Impact of SF6 Gas-Filled
Switchgear on the Environment
Data Bulletin
6065DB1201
2012
CONTENTS
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page
Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SF6 Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Technological Advantages of SF6 in Switchgear . . . . . . . . . . . . . . . . . . . .
Other Industries Using SF6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SF6 and the Greenhouse Effect. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SF6 By-Products and Toxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Handling of SF6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Legislature on SF6 in the Electric Industry. . . . . . . . . . . . . . . . . . . . . . . . .
Schneider Electric North America SF6-filled Switchgear Data . . . . . . . . . .
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Impact of SF6 Gas-Filled Switchgear on the Environment
Executive Summary
In the recent years, there has been a considerable amount of controversy around the use of
Sulfur Hexafluoride (SF6) in the electrical distribution industry. For over 50 years, SF6 has been widely
used in medium voltage (MV) and high-voltage (HV) products as an insulating and dielectric material.
Pure SF6 gas is colorless, odorless, nontoxic, and non-flammable, however it is a highly potent green
house gas with a global warming potential of 23,900 1. Despite the high warming potential, contribution
of SF6 emissions from MV and HV electrical switchgear to climatic change is marginal and accounts
for approximately 0.1% of world greenhouse gas emissions. 2
In this paper, I will highlight the properties of SF6 that make it such a favorable gas for the electric
industry, its greenhouse effect, and current legislature on the use of SF6 in electrical equipment. I will
also review the use of SF6 in Schneider Electric’s MV switchgear portfolio for North America.
SF6 Properties
SF6 is one of the heaviest known gases, with a density almost five times higher than that of air. The
excellent dielectric properties of SF6 are due to the electronegative character of its molecule. The
dielectric strength of SF6 is about 2.5 times higher than that of air under the same conditions. SF6 does
not contribute to ozone depletion as it contains no chlorine.
Characteristics of SF6 that make it a very suitable for electrical equipment are:
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High dielectric strength
Excellent arc-quenching properties
Good chemical stability
Nontoxic in its pure state
Technological Advantages of SF6 in Switchgear
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High breaking capacity and low operating energy (SF6 quenching properties are 100 times higher
than air) when used as an interrupting medium 3
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Reduction of insulation volumes (SF6 is twice as effective as air) and better heat dissipation than
air insulated equipment allow gas-insulated switchgear (GIS) to have a much smaller footprint
•
The smaller footprint reduces copper and steel used, which in itself reduces impact on the
environment of processing those materials
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The shorter copper runs also result in reduced heat loss to the atmosphere
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Reduced maintenance of main contacts and other components enclosed in SF6 sealed-for-life
enclosures
•
High continuity of service as components enclosed in SF6 sealed-for-life enclosures are not
affected by external environmental conditions
•
SF6 enclosed equipment reduces the risk of arcing and partial discharge
Very limited space required for installation when compared to air-insulated equipment. This is very
critical for retrofit applications and areas having limited real estate availability
1
Emissions of Fluoridated Gases, United States Environmental Protection Agency, accessed December 17, 2012,
http://www.epa.gov/highgwp/scientific.html.
2
P. O’Connell, F. Heil, J. Henriot, G. Mauthe, H. D. Morrison, L. Niemeyer, M. Pittroff, R. Probst, and J. P. Taillebois. SF6 in the Electric
Industry, Status 2000, CIGRE Study Committee 23, 2001.
3
D. Koch, Cahier Technique no.188: SF6 properties, and use of in MV and HV switchgear, Schneider Electric, 2003;
Serge Théoleyre, Cahier Technique no. 193: MV breaking techniques, Schneider Electric, 1999.
© 2012 Schneider Electric USA, Inc.
All Rights Reserved
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12/2012
Impact of SF6 Gas-Filled Switchgear on the Environment
Other Industries Using SF6
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Medical applications—X-ray machines
Tracer gas—studying airflow in ventilation systems
Metallurgical processing—aluminium and magnesium
SF6 and the Greenhouse Effect
As shown in the following illustration4, greenhouse gases allow shortwave energy from direct sunlight
to pass through and reach the earth’s surface, but trap the reflected long wave energy, thereby
allowing less heat to escape back to space.
