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5.0 TRANSMISSION SYSTEM ACTIONS
Improvements in transmission system operations and transmission equipment efficiency can
reduce GHG emissions through a reduction in system losses. Decisions about investing in
transmission & distribution (T&D) systems affect how much of the power generated is
actually delivered to customers. Energy losses occur due to under-investment in T&D
infrastructure, inefficient operation and theft. While energy losses range widely, average
losses among 88 developing countries was greater than 18%, significantly higher than
average 5-10% losses of OECD countries.
Transmission capacity also affects the ability of utility systems to engage in power trading.
Some countries/regions experience transmission bottlenecks that prevent
regional/international power exchanges; this inhibits the use of existing generation capacity in
the system and may cause electricity shortages, because of the inability to transmit power
between areas with surplus power and power deficits. The environmental impacts of this may
vary it may lead to increased use of older, less efficient (and higher emitting) plants, and
may also lead to the construction of new units or individual back-up units to compensate for
the shortfall.
Transmission system reliability should be evaluated with regard to GHG emissions.
Consumers will adopt alternative energy strategies when transmission reliability is poor.
When alternatives include small generators powered by internal combustion engines, then
there will be a contribution to GHG emissions. This is especially the case when poor
transmission reliability results in nonpolluting generating capacity, such as hydropwer, being
replaced by internal combustion engines.
This section discusses some of the predominant transmission system actions being undertaken
in developing countries to improve system operations. Indications of the GHG effects are
provided when available; however, GHG effects are largely site-specific since they are
dependent on the fuels and technologies used to generate the electricity. USEA CC Mitigation Options Handbook
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5.1 HIGH VOLTAGE DIRECT CURRENT
CHARACTERISTICS
Most transmission lines use alternating current (AC), where the current direction typically
reverses itself 60 times per second. High Voltage Direct Current (HVDC) systems transmit
power using direct current, which flows in (only) one direction. 80% of the losses occurring
during transmission and distribution are due to resistance, which is inversely related to
voltagetherefore, the higher the voltage, the lower the T&D losses. Electrical resistance
losses in HVDC systems can be less than half of those in AC transmission lines, making
HVDC well-suited for bulk transfer of electricity over large distances.
With lower losses, less electricity generation is required. With lower generation, there is also
a reduction in GHG emissions when the transmitted electricity is generated by emitting
sources.
Experience with HVDC dates to 1954 when the first HVDC linewith a power rating of 20
MW and 1900 kV over a distance of 96 kmwas built in Sweden. Lines are now capable of
larger loadsBrazil has a 6,300 MW and 600 kV line that spans 800 km. Current world
HVDC capacity is approximately 63 GW, with plans for additional expansion underway.
New methods of power generation that generate in direct current (thermoelectric,
magnetohydrodynamic, fuel cells) will further improve the attractiveness of HVDC.
SIZE:
20 MW and 100 kV to 6,300 MW and 600 kV.
FEATURES
:
Overhead lines can extend more than 800 km. Cables can be
strung for more than 40 km. Transmission lines are perpetual,
but the lifetime of HVDC components (rectifiers, invertors,
thyristors and DC circuit breakers) is about 30 years.
COST
:
Total cost of HVDC systems includes conductors, insulators,
converters, tower and right-of-way costs. HVDC lines are less
expensive than AC, but require converters at each terminal.
HVDC is more economical than AC transmission for distances
over 500 km for overhead transmission lines; 20-50 km for
submarine cables; and 40-100 km for underground cables.
These break-even costs do not include any credit for avoided
emissions, or for avoided generation costs.
CURRENT USAGE:
In 1993, world HVDC capacity was 58,000 MW.
POTENTIAL USAGE:
An additional 9,000 MW planned (as of 1993).
ISSUES ASSOCIATED WITH IMPLEMENTING ACTION
There is a lack of industry familiarity with HVDC technology, and environmental criteria
are not well defined.

