&EPA
United States
Environmental Protection
Agency
The SF6 Emission Ream
Partnership for Ele<
Power Systems is a voli
program between the
Environmental Protecti
power companies. Its g<
to identify and implemi
cost-effective operational
and technical solutions
to reduce SF6 emissir
By reducing SF6 emissio
where feasible, the elec
power industry can pla
a key role in addre
climate change. Th
Partnership is one c
EPA voluntary prog
working with specit
industries that emit potent
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Equipment Upgrades and Preventive
Maintenance Improve Performance
and Reduce SF. Emissions
\\CTransmission Case Study
\JCTransmission is the nation's first fully independent electricity
transmission company. With a service territory of approximately
7,600 square miles, the company delivers electricity to nearly
4.9 million people in southeastern Michigan. The company is
focusing on enhancing operation, maintenance, and investment
in its transmission infrastructure. As an important step toward
improved operation, \JCTransmission recently implemented
several initiatives that reduced sulfur hexafluoride (SF6)
emissions by 79 percent within a two-year period, and in the
process, also reduced annual expenditures to replace and
manage SF6 gas losses.
Company Profile
In April 2004, YTCTransmission became the first, fully independent electricity
transmission company in the United States, following the transfer of ownership
from DTE Energy to its parent company, ITC Holdings Corp. YTCTransmission
owns a fully regulated, high-voltage system that transmits electricity to local
electricity distribution facilities. The company currently serves a population
of approximately 4.9 million throughout 13 southeastern Michigan counties,
including the Detroit metropolitan area. With the combined service areas of
YTCTransmission and Michigan Electric Transmission Company, LLC (METC),
ITC Holdings Corp. is operating the largest transmission system in Michigan's
Lower Peninsula. Additionally, on December 20, 2007, ITC Midwest LLC,
a subsidiary of ITC, completed the acquisition of the transmission assets of
Interstate Power and Light Company (ILP), a subsidiary of Alliant Energy
Corporation. The transaction included the purchase of 6,800 miles of IPL
transmission lines at voltages of 34.5 kilovolts and above, and 170 stations and
substations in portions of Iowa, Minnesota, Illinois, and Missouri.
Seeking to improve its operations, YTCTransmission is exploring opportunities
to enhance the transmission system's integrity and reliability. In 2007 the
company joined the U.S. Environmental Protection Agency's (EPA) SF6
Emission Reduction Partnership for Electric Power Systems. The Partnership is
a voluntary program between government and electric utilities with a focus on
developing and implementing cost-effective operational and technical solutions
to reduce SF6 emissions and improve SF6 handling and maintenance.
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Benefits of Joining the Partnership
\TCTransmission joined the SF6 Emission
Reduction Partnership for four reasons:
• To institute an industry standard for
reporting of emissions and inventory
tracking, resulting in reduced SF6 gas
purchases and related cost savings;
• To implement best practices in SF6 gas
handling, resulting in emissions
ate with other utility Partners
.,, in developing and improving
idustry best practices in SF6 gas handling
and maintenance; and
• To be recognized nationally for efforts and
successes in reducing greenhouse
Initiatives to Reduce SF6 Emissions
\JCTransmission is reducing its SF6 gas
emissions through two key programs: (1)
an infrastructure improvement program,
which addresses equipment replacement,
and (2) a preventive maintenance
program, which targets equipment
repair. \JCTransmission has made a
strong commitment to reduce emissions
by accelerating the repair and, when
appropriate, early retirement of leaky
equipment. Tracking the costs associated
with repair operations including
replacement gas and labor, as well as
the costs associated with installing new
equipment, facilitates decision-making.1
1. Infrastructure Improvement Program
The utility's infrastructure improvement program
consists of two equipment replacement projects,
targeting circuit breakers and gas insulated
switchgear (GIS).
1 With the recent acquisition of METC by ITC Holdings Corp., the SFe
emission reduction initiatives implemented by TTCTmnsmission are begin-
ning to be implemented by METC.
2 Typical circuit breakers to be replaced include: Westinghouse 145SF /
3450-SF; General Electric ATB-362-7Y, 7, and 5; and ITE 230-GA20-20B /
242GA-40-20C / 145GA-30-20C / 145GA-63-20C / Delle Alsthom FB-2A.
3 Regarding outdoor circuit breakers, there is an agreement between the
supplier and the utility that the breaker will maintain a maximum permis-
sible leak rate of 1 percent per year, otherwise the breaker will be repaired
for free by the supplier.