Top Ten Greenhouse Gases 5
1. Water Vapor
2. Carbon Dioxide
3. Methane
4. Nitrous Oxide
5. Ozone
6. Trifluoromethane
7. Hexafluoroethane
8. Sulfur Hexafluoride (SF6)
9. Trichlorofluoromethane
10. Sulfuryl Fluoride
4
Atmosphere: Change is in the Air, The Smithsonian Institution, accessed December 17, 2012,
http://forces.si.edu/atmosphere/02_04_07.html.
5
The Top Ten Greenhouse Gases, Popular Science, posted March 17, 2009, http://www.popsci.com/node/33141.
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© 2012 Schneider Electric USA, Inc.
All Rights Reserved
Impact of SF6 Gas-Filled Switchgear on the Environment
SF6 By-Products and Toxicity
In its pure state, SF6 has no toxicity. In an electric arc, due to the high temperature, a small portion of
SF6 is decomposed. SF6 decomposition only happens when it is used as an arc quencher. When SF6
is used as an insulating medium around vacuum interrupters, no by-products are produced.
Table 1:
Gaseous SF6 Decomposition By-Products and Typical Concentrations During
Repeated Sparking
Chemical Formula
Chemical Name
Chemical Abstracts
Service Registry Number
Experimental
Concentration
(percentage by volume)
HF
Hydrogen fluoride
7664-39-3
1.0
SOF2 (SF4) b
Thionyl sulfide (sulfur
tetrafluoride)
7783-42-8 (7783-60-0)
0.5
SOF4
Sulfur tetrafluoride oxide
13709-54-1
0.085
SiF4
Silicon tetrafluoride
7783-61-1
0.085
S2F10 (SF5) c
Disulfur decafluoride
5714-22-7
0.025
SO2F2
Sulfuryl fluoride
2699-79-8
0.006
SO2
Sulfur dioxide
7446-09-5
0.002
Some of the by-products, namely SOF2, SO2, HF, and S2F10 pose health threats (taking into account
reaction quantities and toxicity). S2F10 is the most toxic. 6
The health effects of these by-products could be:
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Eye, nose and throat irritation
Pulmonary edema, skin and eye burns, nasal congestion, and bronchitis
These by-products are only produced at very high temperatures and only when SF6 is used as an
interrupting medium and not as a insulating medium. These by-products are contained within the
sealed-for-life enclosures.
In the case of arc-resistant switchgear, if there is a short circuit inside the switchgear (internal arc), the
pressure, arc flash, and SF6 will be vented out of the switchgear. This exhaust would contain SF6
by-products and any exposure to the gas for more than eight hours/day would be harmful to personnel
if the threshold limit value (TLV) of the by-product present in the atmosphere is greater than 1.6 ppmv.
There is a very low probability of internal arcing in MV gas-insulated switchgear.
6
Byproducts of Sulfur Hexafluoride (SF6) Use in the Electric Power Industry, ICF Consulting, 2002.
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© 2012 Schneider Electric USA, Inc.
All Rights Reserved
Impact of SF6 Gas-Filled Switchgear on the Environment
Handling of SF6 Gas 7
The SF6 gas inside the gas insulated sealed-for-life enclosure is at very low pressure. No gas handling
is required by the user during the entire life cycle of the product.
As SF6 is an expensive gas and is characterized by a high degree of stability, it is convenient to
recover and reuse the gas at the end of life of the equipment. Third parties carry out the end of life
dismantling and can support with the recycling and disposal of SF6 from the equipment.
