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Local Area Study

Local Area Study. Mitigation of High Priority System Problems 2012 - 2013 Update . 2010 – 2011 Study Plan Fixes Complete. High Voltage in Great Falls and Missoula Areas Mitigated with transformer tap, generator set point, and capacitor setting changes in 2011 - 2012.

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Local Area Study

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  1. Local Area Study Mitigation of High Priority System Problems 2012 - 2013 Update

  2. 2010 – 2011 Study Plan Fixes Complete • High Voltage in Great Falls and Missoula Areas • Mitigated with transformer tap, generator set point, and capacitor setting changes in 2011 - 2012. • Mill Creek 161 kV Bus Outage • Impact of bus outage temporarily mitigated with new South Butte 230/161 kV tie in 2012. Mill Creek 161 kV bus rebuild scheduled for 2014 for final mitigation. • Loss of Rainbow – GF Northeast 100 kV Line • Reconductored the Great Falls 230 kV Switchyard to Montana Refinery 100 kV line to high temperature conductor in 2011 to mitigate overload resulting from outage above.

  3. 2010 – 2011 Study Plan Fixes Complete • Billings Steam Plant 230 kV Air-break Ring Bus • 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 2015 with additional 230 kV breakers at Wicks Lane sub and area 230/100 kV tie. • Missoula 4 161 kV Bus Outage • Added 161 kV breaker to sectionalize bus for bus fault in 2011, in conjunction with 100/69 kV auto bank upgrades.

  4. 2013 Pending Mitigation • Mill Creek 161 kV Bus Outage • Final design and site work for bus rebuild scheduled for 2013. • Breaker ring bus construction to be completed 2014. • Missoula #4 to Hamilton Heights 161 kV lines (N-2) • Convert portions of the 69 kV system from Missoula to Hamilton to 161 kV; Add a 161/69 kV Switchyard at Stevensville. • Substation site selection in progress, construction 2014 – 2015. • Missoula 4 – Stevensville line conversion now scheduled 2016. • Stevi – Hamilton Heights 69 kV conversion 10 – 15 years out. • Columbus Area 50 and 100 kV System (N-1) • New 100 kV line route selection and easement acquisition in progress. Columbus-Rapelje sub upgrade planned for 2014; line construction planned for completion in 2016.

  5. 2013 Pending Mitigation (continued) • Ennis – Lone Mtn 69 kV Line or Ennis 161 kV Bus • Conversion of Jackrabbit to Big Sky 69 kV line to 161 kV in progress. Scheduled for completion in 2014 or 2015. • Billings Area VAR Support • Two 10 MVAR capacitor banks now in service at Laurel Auto. • 20 MVAR capacitor bank planned for Baseline in 2013. • Two 15 – 20 MVA capacitor banks planned for Steam Plant in 2014. • Rainbow 69 kV Bus • Site work planned at Crooked Falls sub in 2013 for new 69 kV bus and associated equipment to be removed from Rainbow Switchyard. 69 kV portion to be complete 2014 – 2015.

  6. Additional Mitigation Plans (2014 and beyond) • Rattlesnake 100 kV Straight Bus • Add a circuit breaker to split/sectionalize bus during a bus fault, scheduled for 2015. • GF – Canyon Ferry – East Helena 100 kV Lines (N-2) • Loss of both lines can overload Holter – Helena Valley Tap Line • Considering breaker(s) at HV tap point for OMS scheme, also reconductoring Holter line later. Second 100 kV feed to Helena Valley sub under consideration also for enhanced reliability and distribution planning needs. • East Gallatin 161 kV Bus Outage • Bus has been resigned to accommodate a breaker-and-a-half scheme and one new 50 kV breaker. Also transfer distribution load to 161 kV. Planned 2017 – 2018, may advance schedule.

  7. Additional Mitigation Plans (continued) • Clyde Park 161/50 Auto • Loss of transformer cause area voltage and thermal problems. Spare on site. Original mitigation: • Add two 9 MVAr capacitor banks in Livingston • Reconductor the Big Timber Auto to Melville 50 kV line • Add second 161/50 kV autobank to Big Timber Auto. • Mitigation plans under review. • Columbus-Rapelje – Alkali Creek 161 kV Line • Loss of this line could create low voltage in the Columbus area. • Will be mitigated with installation of new 230/100 kV tie at Columbus-Rapelje sub (and removal of 161/100 kV tie) in 2014.

  8. Additional Mitigation Plans (continued) • Broadview – Billings Area 230 Double • Loss of both 230 kV lines from Broadview to Steam Plant and Alkali Creek could create low voltage in area, worse after Corette shutdown. • Planned capacitors in area partially mitigate problem. • Newly identified problem; further mitigation under study. • Laurel – Bridger Auto 100 kV A & B Line Outage • Low voltage in area partially mitigated upon completion of new Columbus – Chrome 100 kV facilities. • 6 MVAR capacitor bank planned at Bridger, 2016 estimated.

  9. Additional Mitigation Plans (continued) • Lower Duck Creek – Columbus Rapelje 161 kV Line or Big Timber 161/50 kV Auto Outage • Outage can cause low voltage in Big Timber area 50 kV system. • Addition of 161 kV breakers (and auto bank upgrade) at Big Timber Auto mitigates problem. Scheduled for 2017. • All mitigation plans subject to change or modification as necessary to accommodate changes in load, generation, etc. • QUESTIONS?

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