National Electric Transmission Congestion Study - W2agz.com

Interconnection, and a strong commitment to identify
and implement sound solutions as quickly as
possible.
Seattle – Portland Congestion Area of
Concern
Electricity flows in the area near Highway I-5 from
Seattle south toward Portland have become increasingly
congested over the past two years, and there is
reason to believe that without attention, the problem
will grow worse. The Department highlights this
area as a matter of concern because these flows represent
a growing reliability problem for grid operators,
and an emerging economics problem for the
Northwest region.
Until recently, the states of Washington and Oregon
were winter-peaking—that is, electricity usage was
highest in the winter, due to a combination of electricity-based
home heating and a high proportion of
electricity-intensive industries. In recent years,
however, rapid population growth has led to higher
summer air conditioning loads, and economic
trends have shifted away from manufacturing and
toward a more service-based economy. As a result,
the region’s peak electricity demand now occurs in
the summer months. In the 1980s, western power
flows followed a predictable seasonal pattern—in
the summer, the Pacific Northwest delivered surplus
hydropower south to serve California’s peak
loads, while in the winter electricity producers in
California used their surplus generating capacity to
make electricity for shipment north to support Oregon
and Washington’s winter peak load. Today,
however, with the shift to summer peak loads, the
Pacific Northwest faces a growing need for more
transmission capacity to support market transactions
and protect system reliability. 52
operating limits are lower. 53 When these lines are
loaded above their limits—as occurred at least 29
times in August 2005—action is required to reduce
flow on the path, by redispatching production between
power plants until the overload is resolved. 54
NERC requirements for system security require that
such overloads be remedied within 30 minutes or
less. The magnitude of the overloads and the limited
range of solutions available to grid operators make
it increasingly challenging to operate the system
safely. In addition to thermal overloads, this congestion
could exacerbate voltage and transient stability
concerns.
At present, operators manage the congestion primarily
by adjusting generation output from Federal
hydro facilities at various locations north and south
of the Oregon-Washington border. However, if
more generation is built north of the border, southbound
flows will increase, making congestion
worse; unless the new generation is built south of
the border, or new transmission is built, operators
will eventually have to cut non-federal generation
or even black out some consumers to protect reliability.
Such actions would also cause somewhat
Figure 5-4. Congested Paths and Seasonal
Power Flows in the Pacific Northwest
In terms of real-time operations, some of the most
congested and problematic paths in the Northwest
cross the Washington-Oregon border. (See Figure
5-4.) The most serious problems occur in the summer,
when loads are highest and transmission
52 See comments by Seattle City Light, March 6, 2006, in response to DOE’s Notice of Inquiry of February 2, 2006.
53 When electricity flows through a line, some of the electricity is converted to heat; as ambient air temperatures rise, the line grows hotter because
less of the heat is dissipated into the air; as load on a transmission line increases, more electricity is converted to heat, the temperature of the line
increases, and the line sags lower. As a result, it is necessary to reduce permissible line loadings as ambient temperatures rise.
54 Bonneville Power Administration (BPA), “Challenge for the Northwest: Protecting and Managing an Increasingly Congested Transmission
System,” April 2006; BPA, “Congestion Schedule Management,” February 7, 2006.
U.S. Department of Energy / National Electric Transmission Congestion Study / 2006 47