No DC circuit breaker exists, restricting DC use to point-to-point. Switching or fault USEA CC Mitigation Options Handbook
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clearing cannot be accomplished without total outage of all connected DC lines.
Back-to-back HVDC installations are needed to connect two alternating current
systems. Need further development of DC breakers to increase HVDC system flexibility
and development of lower cost converters at terminals.
HVDC does not create an electromagnetic field.
There is a limited ability to respond to large generator outages or system faults, resulting
in potential system instability.


CLIMATE CHANGE IMPACT

EMISSION EFFECT:


AVOIDED
OFFSET
REDUCED
CONDITIONS FOR EMISSIONS MITIGATION
:
Typical transmission line losses on the order of 7-10% in the United States and other
developed countries could be reduced to 3-5%, resulting in a corresponding reduction in
GHG-emitting generation demand. Transmission system line losses are often much higher
in developing countries, affording the opportunity for even greater reductions.

EMISSION ESTIMATE:
Because DC transmission is more efficient than AC, use of
HVDC reduces generation needed and the associated emissions
of greenhouse gases.

COST-EFFECTIVENESS:
N/A

SECONDARY EFFECTS
:
Use of more efficient DC transmission also minimizes associated
emissions avoided from electricity generation.


RESOURCES

Thallam, R.S. 1993. "High-Voltage Direct-Current Transmission," The Electrical
Engineering Handbook, Dorf, R.C. (ed.), CRC Press, Boca Raton, FL (US).
There is a partnership between the U.S. Department of Energy, (U.S.) Federal Marketing
Authorities, the Electric Power Research Institute, several electric utilities and equipment
manufacturers to develop and demonstrate HVDC. Projects have been conducted in the
following areas: the DC Pacific Intertie, New England/Hydro Quebec Line, and HVDC
Lines in the Mid-Continent Area Power Pool.
HVDC transmission lines are installed from Sardinia-Corsica-Italy, Greece-Crete, Zaire-
Egypt, Russia-Finland and Finland-Sweden, Brazil, India, and more.
An HVDC interconnection project between TNB of Malaysia and EGAT (Thailand) is
scheduled to be operational by mid 1999. With the development of the project, the
present 132/115 kV AC interconnection will be upgraded in terms of power capacity and
controllability which will further enhance system integrity, security and economic
interchange between the two parties.
An example transmission service agreement for the use of an HVDC line can be found on
the www at http://www.nees.com/oasis/hvdcts.htm.
The Electric Power Research Institute (EPRI) has and is developing HVDC support
equipment including a revenue meter and an HVDC transmission line reference handbook.



CONTACTS
a USEA CC Mitigation Options Handbook
Version 1.0 June 1999
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ABB Power T&D

Henry Chao

Raleigh, NC

Tel: (919) 856-2394

http://www.abb.se/pow/home.htm


Electric Power Research Institute

Mark Wilhelm

Director, Power Delivery Group

Palo Alto, CA

Tel: (650) 855-2771

mwilhelm@epri.com

http://www.epri.com/pdg/trans/


Electricit� de France

Alain Le Du

Paris, France

Tel: +33 1 47 65 33 88

Fax: +33 1 47 65 32 51

Alain.Ledu@edfgdf.fr



Harza Engineering

Peter Donalek

Electric Power Systems Department

Chicago, IL

Tel: (312) 831-3170

Fax: (312) 831-3999

pdonalek@harza.com

http://www.harza.com


Oak Ridge National Laboratory

Jim Van Coevening

Power Systems Technology Program

Energy Division

Oak Ridge, TN

Tel: (615) 574-4829

http://www.ornl.gov




USEA CC Mitigation Options Handbook
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5.2 IMPROVING LINE FLOW CONTROL


CHARACTERISTICS


Power electronics can be used to control the flow of electrical energy, making better
utilization of the transmission system possible, effectively increasing transmission capacity.


The Thyristor Controlled Series Capacitor (TCSC) uses advanced solid-state switches that
direct the flow of electric power more precisely along specific transmissio