Circuit Breaker Replacement Project
YTCTransmission has an ongoing circuit breaker
replacement project that began in 2003. Under
this project, the utility tracks the frequency of
maintenance of its gas breakers to help prioritize
which ones should be replaced. In making the
decision to replace equipment, maintenance costs
and performance records of leaking breakers are
reviewed and compared to the costs to replace the
breakers. The utility also considers other benefits
associated with new breakers, such as greater
equipment reliability. To date, the company has
selected variations of SFMT models supplied by
Mitsubishi Electric as its equipment replacements,
chosen in part due to their quality of design and
leak-tight construction.2 The Mitsubishi SFMT
models have low gas leak rates, from 0.1 percent
to 1 percent per year.3
Since beginning the circuit breaker replacement
project, YTCTransmission has replaced or
decommissioned 57 leaking circuit breakers,
varying in size and designed for 120 kV to
345 kV transmission systems with a vintage
range from 1964 to 1982. With the new circuit
breakers installed, the manufacturer conducts
periodic checks to verify that gas system pressure,
quality, and moisture are normal. In the event of
a low-pressure alarm signal, the manufacturer
investigates any evidence of leaks under
warranty. As a result of these replacement efforts,
YTCTransmission reduced its SF6 gas emissions and
continues to operate the successful replacement
program. To date, no detectable SF6 leaks from
newly replaced equipment have occurred.
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Gas-filled
free-standing CT
GIS Infrastructure Replacement Project
The second major project in the Infrastructure
Improvement Program focuses on replacement of
GIS. The utility's transmission system acquired
four in-service GIS sites manufactured between
1970 and 1972: St. Antome (ITE), Camff
(Delle Alsthom-Cogenel), Midtown (Delle
Alsthom-Cogenel), and Cato (Delle Alsthom-
Cogenel). Following the transfer of ownership
and commencement of independent operation
in 2004, YTCTransmission determined that these
substations were a significant source of SF6
emissions. The leaks and intensive maintenance
required for each site prompted the decision to
replace the aging GIS with newer equipment.
In 2005, the utility initiated a plan to replace
these installations over a period of four to six
years. The maintenance-prone, dual-pressure gas
circuit breakers at the St. Antoine facility were of
particular concern, and, therefore, this site was
targeted first.
By the second quarter of 2007, equipment in
the St. Antoine and Caniff substations had
been replaced with new equipment supplied
by Mitsubishi Electric that has a combined SF6
nameplate capacity of 8,050 pounds.4 Workers
recovered the gas remaining in the replaced
GIS, verified that the gas met acceptable criteria
for reuse, and then returned the recovered gas
to YTCTransmission's inventory for future use.
4 The written commercial contract stipulates the replacement GIS has a leak
rate of less than 0.1 percent per year and if it fails to meet these specifica-
tions it must be repaired for free by the supplier.
Continued on last page.
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A total of 25 bottles or 2,875 pounds of SF6
gas was recovered and added to inventory.
The Midtown and Cato substations, with
a combined SF6 nameplate capacity of
5,000 pounds, have replacement pending.
The GIS replacement project at the St. Antoine
(ITE) site alone enabled the company to
eliminate approximately 104 man-hours of
labor in the winter and 24 man-hours in
the summer. Additionally, the company has
eliminated the need to purchase approximately
16 cylinders of SF6 gas annually (about
1,840 pounds) to replace losses from the
leaking equipment.
2. Preventive Maintenance Program
TTCTransmission's equipment replacement
programs are complemented by an aggressive
maintenance plan launched in 2004, which
includes repairing leaks in equipment not ready
for replacement. TYCTransmission's workforce
has since taken on a number of repairs
including installing bolted-on clamp/seal rings
around leaking gas breaker bushings, repairing
gas breaker tube fittings, replacing seals at
interrupter flanges, and replacing leaking
underground pothead flange valves. Generally
these repairs are being made on equipment
manufactured between the 1970s and 1990s.
Leak Detection Practices
Leaks are first identified using the low-gas
density alarm included with the circuit breaker.
A work request is subsequently issued to
personnel to locate the leak source and repair
it, thus avoiding future refill visits and the
associated costs. \TCTransmission field personnel
locate the leaks using commercially available
and inexpensive electronic leak detectors (CPS
brand refrigerant leak detector. Model LS790B)
and a solution (Snoop liquid leak detector)
that forms bubbles upon pinpointing a leak
source. This solution is especially suited for
cold weather, when many leaks increase due to
cold-induced contraction. \TCTransmission pays
particular attention to the potential for gas
leaks from the new equipment installed since
2003, for which leaks should be minimal.
For more information on
the SF6 Partnership go to:
www.epa.gov/electricpower-sf6
June 2008
Company Achievements
Through the initiatives described
above, \JCTransmission is implementing
industrial best practices and maintenance
techniques in handling SF6 gas into its
standard operating procedures—achieving
significant emissions reductions and
operational efficiencies.
• In 2005, the first full year for which the utility
tracked its SF6 gas emissions, YTCTransmission
calculated a total annual emissions estimate
of 13,725 pounds, using EPA's recommended
mass-balance method. In 2006, the utility
calculated 6,546 pounds of annual emissions—
an impressive emissions reduction of 52 percent.
This significent reduction is largely due to the
replacement of leaking equipment and the
aggressive preventive maintenance program.
• In 2007, YTCTransmission further reduced
SF6 emissions to 5,745 pounds, representing a
58 percent reduction from baseline SF6 emissions.
• With standard reporting and inventory tracking,
YTCTransmission is now able to identify and
forecast SF6 gas requirements, facilitating cost
savings on SF6 purchases. As a direct result
of its efforts, YTCTransmission reduced the
need to purchase SF6 from gas suppliers as
YTCTransmission's reliance on its own
inventory increased.
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