Local Area Planning Update to TRANSAC – June 29, 2017 20pt Font – bold for presentation name, regular for date Local Area Planning Update to TRANSAC – June 29, 2017 Mitigation Update, Uncertainty Scenarios, and Next Steps

2014/2015 Study Plan Mitigation Update Roundup Area 50/69 kV Low Voltage (N-0) — Mitigation Complete Distribution capacitors added to the Sumatra and Ivanhoe 69 kV substations in 2016. Additional capacitors to be added to the Melstone 50 kV system in 2018. Mill Creek 100 kV Bus Fault (et al.) — Mitigation Complete Converted the 50 kV from Drummond – Philipsburg – Anaconda City to 100 kV in 2017. Ennis – Lone Mountain 69 kV Line — Mitigation Complete Completed conversion of the Jackrabbit – Meadow Village 69 kV to 161 kV in 2016. Dillon-Salmon 161 or 69 kV Bus Fault (et al.) — Mitigation Complete Rebuilt the 161 kV bus and added a 69 kV bus sectionalizing breaker. Upgraded both 161/69 kV autotransformers in 2015.

2014/2015 Study Plan Mitigation Update Rattlesnake 100 kV Bus Fault — Reprioritized Adding a sectionalizing breaker to the 100 kV bus is scheduled for 2018. Billings 230 kV Issues — Reprioritized Broadview – Wicks Lane <=> Alkali Creek 230 kV Lines (N-1) Shorey Road – Alkali Creek 230 kV Line Mitigation for the two above system conditions will be addressed as part of System Problem currently ranked #4. Lower Duck Creek – Big Timber Auto – Columbus-Rapelje 161 kV Line — Reprioritized Adding 161 kV line breakers at Big Timber Auto scheduled for 2018.

2016/2017 Study Plan Mitigation — Top 15 Rank Columbus-Rapelje – Columbus – Chrome Jct. 100 kV Line (N-1) ❶ Columbus-Rapelje 230/100 kV auto built in 2015. — Mitigation Complete New 100 kV line construction from Columbus-Rapelje – Nye Auto scheduled for completion in 2017. Billings – Laurel 100 kV Lines (2) (N-1) ❷ Build a 12-mile, 230 kV line from Baseline – Laurel Auto. Establish a 230/100 kV auto at Laurel Auto. Note: Mitigation required due to Customer Load Forecast increase. Missoula #4 – Hamilton Heights ‘A’ & ‘B’ 161 kV Lines (N-1-1) ❸ New Stevensville substation built in 2015/2016. — Mitigation Complete Add 12 MVAr of capacitors at Stevensville, scheduled for 2018. Convert portions of the 69 kV system from Missoula to Hamilton to 161 kV. Note: NWE has determined that a NERC corrective action plan is not required for this event; the unlikelihood of this event (which has never occurred) doesn’t justify the expense.

2016/2017 Study Plan Mitigation — Top 15 Rank Broadview – Wicks Lane <=> Alkali Creek 230 kV Lines (N-1-1) ❹ Build a new 20-25 mile, 230 kV line from Broadview – Shorey Road which provides route diversity from the two existing Broadview – Billings 230 kV lines. Merits: Serves as mitigation for lower-ranked Billings area system problems. Great Falls 100 kV Lines (12 combinations) (N-1-1) ❺ Establish an N-1 curtailment operating guide for the Great Falls area, which focuses on limiting non-firm transfers and South of Great Falls flows. Great Falls Swyd – Crooked Falls 100 kV Lines (2 of 3) (N-1-1) ❻ Establish a hydro run-back scheme as part of a curtailment operating guide for the Great Falls area.

2016/2017 Study Plan Mitigation — Top 15 Rank Great Falls Swyd – Montana Refining 100 kV Line (N-1) ❼ Reconductor two 100 kV lines with high-temp conductor: Great Falls Switchyard – Great Falls Riverview Great Falls Riverview – Great Falls Northwest East Helena 100/69 kV Autotransformer ≡ 100 kV Bus (N-1) ❽ Build a new substation (Custer Auto) to provide a second reliable 100 kV source to the Helena area 69 kV system. Construct a new 100 kV line from Custer Auto to both the Helena Valley and York Road (aka Lake Helena) substations. East Gallatin 161/50 kV Autotransformer ≡ 161 kV Bus (N-1) ❾ Build a new substation (Belgrade West) to provide another reliable 161 kV source to the Bozeman area 50 kV system. Merits: Joint effort with Distribution Planning as a new Belgrade distribution substation is needed, and off-loads a heavily loaded Trident Auto.

2016/2017 Study Plan Mitigation — Top 15 Rank Assiniboine 161/69 kV Autotransformer ≡ 161 kV Bus (N-1) ❿ Rebuild Assiniboine Substation to enhance reliability. Billings City 100 kV Lines (6 combinations) (N-1-1) ⓫ Convert Billings 8th Street – Laurel 50 kV to 100 kV. Build a five-mile 100 kV line from Shiloh to a new switchyard, tapping the converted Billings 8th Street – Laurel 100 kV line. Merits: Coordinated effort with Distribution Planning to establish a potential new distribution site. Missoula #4 – Bonner <=> Missoula #7 161 kV Lines (N-1-1) ⓬ Build a 10-15 mile, 161 kV line from Rattlesnake to Missoula #4. Note: NWE has determined that a NERC corrective action plan is not required for this event; the unlikelihood of this event (which has never occurred) doesn’t justify the expense at this time.

2016/2017 Study Plan Mitigation — Top 15 Rank Missoula City 100 kV Lines (4 combinations) (N-1-1) ⓭ Reconductor Reserve Street – City Sub #1 100 kV. Upgrade Miller Creek #4 161/100 kV autotransformer. Replace current-limiting device at Industrial Sub #3. Crooked Falls – Great Falls Northeast 100 kV Line (N-1) ⓮ Reconductor Montana Refining – City 100 kV with high-temp conductor. Billings Steamplant 230 kV Bus-Tie Breaker ⓯ Establish a pair of 230/100 kV autos at Rimrock. Merits: Serves as mitigation for lower-ranked Billings area system problems.

Uncertainty Scenarios Uncertainty Scenarios under consideration Suggestions: High Renewable Resources System-Wide Existing Projects dispatched to capacity Extreme Localized Growth 5-year summer peak load sensitivity case

Next Steps Quarter 7 Quarter 8 Run Uncertainty Scenarios Perform Reactive Resource Assessment (if deemed necessary) Complete draft of “The Book” Quarter 8 Send out Draft of “The Book” for stakeholder review Conduct Public Meetings – Butte and Helena Finalize “The Book” and close out the 2016/2017 Local Area Planning Cycle

Questions? Text, 60pt font, white

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