Next Limiting Element Study

This study was last conducted for the 2018 Assessment. Since that time, numerous generator queue requests within and outside the ATC system have made an update of questionable value. ATC continues to participate in the MISO assessments of generation requests. The results of the update for the 2018 Assessment are still shown below.

The main objective for this study was to determine what thermal limitations, beyond those being addressed with the 2018 10-Year Assessment project list, ATC might see with high biases across the ATC transmission system.

The base model for the study was the 2028 all-project shoulder from the 2018 10-Year Assessment. Nine different biases were applied to the model and then no load loss allowed contingencies were applied. No load loss allowed refers to NERC TPL-001-4, Table 1 requirements to not interrupt firm commitments or lose non-consequential load for specific categories of Planning contingencies. ATC also applied similar contingency categories to its non-BES facilities. SPS/RAS operation and voltage limitations were not considered in the study. The nine different biases were:

  • Minnesota to ATC
  • Minnesota to Illinois and Indiana
  • Iowa to ATC
  • Iowa to Illinois and Indiana
  • Minnesota and Iowa to ATC
  • Minnesota and Iowa to Illinois and Indiana
  • Illinois and Indiana to ATC
  • Illinois and Indiana to Minnesota
  • Illinois and Indiana to Minnesota and Iowa

The study showed several facilities within the ATC system could be limitations under high bias scenarios. The first and second limitations for each bias scenario is shown in table 1.

Table 1: ATC First and Second Limitations for Each Bias Scenario

Bias ScenarioATC First Limiting ElementATC Planning ZoneATC Second Limiting ElementATC Planning Zone
Minnesota to ATCPetenwell – Saratoga 138-kV line X-431Arpin – Sigel 138-kV line X-331
Minnesota to Illinois and IndianaArpin – Sigel 138-kV line X-331NoneN/A
Iowa to ATCPetenwell – Saratoga 138-kV line X-431Eden – Spring Green 138-kV line X-173
Iowa to Illinois and IndianaPetenwell – Saratoga 138-kV line X-431Eden – Spring Green 138-kV line X-173
Minnesota and Iowa to ATCPetenwell – Saratoga 138-kV line X-431Eden – Spring Green 138-kV line X-173
Minnesota and Iowa to Illinois and IndianaPetenwell – Saratoga 138-kV line X-431Arpin – Sigel 138-kV line X-331
Illinois and Indiana to ATCNoneN/ANoneN/A
Illinois and Indiana to MinnesotaFox River - North Appleton 345-kV line NAPL1214Point Beach - Kewaunee 345-kV line Q-3034
Illinois and Indiana to Minnesota and IowaFox River - North Appleton 345-kV line NAPL1214Point Beach - Kewaunee 345-kV line Q-3034

The study was informational only and no projects to fix the thermal limitations above, or other thermal limitations found in the study, will be proposed in this Assessment. ATC continues to monitor the limitations identified by this study.