2009 Scenario Reliability Assessment - NERC

Scenario Reliability Self-Assessmentswith 100 percent confidence to produce their rated output at some coming hour since mechanicalfailures or other circumstances may limit their output to a lower level or even result in the plantbeing taken out of service. The probability that this would occur in the near term, however, islow.The Midwest ISO uses a centralized wind forecasting program in its market footprint to capturereliability and economic aspects of integrating wind into the day ahead and real-time markets.The forecast is based on the latitude and longitude of each wind farm and the hub heights of thewind turbines at that site. The real-time MW value is also provided to the wind forecast vendor.Each individual Commercial Pricing Node (CPN) is forecasted for each hour for the next sevendays. The program uses a Multi Numerical Weather Prediction (NWP) model to come up with itsbest estimate for each node, zone, Region, and Midwest ISO total.As wind penetration levels increase the forecast accuracy becomes essential to operate a reliablesystem. Additionally, accurate wind forecasts and timely updates are necessary in order toincorporate wind generation into the day-ahead market.As of the summer of 2008, the largest decrease in wind production for the Midwest ISOReliability Coordinator footprint was approximately 1,200 MW during a one-hour period.Because of the overall Midwest ISO system size compared to the size of this drop, the effectswere minimal. The Midwest ISO has not experienced an inability to meet demand due to a lackof wind production.(i) Operating Guides and Special Protection SystemsAlthough certain wind generation can provide counterflows in normally congested areas, moreoften there are challenges for the Midwest ISO Reliability Coordinator to manage this variablegeneration because much of it is being added as an Energy Resource and is utilizing availabletransmission capacity on a non-firm basis. Typically, transmission is constructed toaccommodate conventional generation capacity that can be dispatched and that capacity usuallycomes online after the transmission upgrades are made. Many owners of wind generation arealso financing upgrades to the transmission system, however, the generation usually gets builtfirst, and the transmission may follow months or years later. Often times a Special ProtectionSystem (SPS) is installed to automatically mitigate overloads. These SPSs and operating guidespresent operating challenges to the Midwest ISO Reliability Coordinator and to the systemoperators in the Region. Operators would need to implement operating guides quickly whichwould be a challenge with the increasing number of guides available.(j) Outage CoordinationAlthough accurate wind generation forecasts have been routinely achieved 24 to 48 hours out inthe future, wind cannot be forecast with any accuracy out two to three weeks, which is the timeframe required to assess transmission maintenance outages. Transmission maintenance outagesmay need to be evaluated with the worst-case assumptions regarding wind generation.(k) Congestion ManagementPresently wind generation is not fully integrated into the Midwest ISO market processes. Windgeneration is considered a self-scheduled resource that runs whenever the fuel source is present.Page 502009 Scenario Reliability Assessment