September 18, 2007 Regional Disturbance PSERC Project Proposal

Event Summary Violent storms moving through the Dakotas and Minnesota early on September 18 forced numerous transmission lines (mainly 345 kV) out of service. As a result, at about 6:20 am EDT, a large portion of the western Midwest Independent Transmission System Operator (MISO) system along with systems in Manitoba and Saskatchewan separated electrically from the rest of the Eastern Interconnection. MISO was able to restore the U.S. section of the grid within 10 minutes, and remained in conservative operation until the grid was stabilized and secure as a precaution. Saskatchewan Power also separated from the Eastern Interconnection when it lost its 230 kV tie lines into Manitoba and North Dakota. Generation outages totaling 896 MW occurred as well, resulting in customer outages. Saskatchewan Power reconnected to grid within an hour, and almost all customer load was restored within 2 hours.

Rough Sketch of Island

Challenges in Real Time Operations There is a need to identify current system margin from transient instability following a disturbance/fault: Current On-Line Transient Stability Assessment typically is setup where: A real time snapshot is taken from State Estimator The State Estimator Solution is solved in an off-line powerflow application And then transient stability analysis is performed using off line software such as PSS/E Dynamic or Power Tech TSAT for given fault scenarios. This approach requires large detailed modeling data for generators, load, and relays. This approach requires “scenario of faults” are pre-determined. This approach can also be time consuming and not viable in the real time operations

Challenges in Real Time Operations Detail Challenges in the model: MISO has a large EMS model that encompass almost all Eastern Interconnection. Creating a conventional dynamic model is not practical. The previously mentioned approach would require a good method of equivalencing. Challenges in determining fault scenario (i.e. Fault Screening): In the Sep 18 event, N-2 contingencies are the initiators of the event. The two line trips do not share any commonality (i.e. they are not common towers, not common breakers, not common right of way, etc)