Impact of SF 6 Gas-Filled Switchgear on the Environment

Transcription

1 Impact of SF 6 Gas-Filled Switchgear on the Environment Data Bulletin 6065DB CONTENTS Description Page Executive Summary SF6 Properties Technological Advantages of SF6 in Switchgear Other Industries Using SF SF6 and the Greenhouse Effect SF6 By-Products and Toxicity Handling of SF Legislature on SF6 in the Electric Industry Schneider Electric North America SF6-filled Switchgear Data Conclusion

2 Executive Summary In the recent years, there has been a considerable amount of controversy around the use of Sulfur Hexafluoride (SF 6 ) in the electrical distribution industry. For over 50 years, SF 6 has been widely used in medium voltage (MV) and high-voltage (HV) products as an insulating and dielectric material. Pure SF 6 gas is colorless, odorless, nontoxic, and non-flammable, however it is a highly potent green house gas with a global warming potential of 23, Despite the high warming potential, contribution of SF 6 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 SF 6 that make it such a favorable gas for the electric industry, its greenhouse effect, and current legislature on the use of SF 6 in electrical equipment. I will also review the use of SF 6 in Schneider Electric s MV switchgear portfolio for North America. SF 6 Properties SF 6 is one of the heaviest known gases, with a density almost five times higher than that of air. The excellent dielectric properties of SF 6 are due to the electronegative character of its molecule. The dielectric strength of SF 6 is about 2.5 times higher than that of air under the same conditions. SF 6 does not contribute to ozone depletion as it contains no chlorine. Characteristics of SF 6 that make it a very suitable for electrical equipment are: High dielectric strength Excellent arc-quenching properties Good chemical stability Nontoxic in its pure state Technological Advantages of SF 6 in Switchgear High breaking capacity and low operating energy (SF 6 quenching properties are 100 times higher than air) when used as an interrupting medium 3 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 The shorter copper runs also result in reduced heat loss to the atmosphere 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 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 1 Emissions of Fluoridated Gases, United States Environmental Protection Agency, accessed December 17, 2012, 2 P. O Connell, F. Heil, J. Henriot, G. Mauthe, H. D. Morrison, L. Niemeyer, M. Pittroff, R. Probst, and J. P. Taillebois. SF 6 in the Electric Industry, Status 2000, CIGRE Study Committee 23, D. Koch, Cahier Technique no.188: SF 6 properties, and use of in MV and HV switchgear, Schneider Electric, 2003; Serge Théoleyre, Cahier Technique no. 193: MV breaking techniques, Schneider Electric,

3 Other Industries Using SF 6 Medical applications X-ray machines Tracer gas studying airflow in ventilation systems Metallurgical processing aluminium and magnesium SF 6 and the Greenhouse Effect As shown in the following illustration 4, 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 (SF 6 ) 9. Trichlorofluoromethane 10. Sulfuryl Fluoride 4 Atmosphere: Change is in the Air, The Smithsonian Institution, accessed December 17, 2012, 5 The Top Ten Greenhouse Gases, Popular Science, posted March 17, 2009, 3

4 SF 6 By-Products and Toxicity In its pure state, SF 6 has no toxicity. In an electric arc, due to the high temperature, a small portion of SF 6 is decomposed. SF 6 decomposition only happens when it is used as an arc quencher. When SF 6 is used as an insulating medium around vacuum interrupters, no by-products are produced. Table 1: Gaseous SF 6 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 SOF2 (SF4) b Thionyl sulfide (sulfur tetrafluoride) ( ) 0.5 SOF4 Sulfur tetrafluoride oxide SiF4 Silicon tetrafluoride S2F10 (SF5) c Disulfur decafluoride SO2F2 Sulfuryl fluoride SO2 Sulfur dioxide 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: 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 SF 6 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 SF 6 will be vented out of the switchgear. This exhaust would contain SF 6 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. 4 6 Byproducts of Sulfur Hexafluoride (SF 6 ) Use in the Electric Power Industry, ICF Consulting, 2002.

5 Handling of SF 6 Gas 7 The SF 6 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 SF 6 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 SF 6 from the equipment. Legislation on SF 6 in the Electric Industry In California, the Air Resource Board (ARB) developed the SF 6 GIS Final Regulation Order which became effective on June 17, Per the Order, the maximum annual SF 6 emission rate for each GIS owner's active GIS equipment shall be reduced to 1% by 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 SF 6 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 Electrical equipment manufacturers have to report the amount of SF 6 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 SF 6 Gas, CAPIEL HV-ESDD1-R1-1.02, California Environmental Protection Agency, Sulfur Hexafluoride (SF 6 ) Emission Reductions from Gas Insulated Switchgear, web page last reviewed May 16, 2012, 5

6 Schneider Electric North America SF 6 -filled Switchgear Data HVL/cc (Metal Enclosed Switchgear) Weight of SF 6 gas (Kg/Lb) 0.1 kg / 0.29 lbs per switch Pressure of SF 6 gas 0.4 bar (absolute) GHA (GIS) Weight of SF 6 gas (Kg/Lb) 4.5 kg / 9.9 lbs per section Pressure of SF 6 gas 1.3 bar (absolute) SF 6 used as an insulating medium and not as an interrupting medium VOX (Station Breaker) Weight of SF 6 gas (Kg/Lb) 2.9 kg / 6.4 lbs per unit Pressure of SF 6 gas 1.5 bar (absolute) SF 6 used as an insulating medium and not as an interrupting medium DVCAS (Metal Enclosed Switchgear) Weight of SF 6 gas (Kg/Lb) 3.06 kg / 6.7 lbs per section Pressure of SF 6 gas 0.3 bar (absolute) SF 6 used as an insulating medium and not as an interrupting medium N-Series (Recloser) Weight of SF 6 gas (Kg/Lb) 1.8 kg / 4 lbs per unit Pressure of SF 6 gas 0.35 bar (absolute) RL-Series (Recloser) Weight of SF 6 gas (Kg/Lb) 1.0 kg / 2.2 lbs per unit Pressure of SF 6 gas 1.0 bar (absolute) 6

7 Conclusion There is no restriction on use of SF 6 in electrical switchgear. In its pure state, SF 6 is a non-toxic gas. It is not hazardous for people and contains no pollutants. It is non-flammable. There is no known substitute with similar properties of SF 6 gas. SF 6 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 SF 6 gas under very low pressure and a less than 0.1% leakage rate per year. 7

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