine pentafluoride (IF5)● Hydrogen Fluoride● Hydrofluoric acid

Fluorine compounds fromSolvay Fluor und Derivate GmbH

Fine ChemicalsCF3-Aliphatics:● Trifluoroacetic acid ● Trifluoroacetic acid anhydride● Trifluoroacetyl chloride ● Trifluoroacetic acid esters

Trifluoroacetic acid methyl ester Trifluoroacetic acid ethyl ester

● 2,2,2-Trifluoroacetamide ● Alcohols and ketones

2,2,2-Trifluoroethanol 1,1,1-Trifluoroacetone Trifluoroacetophenone

● Trifluoromethyl components 1,1,1-Trichloro-2,2,2-trifluoroethan

CF2-Aliphatics:

● Chlorodifluoroacetic acid● Chlorodifluoroacetyl chloride● Difluoroacetic acid esters

Difluoroacetic acid methyl esterDifluoroacetic acid ethyl ester

Your Solvay Contact

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Bibliography

50Sulphur Hexafluoride

[1] K. K. Maggon, Medical uses of sul-phur hexafluoride, (Review Article)Drugs of the Future 1994, 19(12):1101-1107

[2] IMA Technical Committee Report„Recommended practices for conser-vation of sulfurhexafluoride in mag-nesium melting operations“

[3] G. Schemm, „Gießerei“, 58 (1971)19, 558-65

[4] M. Colditz, Chem.-lng.-Techn. 19(1972) 1116-1120

[5] W. M. Hickam and R. E. Fox, J. Chem. Phys. 25 (1956) 4, 642-47

[6] D. Berg, J. Chem. Phys. 31 (1959)572-3

[7] E. Steiniger, Dissertation TU Berlin 1964

[8] A. Hartig, Beiheft 3 der Elektrotechn.Zeitschrift, 1966

[9] Electra 32 (Jan. 1974) 61-82

[10] J. W. Gibson and E. F. Miller, J. Elektrochem. Soc. 100(1953) 265-71

[11] G. Frind, Z. Angew. Physik 12 (1960)5, 231-37

[12] T. Milek, Sulfur Hexafluoride-DataSheets DS 140. Air force systemscommand Contr. AF 33 (615) -1235(Oct. 1964) AD 607 949

[13] Dampftafel für SF6, Kali-Chemie AG,1979

[14] VDI Wärmeatlas, 7. Auflage

[15] J. T. Asthon a. o., J. Chem. Soc. (A) 1968,1793-96

[16] Vanderkool, AIEE Feb. 1-6 (1959),Paper No. CP 59-258

[17] A. Eucken and E. Schröder, Z. Phys. Chem. B 41 (1933) 307-19

[18] P. A. G. O’Mare, J. C. Bettle and W. N. Hubbard, Trans Faraday, Soc. 62C196W558

[19] M. Trautz, K. Ehrmann, J. prakt.Chem. 142 (1935) 79-124

[20] J. W. Frühling and D. J. Hanawalt, Mod. Cast. 56, U 969 Nr. 2 (1969)159-64

[21] W. Becher and J. Massonne,Elektrotechn. Zeitschr. A 91 (1970)11, 605-10

[22] H. R. Sheppard, Insulation, (May 1962) 21-25

● SF6 ReUse Folder

● Life cycle assessment study “Electricitysupply using SF6 technology“

● “SF6 ReUse Concept and New Applications”; Pittroff, Schütte, Meier8th Int. Symp. On Gaseous Dielectrics; 1998 p. 465 – 470

● “Life Cycle Assessment Electricity Supply Using SF6-Technology”; Preissegger, Dürschner, Klotz, Krähling, Neumann, Zahn; IPCC 2nd International Symposium on NON-CO2 Greenhouse Gases 8 –10.09.99

● “Separation of SF6 / N2 Mixtures”;Pittroff, 2nd European Conference of Industrial Electrical Equipment and Environment; 24 – 25.01.00

Please note that all users of SF6 are respon-sible for adherence to applicable instructionsand regulations and for the observance ofcurrent laws.

The information given in this brochure hasbeen compiled to the best of our knowl-edge; no liability can be accepted in mattersarising therefrom.

Further publications about SF6by Solvay Fluor

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Solvay Fluor und Derivate GmbH

Hans-Böckler-Allee 20D-30173 Hannover

Telephone: +49-(0)-511-8 57-0Fax: +49-(0)-511-28 2126

Internet: http://www.solvay-fluor.com


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