NTTG Economic Study and Biennial Study Update NTTG Economic Study and Biennial Study Update NTTG Study Cycle

2 Economic Study Request  There were three economic study requests submitted during NWE’s study request window which was from Jan 1, 2012 to Feb 28,  The three request were submitted by the following stakeholders.  1 request by Gaelectric  2 requests by NorthWestern  Information on all 3 requests could be found on NWE’s OASIS under “Transmission Planning – Economic Studies” section.  The 3 requests were accepted by NTTG as sub-regional request and agreed to consider those in their economic study process.  NTTG did not receive any other Economic Studies from other stakeholders.

3 Economic Study Request  The three studies were  Transmission to Northern California (Gaelectric)  Purpose: “To review the best means of building a transmission line within the NTTG footprint from the Great Falls, Montana area (Point of Receipt) to the Malin Substation (Point of Delivery), to carry approximately 1500 MW of renewable wind energy to the California Market by year end 2018.”  Only congestion analysis was requested by the submitter. Economic Benefit analysis was not requested.  Mountain States Transmission Intertie(MSTI) 500 kV Line (NWE)  Purpose: “MSTI will reduce the constraint between Montana and Idaho. The line is being proposed to help move renewable generation to markets such as Arizona, California, the Northwest, etc.”  Submitter directed NTTG to use this project in conjunction with other regional projects to alleviate congestion from Montana to Idaho for newer renewable resources in Montana trying to go to the markets in South.  500 kV Upgrade (NWE)  Purpose: “Respond to renewable generation development and Transmission Service Requests in Montana”  Submitter directed NTTG to use this project in conjunction with other regional projects to alleviate congestion from Montana to Northwest for newer renewable resources in Montana trying to go to the markets in West.

4 Base Cases Used for Economic Study Request   NTTG used two different scenario cases to study congestion for supplying 1500 MW of load at Malin from 1500 MW of resources in Great Falls Montana. » »Heavy Summer (Heavy load in NTTG footprint) » »Heavy Export (Heavy exports from NTTG footprint)   Other mitigations suggested by stakeholders to alleviate congestion. » »500 kV line from Townsend to Midpoint (MSTI) » »500 kV line from Hemingway to Captain Jack » »500 kV line from Midpoint to Hemingway.

5 Conclusions of Economic Study Request   Conclusions of the Study » »Heavy Summer Case: ♦ ♦ 1500 MW transfer can be accommodated in the base case (N-0) without adding any transmission upgrades. ♦ ♦ Possible because of the 30 Common Case Transmission Assumption (CCTA) facilities are included in the case. ♦ ♦ Contingency analysis results show that there are several line thermal overloads and numerous voltage violations that occur for various contingencies even with CCTA Projects. ♦ ♦ Additional transmission upgrades are needed and reactive support is also required at locations in Montana and Wyoming. ♦ ♦ Adding a 500 kV line from Townsend, Montana to Midpoint, Idaho (MSTI project) eliminates all of the significant violations in the heavy summer cases. The study results do not show a substantial improvement in adding the Hemingway to Captain Jack or Midpoint-Hemingway 500 kV lines for the summer load study. » »Heavy Export Case: ♦ ♦ 1500 MW transfer can be accomodated in the base case (N-0) only with upgrades to the Burns and Malin series capacitors even with the CCTA projects present in the base case. ♦ ♦ Contingency analysis results show the need to also upgrade the Garrison series capacitors or add transmission improvements beyond the 30 CCTA projects that are already included. ♦ ♦ Results show that adding a 500 kV line from Townsend, Montana to Midpoint, Idaho (MSTI project) reduces some voltage violations and eliminates the Garrison series capacitor overload, but overloads the Midpoint series capacitors in addition to the ones at Burns and Malin. The study results do show a substantial improvement in adding the Hemingway to Captain Jack and/or Midpoint-Hemingway 500 kV lines for the heavy export study. ♦ ♦ Series Capacitor upgrades at Burns, Malin and Midpoint along with a new 500 kV line from Townsend to Midpoint (MSTI) in lieu of the new 500 kV lines from Hemingway to Captain Jack or Midpoint to Hemingway produces acceptable results.

Economic Study Request Report and Results index.html 6

Economic Study Request Window   NWE’s Economic Study Request window is currently open until February 28,   NTTG Economic Study Request window is currently open until March 31, 2013   Interconnection Wide (WECC TEPPC) Economic Study Request window is currently open until January 31,2013.

8 Biennial Study Status Update   NTTG Technical Study group has performed the study work.   Study work included running contingencies on five different core cases. » »Heavy Summer » »Heavy Winter » »Heavy Export » »Heavy Import » »High COI-PDCI flow.   All cases had the CCTA project included in them.   The different CCTA Projects are shown in next slide.

Map of different CCTA projects 9

10 Biennial Study Status Update   NTTG also performed a Null Case study by removing the CCTA projects to determine if the existing system is adequate to handle the load of   NTTG currently in the process of reviewing the results and developing the final report.   The report should be out by the 1 st quarter of   NTTG also performing sensitivity analysis with the TransWest Express project as requested by the stakeholder.