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Halogenated substances are
chemicals that have been engineered for a variety of industrial uses. Some are
greenhouse gases with high global warming potentials (GWPs) as compared with
carbon dioxide and, therefore, may have an effect on global climate
disproportionate to the relatively small volumes emitted.
Emissions of halogenated substances can be
classified into two groups. One group consists of chlorofluorocarbons
(CFCs), hydrochlorofluorocarbons (HCFCs), and other chlorine-containing
gases whose phase-out is governed by the Montreal Protocol. The United
Nations Framework Convention on Climate Change (UNFCCC) excludes from its
provisions gases covered by the Montreal Protocol and, therefore, does not
address CFCs and HCFCs.
The halogenated substances in the second
group include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur
hexafluoride (SF6). These compounds are also potent greenhouse
gases. In contrast to the chlorine-containing halogenated substances, these
compounds do not destroy ozone, and as such are not governed by the Montreal
Of particular interest to the electric
power sector is SF6. Sulfur hexafluoride is used as an insulator
for circuit breakers, switch gear, and other electrical equipment. The
electric power industry uses roughly 80% of all SF6 produced
worldwide. SF6 has a very high GWP – 23,900 times the warming
effect of carbon dioxide per ton emitted. Therefore, even small amounts of
SF6 emissions can constitute a significant carbon-equivalent
Under ideal operating conditions, SF6
would remain contained within transmission and distribution equipment. In
reality, however, SF6 is inadvertently emitted into the
atmosphere during various stages of the equipment’s life cycle. Leaks
generally increase as equipment ages. Fugitive emissions can escape through
valve fittings and at joints between flanges and porcelain bushings. SF6
can be accidentally released at the time of equipment installation as well
as during servicing.
In order to address this challenge,
members of the electric power industry and EPA have come together in a
collaborative effort to reduce SF6 emissions.
1999, EPA created the “SF6
Partnership for Electric Power Systems” to help the electric power
industry reduce its emissions of SF6.
More than 70 electric utilities currently participate in EPA’s
Each year, the program’s participants have
exceeded their goals for reducing SF6 emissions. According to
2007 Annual Report, SF6
Partners in 2007 have collectively
achieved a 64-percent decrease in emissions from the 1999 baseline year.
Approximately 366,538 pounds of SF6, or the equivalent
MMTCO2 emissions were avoided in 2007. Cumulatively (1999-2007),
emissions avoided total 1,554,278 pounds or 16.85 MMTCO2e.
The SF6 emissions data reported
to EPA were further analyzed to identify the trend in SF6
emissions reductions from the 2000-2002 base period used by
Power Partners℠ and to update
the estimated equivalent amount of CO2 emissions using the latest
global warming potential equivalence factors. The results show that the
power sector avoided a cumulative total of 3.4 million tons of CO2
emissions from the 2000-2002 base-period average through 2005. This is shown
in the figure below:
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When Duquesne Light Company
decommissioned its Carson Substation in Pennsylvania,
the company paid careful attention to ensure the project was completed in
an environmentally responsible manner. As part of the decommissioning
process, the company worked with a vendor to recover and safely remove the
SF6 gas. As a result, nearly 7,300 pounds of SF6 were
removed, instead of being released in the atmosphere. This is equivalent to
the CO2 emissions reductions realized from removing 17,000 cars
from the road for one year.
As part of
Exelon’s ComEd and PECO subsidiaries’ participation in the EPA
Partnership, the companies set a joint SF6 goal in March 2006,
committing to achieve a leak rate for SF6 of no more than 10
percent for 2006. To help achieve this goal, the companies provided
additional training to substation
personnel on the proper handling of SF6 gas to minimize leaks and
revised SF6 handling procedures.
Great River Energy (GRE)
reduced its 2005 SF6 emissions to
half of its 1998 baseline of 3,335 pounds through additional employee
awareness training; monitoring SF6 equipment for leaks; replacing
old, large-volume equipment with smaller more efficient equipment; and
investigating other available technologies.
Lower Colorado River Authority’s
participation in EPA’s SF6 Emissions Reduction Partnership
resulted in the reduction of 1,800 pounds of SF6 emissions in
2005 through circuit breaker replacements.
As part of MidAmerican Energy’s
participation in EPA’s Partnership, the utility replaces at least three
circuit breakers that leak SF6 each year. To date, 13 345-kV
circuit breakers have been replaced, and SF6 emission rates have
decreased from 23.9 percent in 2000 to 9.5 percent in 2005.
Since 1999, Northeast Utilities
has reduced its SF6 emission rate by over 90 percent, a great
achievement given that the utility has experienced significant transmission
system growth during this period. These emission reductions were achieved in
part through a dedicated equipment
Public Utility District No. 1 of
Douglas County, Washington has reduced emissions
of SF6 through proper handling techniques, identification and
elimination of leaks, and the replacement of equipment that do not meet
specific leak rate thresholds. Douglas PUD successfully reduced its emission
rate to zero in 2004 and continues to maintain zero emissions as of 2005.
Southern California Edison (SCE)
received an EPA award for preventing nearly 110,000 pounds of SF6
emissions from entering the atmosphere from
1999 to 2005. This reduction is equivalent to removing 250,000 cars from the
road for one year. Since joining the EPA partnership in 2001, SCE has
reduced its SF6 emissions by 32 percent.
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Environmental Protection Agency,
“Reducing SF6 Emissions Means Better Business for Utilities: PG&E
The experience of PG&E can
help other utilities in meeting their environmental and operational goals
through cost-effective solutions to reduce SF6 loss.
Agency, “SF6 Emissions Reduction Partnership for Electric Power
The SF6 Emission
Reduction Partnership for Electric Power Systems is a collaborative effort
between EPA and the electric power industry to identify and implement
cost-effective solutions to reduce sulfur hexafluoride (SF6)
emissions. Currently over 70 utilities participate in this EPA
Environmental Protection Agency, “SF6
Emissions Reductions Partnership for Electric Power Systems: 2007 Annual
Report” (December 2008)
EPA’s annual report for the
SF6 Emission Reduction Partnership for Electric Power Systems
documents the Partnership’s progress in abating SF6
emissions through cost-effective practices and technologies. Cumulative SF6
emissions avoided by partners since 1999 are presented, as well as the
latest results reported by partners for 2007.
Environmental Protection Agency, “SF6
Emissions Reporting Protocol” (spreadsheet)
link will launch an Excel spreadsheet to assist in SF6 reporting
to EPA's program. The Excel worksheet is based on the mass-balance
method, and works by tracking and systematically accounting for all company
during the reporting year.
U.S. Department of Energy, Energy
Information Administration, “Voluntary Reporting of Greenhouse Gases 2004”,
Report #DOE/EIA-0608(2004), March 2006. Chapter 6: HFCs, PFCs, and Sulfur
In 2004, 33 entities reported
on 59 projects that reduced emissions of HFCs, PFCs, and SF6.
these projects claimed
direct reductions of SF6 emissions that totaled over 7 million metric
tons carbon dioxide equivalent. NOTE: EIA does not plan to produce a
full version of the 2005 annual report on the 1605b Voluntary Reporting of
Greenhouse Gases Program. Budget considerations and the need to develop
forms, instructions, and software under new guidelines prompted
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