1. 1 Local Area Planning Update to TRANSAC – July 29, 2015 Mitigation Update, Uncertainty Scenarios, and Next Steps

2. Mill Creek 161 kV Bus Outage – Mitigation complete –Impact of bus outage temporarily mitigated with new South Butte 230/161 kV tie in 2012. Rebuild of Mill Creek 161 kV bus was completed in 2014, alleviating the risk and consequences of a bus fault at this location. Billings Steam Plant 230 kV Bus Outage – reprioritized –Impact of bus fault temporarily mitigated with addition of two 230 kV circuit breakers to sectionalize bus for a bus fault in 2011. Additional mitigation planned for future with additional 230 kV breakers at Wicks Lane sub and an area 230/100 kV tie. With partial mitigation in place, problem is no longer a top 15 priority. Laurel – Bridger Auto 100 kV A & B Line Outage – reprioritized –Low voltage in area partially mitigated upon completion of new Columbus – Chrome 100 kV facilities. Other planned or in-service improvements defer any need for mitigation for ten years or more. 2 2012 – 2013 Study Plan Fixes Completed or Reprioritized

3. Rainbow Switchyard 69 kV Bus Outage – reprioritized –Partially mitigated with transfer of some 69 kV lines from Rainbow to Crooked Falls in 2014 – 2015; will be fully mitigated in 2016 when balance of 69 kV facilities at Crooked Falls transferred to Rainbow. Columbus-Rapelje – Alkali Creek 161 kV Line Outage – mitigation to be completed in 2015. –Mitigated with the installation of the new 230/100 kV auto bank at Columbus- Rapelje in 2015, and removal of the 161/100 kV tie at that location. Clyde Park 161/50 kV Auto Failure or Bus Fault – reprioritized –Mitigation plans remain same as published in 2012-2013 plan, but other projects now have higher priority. Spare transformer still on site. 3 2012 – 2013 Study Plan Fixes Completed or Reprioritized

4. Roundup Area Voltage Support (N-0) –Ranked #1 in current planning cycle, new problem. –Low voltage can occur in the Roundup area 50 and 69 kV transmission systems under summer peak conditions. –A total of 3 MVAR of distribution capacitors will be placed at Sumatra and Ivanhoe substations in 2016 to alleviate this condition. Columbus Area 50 and 100 kV System (N-1) –Ranked #2 in current planning cycle. –New 100 kV line route selection and easement acquisition in progress, and long with construction of Columbus-Rapelje 230/100 kV auto sub (to be completed in 2015). –Line route has moved to west on south end, and south end point has changed from Chrome Jct to Nye. Line construction planned for completion in 2017. 4 Mitigation for Highest Priority Problems in 2014-2015 Plan

5. Columbus Area 50 and 100 kV System (N-1) (continued) –Alternative stakeholder solution was considered and rejected. –Stakeholder suggestion would require immediate implementation of Phase 3 of Columbus area project (conversion of Chrome – Red Lodge – Bridger 50 kV system to 100 kV), which is not required for approximately 15+ years under current plan. Loss of Mill Creek – Deer Lodge – Montana Street 100 kV Line, or Mill Creek 100 kV bus fault –Ranked #3 in current planning cycle, new problem. –Loss of these facilities would cause the Anaconda City and Drummond 100/50 kV auto banks to overload and trip, leading to loss of Philipsburg and Anaconda City load. –Conversion of the Drummond – Anaconda 50 kV system to 100 kV will eliminate these weak links. Line is already designed and built for 100 kV operation; conversion of line and associated facilities scheduled for 2017. 5 Mitigation for Highest Priority Problems in 2014-2015 Plan

6. Loss of Missoula #4 to Hamilton Heights 161 kV lines (N-2) –Ranked #4 in current planning cycle. –Convert portions of the 69 kV system from Missoula to Hamilton to 161 kV; Add a 161/69 kV Switchyard at Stevensville. –Stevensville substation site selection complete, construction 2015 - 2016 –Missoula 4 – Stevensville line conversion now scheduled for completion in 2019. –Stevensville – Hamilton Heights 69 kV conversion 15+ years out. Loss of Broadview – Wicks 230 kV and Broadview – Alkali Creek 230 kV lines (N-2) –Ranked #5 in current planning cycle, identified late in previous cycle. –Loss of both of these lines causes low voltage in the Billings Area, leading to voltage collapse as the Billings area grows. 6 Mitigation for Highest Priority Problems in 2014-2015 Plan

7. Loss of Broadview – Wicks 230 kV and Broadview – Alkali Creek 230 kV lines (N-2) (continued) –This problem can be mitigated by installing a new 230 kV line from Broadview to Shorey Road with more capacity than NWE standard 230 kV construction. If siting and permitting issues arise, the new line can alternatively terminate at Columbus-Rapelje. –Due to the long lead time of building and permitting a new 230 kV line, a 40 to 50 MVAr synchronous condenser can be installed in the Billings area to assist with declining voltages for this contingency, until the new line can be constructed. This will also help keep voltage near normal operating range for this contingency after the new line is built. –Mitigation for this system problem also mitigates the following system problems: o Loss of Shorey Road – Alkali Creek 230 kV (System Problem #10) o N-1 Loss of Broadview – Wicks Lane 230 kV line OR Broadview – Alkali Creek 230 kV line (System Problem #13) 7 Mitigation for Highest Priority Problems in 2014-2015 Plan

