National Electric Transmission Congestion Study - W2agz.com

on a line designed specifically for delivery of the
plants’ output to loads, so high loading for this line
demonstrates desirable asset utilization, not undesirably
high congestion. Many of the most heavily
loaded lines in this period were other major tie-lines
similarly designed to facilitate high-volume bulk
power trades (Northwest to Canada northbound, Alberta
west to British Columbia, the Pacific Direct
Current Intertie, the California-Oregon AC Intertie,
and the westbound line from Four Corners.
4.2. Congestion Findings From
Modeling for the Western
Interconnection
Figure 4-4 shows how projected relative congestion
patterns vary as a function of fuel prices. This graph
orders the most heavily used transmission paths (as
measured by U90, the number of hours when usage
equals or exceeds 90% of the line’s limit), at the
base case price for gas ($7/mmBtu). For each path,
the graph also shows projected U90 hours for lowand
high-case fuel prices as well. The shifts in usage
between paths as fuel prices change reflects how
electricity flows change with fuel prices—when gas
prices are low, long-distance coal-by-wire imports
are somewhat less competitive, but when gas prices
rise, load-serving entities buy more coal, nuclear
and hydropower (to the degree that they are available)
and reduce purchases from gas-fired power
plants. The shifts in relative congestion associated
with fuel price changes would be even more pronounced
in a low-hydro scenario.
In its modeling, the western analysis sorted the congested
paths by a number of methods to identify
those that were most congested. Using an averaging
method that combined both usage and economic
impact, they found the following paths were the
Figure 4-3. Most Heavily Loaded Transmission
Paths in 2004-2005
Based on values for U90.
Figure 4-4. Projected Congestion on Western Transmission Paths, 2008
U90 values at alternative natural gas prices.
34 U.S. Department of Energy / National Electric Transmission Congestion Study / 2006