National Electric Transmission Congestion Study - W2agz.com

production by dispatching a fixed fleet of generation
to meet a known set of hourly electricity loads.
Both also take into account limitations on the ability
of the transmission system to support imports and
exports of power within the interconnection.
Loads
The WECC 2005 Load and Resources forecast was
the primary basis for load modeling. Existing and
predicted demand-side management is embedded in
area load forecasts, and transmission losses are included
in the load forecast as a fixed percentage of
each load. The Northwest Power and Conservation
Council’s models were used to determine loads for
Oregon, Washington and parts of Idaho. The California
Energy Commission’s September 2005 load
forecast was used to represent California loads.
Load forecasts for Colorado, Montana, Utah, Wyoming,
northern Nevada and parts of Idaho were
based on the RMATS September 2004 study, escalated
out to 2008 and 2015.
Transmission paths
The basic units of analysis for the study of congestion
in the Western Interconnection are the existing
catalogued major transmission paths defined by
WECC. The system’s historical patterns of power
flow, and the long history of coordination and information
sharing among western transmission planners
and operators have led to the identification of
67 major transmission paths. A path can represent
either a single transmission line or a combination of
lines from one area or combination of areas to another
area or combination of areas. A path may be
between control areas or internal to a control area. 17
Interactions between the power flows on various
transmission paths and resource output levels are
described by technical nomogram 18 relationships.
17 Recall that as directed by DOE, CRAI developed the functional equivalent of even more granular “paths” for the study of the Eastern
Interconnection by applying heuristic and statistical methods, essentially in a bottom-up fashion. By contrast, in the Western Interconnection, the
major transmission paths have already been defined on the basis of extensive planning studies and years of operating experience. They are
well-documented through a formal WECC process.
18 A nomogram is a graphic representation that depicts operating relationships between generation, load, voltage, or system stability in a defined
network. On lines where the relationship between variables does not change, a nomogram can be represented simply as a single transmission
interface limit; in many areas, the nomogram indicates that an increase in transfers into an area via one line will require a decrease in flows on
another line.
U.S. Department of Energy / National Electric Transmission Congestion Study / 2006 19