Legislation on SF6 in the Electric Industry
In California, the Air Resource Board (ARB) developed the SF6 GIS Final Regulation Order which
became effective on June 17, 2011. Per the Order, the maximum annual SF6 emission rate for each
GIS owner's active GIS equipment shall be reduced to 1% by 2020. 8
By June 1, 2012, and June 1st of each year thereafter, each GIS owner must submit an annual report to
the Executive Officer reporting the emissions that occurred during the previous calendar year. This report
must declare the annual SF6 emissions and emission rate per the equations provided in the report.
The Environmental Protection Agency (EPA) has made greenhouse gas reporting mandatory in the
United States. Electrical equipment manufacturers fall under categories DD, QQ, and SS, and thus
are not required to report until 2013. Electrical equipment manufacturers have to report the amount of
SF6 they purchase only if the amount is greater than 17,280 lbs. This does not necessarily relate to
how much is lost from their product during manufacturing, or their leakage rate. There is no current or
new proposed legislation by the U.S. Congress underway. The hope is that voluntary actions by all
involved parties will solve the issue; however, the U.S. Congress will be monitoring actions and, if
results are not forthcoming, then action will take place.
7
CAPIEL, Switchgear and SF6 Gas, CAPIEL HV-ESDD1-R1-1.02, 2002.
8
California Environmental Protection Agency, Sulfur Hexafluoride (SF6) Emission Reductions from Gas Insulated Switchgear,
web page last reviewed May 16, 2012, http://www.arb.ca.gov/cc/sf6elec/sf6elec.htm.
© 2012 Schneider Electric USA, Inc.
All Rights Reserved
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12/2012
Impact of SF6 Gas-Filled Switchgear on the Environment
Schneider Electric North America SF6-filled Switchgear Data
HVL/cc (Metal Enclosed Switchgear)
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Weight of SF6 gas (Kg/Lb)—0.1 kg / 0.29 lbs per switch
Pressure of SF6 gas—0.4 bar (absolute)
Leakage rate per year—less than 0.1%
GHA (GIS)
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Weight of SF6 gas (Kg/Lb)—4.5 kg / 9.9 lbs per section
Pressure of SF6 gas—1.3 bar (absolute)
Leakage rate per year—less than 0.1%
SF6 used as an insulating medium and not as an interrupting medium
VOX (Station Breaker)
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Weight of SF6 gas (Kg/Lb)—2.9 kg / 6.4 lbs per unit
Pressure of SF6 gas—1.5 bar (absolute)
Leakage rate per year—less than 0.1%
SF6 used as an insulating medium and not as an interrupting medium
DVCAS (Metal Enclosed Switchgear)
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Weight of SF6 gas (Kg/Lb)—3.06 kg / 6.7 lbs per section
Pressure of SF6 gas—0.3 bar (absolute)
Leakage rate per year—less than 0.1%
SF6 used as an insulating medium and not as an interrupting medium
N-Series (Recloser)
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Weight of SF6 gas (Kg/Lb)—1.8 kg / 4 lbs per unit
Pressure of SF6 gas—0.35 bar (absolute)
Leakage rate per year—less than 0.1%
RL-Series (Recloser)
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Weight of SF6 gas (Kg/Lb)—1.0 kg / 2.2 lbs per unit
Pressure of SF6 gas—1.0 bar (absolute)
Leakage rate per year—less than 0.1%
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© 2012 Schneider Electric USA, Inc.
All Rights Reserved
Impact of SF6 Gas-Filled Switchgear on the Environment
Conclusion
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There is no restriction on use of SF6 in electrical switchgear.
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There is no known substitute with similar properties of SF6 gas.
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In its pure state, SF6 is a non-toxic gas. It is not hazardous for people and contains no pollutants. It
is non-flammable.
SF6 technology currently offers the best possible solution in terms of cost, use of natural resources,
efficiency, safety, and compactness of MV electrical switchgear.
Schneider Electric equipment sold in the U.S. has a minimal amount of SF6 gas under very low
pressure and a less than 0.1% leakage rate per year.
© 2012 Schneider Electric USA, Inc.
All Rights Reserved
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12/2012
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6065DB1201
12/2012