Local Area Planning Update to TRANSAC – December 21, 2016 20pt Font – bold for presentation name, regular for date Local Area Planning Update to TRANSAC – December 21, 2016

Status Update Analysis of Future Cases Base cases representing the peak scenarios over the 5, 10, and 15 year planning horizon have been completed, along with System Normal and Contingency case powerflow simulations. Problems identified and reported in the “State-of-the-System” study are not mentioned in this presentation, if they continue to exist. Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Substation Projects included in 2021-2031 base cases: Crooked Falls Expansion/Rainbow removal Alkali Creek Sub upgrade (tie in adjacent line) Rimrock Sub rebuild (Major rebuild, 2 230/100 kV auto transformers) East Gallatin Sub rebuild (bus reconfiguration) Big Timber Auto upgrade (new line breakers, transformer) Livingston Sub rebuild (combine subs, added capacitors) Belgrade West Sub (new sub, 161/50 kV auto transformer) Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Substation Projects included in 2021-2031 base cases: York Switchyard (new sub, added line breakers) Custer Auto (new sub, 100/69 kV auto transformer) East Helena (minor bus reconfiguration) Great Falls 230 Switchyard (minor bus reconfiguration) Kershaw Switchyard (new sub, added line breakers, capacitor) Rattlesnake Switchyard (100 kV bus tie breaker added) Stevensville Capacitor Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Substation Projects included in 2021-2031 base cases: Line breakers added to the following substations: Sheridan Auto 161 kV breakers King Ave 100 kV breakers Wicks Lane 230 kV breakers Missoula #5 100 kV Breakers Target Range 161 kV Breakers (installed 2016) Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Transmission Projects included in 2021-2031 base cases: Anaconda – Drummond 100 kV upgrade from 50 kV GF 230 Swyd – Riverview – GF Northwest 100 kV conductor upgrade Baseline – Meridian 100 kV conductor upgrade Rapelje – Nye 100 kV line (new) Broadview – Billings 230 kV line (new) Big Timber Auto – Melville 50 kV conductor upgrade Livingston – Emigrant 69 kV conductor upgrade Holter – Helena Valley 100 kV conductor upgrade Helena Valley 100 kV Loop (new) Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Customer Forecast Projects in 2021-2031 base cases: Great Falls Eastside rebuild New Cenex 100 kV substation Cenex Lines – conductor upgrade Jackrabbit 161 kV distribution transformer Lone Mountain 161 kV distribution transformer Includes 69 kV to 161 kV Ennis – Lone Mountain cutover New Big Sky area 69 kV substation New Helena Valley area 100 kV substation Colstrip Units 1 & 2 Shutdown Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Summary Results 2021 – 2031 Cases: Thermal Issues (P0) No thermal overloads were observed under normal system conditions. (P12) GF Southeast – GF Northeast 100 kV overloads, automatic tripping results in cascading overloads & loss of multiple Great Falls substations. (15-year Planning Horizon) (P12/P13/P23) Steamplant 230/100 kV autos overload in 5-year planning horizon, Rimrock Project mitigates. (P12/P23) Steamplant – Laurel 100 kV or Baseline – Laurel 100 kV overloads, automatic tripping results in loss of Laurel substations. (15-year Planning Horizon, due to customer forecasted growth) (P12/P13/P22) Rimrock – Eastside 100 kV overloads, automatic tripping does not result in cascading overloads. No loss of load. (10- year planning horizon, shift in 100 kV flow from Rimrock Project) Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Summary Results 2021 – 2031 Cases: Thermal Issues (P12/P23) York Swyd – East Helena Swyd 100 kV “A” or “B” overload, automatic tripping results in cascading overloads & loss of multiple Helena substations. (5-year planning horizon, Custer Auto project mitigates) (P12) Hamilton City – Hamilton Southside 69 kV overloads, automatic tripping results in loss of Hamilton and Darby substations. Radial configuration, mitigation plan developed. (15-year planning horizon) (P13/P23) Hamilton Heights – Corvallis 69 kV overloads, automatic tripping results in cascading overloads & loss of multiple Bitterroot area substations. (5-year planning horizon) (P24) Rattlesnake Swyd – Reserve St 161 kV overloads due to current limiting device. (15-year planning horizon) Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Summary Results 2021 – 2031 Cases: Thermal Issues (P24) Reserve St – Missoula #1 100 kV overloads, automatic tripping results in further overloads. No loss of load. (10-year planning horizon) (P23) Hamilton Heights 161/69 kV ‘B’ transformer, automatic tripping results in loss of all Bitterroot area 69 kV substations. (5-year planning horizon, load loss allowed by TPL standard). (E2B) Hardin Auto – Crossover 230 kV overloads in 5-year planning horizon, New Broadview – Billings 230 kV line mitigates. (E2B) GF City – MT Refining 100 kV overloads, automatic tripping results in cascading overloads & loss of multiple Great Falls substations. (10-year Planning Horizon) (E2B) Missoula #4 – Stevensville 69 kV ‘A’ & ‘B’ lines, automatic tripping results loss of all Bitterroot 69 kV substations. (load loss allowed by TPL standard). Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Summary Results 2021 – 2031 Cases: Voltage Issues (P0) Roundup - Musselshell 50 kV line, minor low voltage in 5-year planning horizon and declining into major low voltage in the 10-year and 15-year planning horizons. (P0) Sheridan – Dillon 69 kV line, minor low voltage starting in the 15- year planning horizons. (P1) All voltage deviation violations also resulted in low voltage violations. (P12) Bozeman Division 161 kV system, minor low voltage starting in the 15-year planning horizon. (P12/P13) Laurel Area – 100 kV & 50 kV, minor low voltage starting in the 10-year planning horizon. Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Summary Results 2021 – 2031 Cases: Voltage Issues (P13/P22) Lewistown District, major low voltage spread across 50 kV system and declining (minor low voltage now). Minor low voltage on 100 kV system (5-year planning horizon). (P13/P22/P23) Roundup area 100 kV, moderage low voltage in the 5- year planning horizon and declining into major low voltage in the 10- year and 15-year planning horizons. (P13) Stevensville 69 kV area, minor low voltage in the 5-year planning horizon and declining into major low voltage in the 10-year and 15-year planning horizons. (P13) Havre City 69 kV system, minor low voltage in 5-year planning horizon and declining into moderate low voltage in the 10-year and 15-year planning horizons. Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Summary Results 2021 – 2031 Cases: Voltage Issues (P22) Garrison (BPA) 230 kV Bus Fault causes widespread minor to moderate low voltage across multiple divisions in the 10-year planning horizon and declining into major low voltage in the 15-year planning horizon. (P22) Big Timber 50 kV area, minor low voltage in the 10-year planning horizon. (E2B) Greater Billings 230 kV, 161 kV, 100 kV, 50 kV system, minor low voltage in 5-year planning horizon, New Broadview – Billings 230 kV line mitigates. Title, 24pt font, bold, white Body Copy/Bulleted Text, 22pt font, black (adjust as necessary)

Analysis of Future Cases Pending Analysis to be Completed: P3 and P6 events (N-1-1) power-flow simulations are near completion. Massive data set to analyze. Corrective action allowed between element outages. Stability (Dynamic) simulations have be started and will be completed soon. No major problems are anticipated.

Next Steps Next Steps Verify New Problems Found. Prioritize Problems using Decision Rules. Begin or Continue Mitigation Studies.

Questions? Text, 60pt font, white

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