Sulfur Hexafluoride For Electrical Applications - Work On the Internet

Sulfur hexafluoride is a colourless, odourless gas having a much higher dielectric strength than air or nitrogen. The SF6 is often used as Dielectric medium in gas insulated switchgears, HV circuit breakers and other electrical equipment.

Sulfur hexafluoride is a very potent greenhuse gas, (22800 times more than CO2). That???s why this gas is under the F-Gas directive in Europe. SF6 can???t be released to the atmosphere.

The arcing or corona in SF6 breakers can degenerate the gas into corrosive or toxic compounds, such as S2F10, or SO2. It is advisable for electric maintenance companies to monitor the gas composition and quality by means of an SF6 Analyzer.

Properties of SF6

Physical

Formula: SF6
Molecular weight: 146.05
Sublimation temperatures, at 1 atm: -63.9 °C
-83 °F
Melting point, at 32.5 psia: -50.8 °C
-59.4 °F
Density of gas, at 21.1°C, 1atm: 6.139 g/l
at 70°F, 1 atm: 0.382 g/l
relative to air = 1, at 70°F, 1 atm: ~5
Surface tension, at -20°C: 8.02 dyne/cm
Viscosity
liquid, at 13.52°C: 0.305 cp
gas, at 31.16°C: 0.0157 cp
Index of refraction, at 0°C, 760 mm Hg: 1.0157 nD
Critical temperature, TC: 318.80 K
Critical pressure, PC: 37.772 bars
318.80 atm
Critical volume, VC: 1.356 cm3/g
0.198 liters/g???mole
Solubility of SF6, at 1 atm, in
transformer oil, at 27°C: 4.408 ml of SF6/ml oil
water. At 24.85°C: ~0.0055 cm3 SF6 (STP)/cm3 H20
Solubility of water in SF6: ~0.0097 % by wt

Electrical:

Dielectric strength (rel N2 = 1) at 60 Hz-1.2 MHz: ~2.3-2.5
Dielectric constant at 25°C, 1 atm: 1.002049
Loss tangent. tan ?. 1 atm: Thermodynamic:
Heat of sublimation: 5640 cal/g???mole
Heat of fusion: 1200 cal/g???mole
Heat of vaporization, at 70°F: 28.38 Btu (ISU)/lb
15.767 or at 25°C, cal/g
Free energy of formation, at 25°C, ???G: -291,77 kcal/g???mole
Molar heat capacity, at 298°K: 23.22 cal/g???mole??? °C
Thermal conductivity, 30°C: 3.36 x 10-5 cal/sec???cm???°C
Enthalpy at 70°F, 1 atm: 61.9474 Bt
Entropy at 70°F, 1 atm: 0.15887 Btu/lb???°R
Base enthalpy and entropy = 0.00 at -40°F

Transport of SF6

Sulfur hexafluoride is shipped steel cylinders as a liquefied gas in equilibrium with its own vapours.
The manufacturer shall be able to certify that the material is at least as non-toxic as Group V1 of the Underwriters Laboratories classification.
Product meets the following ASTM specification D2474-75:

Water content, max dew point: -45°C
Hydrolysable fluorides, expressed as HF acidity: 0.3 max ppm by wt
Air expressed as N2, max: 0.05 wt %
Carbon tetrafluoride, max: 0.05 wt %
Molecular weight: 146 =2%
Assay, min: 99.8 wt %
(corresponds to a water content of 8.9 ppm by weight or 71 ppm by volume)

Vapor pressure and density of SF6

TEMPERATUR EºC - VAPOR PRESSURE,PSIG - LIQUID DENSITY LB/CU FT - VAPOR DENSITY LB/CU FT

-58 -- 9,19 -- 115,4 -- 1,251

-48 -- 27,55 -- 113,7 -- 1,542

-38 -- 38,48 -- 111,9 -- 1,886

-28 -- 49,17 -- 110,1 -- 2,290

-18 -- 62,81 -- 108,1 -- 2,765

-8 -- 78,60 -- 106,2 -- 3,318

0 -- 92,91 -- 104,5 -- 3,826

10 -- 113,08 -- 102,4 -- 4,552

20 -- 135,96 -- 100,1 -- 5,396

30 -- 161,77 -- 97,7 -- 6,377

40 -- 190,70 -- 95,2 -- 7,519

50 -- 222,98 -- 92,4 -- 8,857

60 -- 258,82 -- 89,4 -- 10,439

70 -- 298,49 -- 86,1 -- 12,336

80 -- 342,30 -- 82,4 -- 14,669

90 -- 390,70 -- 77,9 -- 17,657

100 -- 444,36 -- 72,2 -- 21,823

110 -- 504,50 -- 62,9 -- 29,147

114,15 -- 531,89 -- 45,3 -- 36,398

TEMPERATUR EºC - VAPOR PRESSURE(BAR) - LIQUID DENSITY(KG/M3) - VAPOR DENSITY (KG/M3)

-50,0 -- 1,323 -- 18482,8 -- 200,4

-44,4 -- 1,900 -- 18207,4 -- 247,0

-38,9 -- 2,653 -- 17923,1 -- 302,1

-33,3 -- 3,390 -- 17628,7 -- 366,9

-27,8 -- 4,330 -- 17323,2 -- 442,8

-22,2 -- 5,419 -- 17005,2 -- 531,5

-17,8 -- 6,406 -- 16740,9 -- 612,8

-12,2 -- 7,796 -- 16396,4 -- 729,2

-6,7 -- 9,374 -- 16034,0 -- 864,3

-1,1 -- 11,154 -- 15650,6 -- 1021,4

4,4 -- 13,149 -- 15242,1 -- 1204,5

10,0 -- 15,374 -- 14802,9 -- 1418,7

15,6 -- 17,845 -- 14325,0 -- 1672,2

21,1 -- 20,580 -- 13796,1 -- 1976,1

26,7 -- 23,601 -- 13195,4 -- 2349,7

32,2 -- 26,938 -- 12484,5 -- 2828,3

37,8 -- 30,638 -- 11571,3 -- 3495,8

43,3 -- 34,784 -- 10076,4 -- 4669,0

45,6 -- 36,673 -- 7250,0 -- 5830,4

This content has been taken from http://www.ideamarketers.com/?articleid=3595454&CFID=245070268&CFTOKEN=64961529

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