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2009 State of the Market Report

Transmission Congestion

facility by economically redispatching generation. However, external entities contribute to the flows over the constrained internal transmission facilities. Hence, the Midwest ISO invokes a TLR procedure to ensure that the external parties contribute to reducing the flow over the constrained facility. As we have shown in previous reports, the TLR process is a much less efficient and a less controllable means to manage congestion than economically redispatching generation through LMP markets. This less efficient process leads to:

  • More than three times the curtailments to manage congestion on average than the

quantity of economic redispatch needed; and

  • Less timely and accurate control of the system, resulting in lower reliability.

LMP markets help to efficiently manage most internal congestion through redispatch rather than the curtailment of scheduled transactions through the TLR process. Figure 56 shows TLR activity on Midwest ISO flowgates on an annual basis from 2007 to 2009 and monthly basis for 2008-2009.

Figure 56: Monthly TLR Activity 2007 – 2009

1,500

300

200

100

0

GWh Curtailed

Hours of TLRs

1,250

1,000

750

500

250

Level 5 Level 4 Level 3b Level 3a

0

07 08 09 J F M A M J J A S O N D J F M A M J J A S O N D

2008

2009

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