National Electric Transmission Congestion Study - W2agz.com

As shown in Figure 3-6, major constraints within
the Entergy portion of the SERC 21 area are limiting
flows from Missouri to Arkansas, Central to South
Arkansas, flows into the SPP system (Arkansas to
Oklahoma), flows from Alabama to Mississippi,
and—until recently—flows into New Orleans.
Tennessee Valley Authority (TVA)
7. Volunteer Transformer Bank and Sullivan
Transformer Bank (now upgraded)
8. Cumberland-Davidson and Johnsonville-
Davidson
9. Tennessee to Georgia
In the TVA area, the most limited flow directions
are Tennessee to Georgia (Chattanooga-Huntsville
to Atlanta), West to Central Tennessee (flows between
Cumberland Fossil Plant and Nashville) and
Tennessee to Kentucky (mostly flows from
Cumberland into the LGEE system in Kentucky).
Southern Company and VACAR (non-
Dominion)
10. Southeast into Florida
11. Eastern South Carolina
12. Atlanta
Problems in the Southern area reflect import limitations
into Atlanta and limited flows from Georgia to
Florida (limited by constraints on the Florida end).
Congestion problems in the VACAR (non-
Dominion) portion of SERC are largely concentrated
around Charleston, South Carolina.
3.2. Results from Simulations
of the Eastern
Interconnection
Interpreting the modeling results
Electric system simulation modeling is performed
for many purposes, including valuation of existing
or proposed generation or transmission assets,
long-range system planning, forecasting of electricity
prices or transmission congestion contracts, or
cost-benefit studies to assess regulatory reforms or
market re-design options. For all these purposes, it
is necessary to validate the data, modeling assumptions
and simulation algorithms. The validation approach
varies depending on the goal or purpose of
the modeling. In most cases, modelers focus on how
realistically the simulation results reflect historically
observed inter-regional flows of power and
whether the simulated patterns of congestion are
similar to those observed in real systems.
In this study, the process of model validation particularly
focused on comparing simulated patterns of
congestion against those historically observed.
Thus, while the model calculates and optimizes
electricity production costs subject to reliability
constraints, it has been validated for transmission
metrics—flows, limits, and congestion results—
rather than power production costs. The congestion
modeling process followed an iterative approach in
which congestion results were benchmarked
against validated data, the differences were closely
examined, assumptions were revisited and input
data verified until discrepancies were ultimately resolved
or understood.
This is the first interconnection-wide study of eastern
congestion. There are certain questions about
data quality and modeling effectiveness—particularly
with respect to reactive power, reliability limits
and treatment of line losses—that merit further
examination. With those uncertainties in mind, the
absolute values of congestion metrics for each
transmission path or constraint are less important
than their relative weights. The goal here has been
to identify those paths and areas that are especially
congested, not to calibrate exactly how congested
each area is now or may become. The Department
of Energy is responsible for identifying areas where
congestion is now or is likely to become especially
severe, and if appropriate, facilitating mitigation of
such problems through the designation of National
Corridors. For that purpose, determining the relative
rankings of the congestion associated with specific
constraints is a very useful model result. By
contrast, the estimates of power production costs
should not be regarded as valid predictors for the
21 The SERC Reliability Corporation (SERC) is the Regional Reliability Organization (RRO) responsible for promoting, coordinating and
ensuring the reliability and adequacy of the bulk power supply systems in the Southeast, excluding Florida.
U.S. Department of Energy / National Electric Transmission Congestion Study / 2006 25