8. East Helena 100 kV Bus Fault or Transformer Outage –Ranked #6 in current planning cycle. –Mitigation to solve this problem is a new 100/69 kV auto substation. In order to provide a 100 kV transmission source to this substation, a new 100 kV line will be built from Helena Valley sub and looped back to tie to an existing Helena Area 100 kV line from East Helena Switchyard. –Additionally to serve radial 69 kV load and generation out of East Helena and prevent 69 kV issues for an East Helena bus fault, breakers will be added to the 69 kV bus at East Helena, creating a breaker-and-a-half bus scheme. –Plan also accommodates a new distribution substation to serve load growth in Helena valley to north, and includes longer term provisions for switchyard at Canyon Ferry line taps. Loss of Ennis – Lone Mtn 69 kV Line or Ennis 161 kV Bus –Ranked #7 in current planning cycle. –Conversion of Jackrabbit to Big Sky 69 kV line to 161 kV in progress. Scheduled for completion in 2016. 8 Mitigation for Highest Priority Problems in 2014-2015 Plan

9. Rattlesnake 100 kV Straight Bus –Ranked #8 in current planning cycle. –Add a circuit breaker to split/sectionalize 100 kV bus during a bus fault, scheduled for 2017 or 2018. Loss of Great Falls Switchyard – MT Refining 100 kV Line –Ranked #9 in current planning cycle, new problem. –Loss of this facility can cause the Great Falls Switchyard – Riverview – GF Northwest 100 kV lines to overload and trip in the near future, leading to cascading outages in the area. –Reconductoring the overloaded facilities alleviates this problem; high temp conductor to be considered. Loss of Shorey Road – Alkali Creek 230 kV Line –Ranked #10 in current planning cycle, new problem. –Line loss overloads area 230/100 kV transformers in near future. –Mitigation for problem #5 alleviates this issue. 9 Mitigation for Highest Priority Problems in 2014-2015 Plan

10. Dillon-Salmon Bus Faults or Transformer Loss –Ranked #11 in current planning cycle. –Mitigation is near complete; new transformer is in service and most bus work is complete. Installation of second transformer and completion of bus work will occur in 2016. East Gallatin 161 kV Bus Outage –Ranked #12 in current planning cycle. –Bus has been resigned to accommodate a breaker-and-a-half scheme and one new 50 kV breaker, and transfer of distribution load to 161 kV. –With continued growth west of Bozeman and in the Belgrade area, current planning studies indicate installation of a new 161/50 kV auto in the Belgrade area should occur first; this auto alleviates problems associated with the loss of East Gallatin, and accommodates additional distribution needs in area. Scheduled for completion within five years, with East Gallatin rebuild to follow one to two years later. 10 Mitigation for Highest Priority Problems in 2014-2015 Plan

11. Loss of Broadview – Wicks 230 kV or Broadview – Alkali Creek 230 kV line (N-1) –Ranked #13 in current planning cycle, new problem. –Loss of one of these lines could overload the other. –Mitigation for problem #5 alleviates this issue. Loss of Great Falls Switchyard – Crooked Falls 100 kV Lines (N-2) –Ranked #14 in current planning cycle, new problem. –Loss of any two these three lines could cause the remaining line to overload and trip, causing cascading outages in the area. –Reconductoring these lines would alleviate the problem, but a more economical solution is under consideration: delayed line trip with generation runback to alleviate overload. 11 Mitigation for Highest Priority Problems in 2014-2015 Plan

12. Lower Duck Creek – Columbus Rapelje 161 kV Line or Big Timber 161/50 kV Auto Outage –Ranked #15 in current planning cycle. –Addition of 161 kV breakers (and auto bank upgrade) at Big Timber Auto mitigates problem. Scheduled for completion in 2019. All mitigation plans subject to change or modification as necessary to accommodate changes in load, generation, etc. QUESTIONS? 12 Mitigation for Highest Priority Problems in 2014-2015 Plan

13. Suggestions: High Wind System Wide –Existing Projects dispatched to capacity Loss of Thermal Plants –Heavy Imports, Heavy Summer Loss of Hydros –Extreme Winter Conditions Extreme Localized Growth Extreme Forest Fire impacts Other? Uncertainty Scenarios 13 Uncertainty Scenarios under consideration

14. Quarter 7 Run Uncertainty Scenarios Perform Reactive Resource Assessment Complete draft of “The Book” Quarter 8 Send out Draft of “The Book” for stakeholder review Conduct Public Meetings – Billings and Missoula Finalize “The Book” and close out the 2014/2015 Local Area Planning Cycle Next Steps 14

15. Questions? 15

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