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2009 State of the Market Report

Transmission Congestion

As in prior years, over two-thirds of real-time congestion occurred in the eastern half of the footprint. However congestion occurred more uniformly across the footprint in 2009 than in 2008. Congestion was down 10 percent in the East and 14 percent in the Central region, respectively, while it rose 50 percent (to $167 million) in the West due to increasing supply in that region (primarily wind resources). Transmission upgrades contributed to lower congestion into WUMS in 2009.

The figure also shows transmission constraints were binding more frequently in 2009, from 1.03 constraints per interval to 1.21. This is largely due to more low voltage constraints binding (partly as a result of uncontrollable wind generation in the West). The frequency of these constraints generally increased throughout the year.

To better identify the sources of congestion, Figure 55 shows the value of real-time congestion by type of constraint. This is computed in the same manner as the value of congestion in the previous analysis. For our analysis, we define four types of constraints:

  • Constraints internal to the Midwest ISO that are not coordinated with PJM. These are not market-to-market constraints and are labeled as “internal” constraints in our analysis;

  • The Midwest ISO constraints coordinated with PJM. These are labeled as Midwest ISO market-to-market constraints;

  • The PJM constraints coordinated with the Midwest ISO. These are labeled as PJM market-to-market constraints; and

  • Constraints located on other systems that the Midwest ISO must redispatch to relieve when Transmission Loading Relief (“TLR”) is requested. These are referred to as “external” constraints in our analysis. Congestion occurs on external constraints when a TLR is called on a neighboring system that causes Midwest ISO to re-dispatch its generation.

As in prior years, most of the congestion in 2009 occurred on Midwest ISO-managed constraints (internal and Midwest ISO market-to-market constraints), which represent over 90 percent of the total congestion value. Of this congestion on the Midwest ISO system, over 40 percent occurred on market-to-market constraints. Although relatively few constraints are coordinated under the market-to-market process, those constraints are some of the most valuable on the Midwest ISO system. The top five constraints alone comprised 61 percent of all market-to-market congestion

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