2009 State of the Market Report
market power mitigation. The three NCAs currently defined are the Minnesota NCA, the WUMS NCA, and the North WUMS NCA.
Market power associated with non-NCA constraints can still be severe. If the constraints are not chronic, however, they generally raise less competitive concerns. Due to the vast number of potential constraints and the fact that the topology of the transmission network can change significantly when outages occur, it is neither feasible nor desirable to define all possible BCAs in advance. Therefore, BCAs are defined dynamically when non-NCA constraints bind on the transmission network. A BCA includes all of the generating units that have a significant impact on the power flows over a constrained interface. Figure 74 shows the portion of active NCA and BCA constraints that have at least one pivotal supplier.
Figure 74: Percentage of Active Constraints with a Pivotal Supplier 2009
Share of Constraints with a Pivotal Supplier
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
BCA Constraints WUMS NCA Constraints Minn NCA Constraints
In most months of 2009, active constraints in each of the constrained areas had a pivotal supplier in the majority of hours. During the year, 69 percent of the active NCA constraints into WUMS had a pivotal supplier, down from 79 percent in 2008. During each of the three summer months, however, this percentage exceeded 80 percent. For the Minnesota NCA, 75 percent of active constraints had a pivotal supplier, up from 69 percent in 2008. For BCA constraints, 64 percent