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Local Area Study

Local Area Study. Mitigation Plan Update and Uncertainty Scenarios 2012 - 2013. Mitigation Plans Updates. East Helena bus fault or transformer outage Ranked # 7 - Outages result in complete loss of the Helena 69 kV system

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Local Area Study

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  1. Local Area Study Mitigation Plan Update and Uncertainty Scenarios 2012 - 2013

  2. Mitigation Plans Updates • East Helena bus fault or transformer outage • Ranked # 7 - Outages result in complete loss of the Helena 69 kV system • Construct 100 kV loop to radial fed Helena area 100 kV distribution substation • Tie proposed distribution substation needed for continued growth in the Helena area to new 100 kV facilities • Construct and tie new 100 MVA 100/69 kV auto substation to new 100 kV facilities • Add breakers to East Helena 69 kV bus to complete breaker-and-a-half scheme

  3. Mitigation Plans Updates • Broadview to Billings Area 230 kV double contingency • Ranked # 8 - Outage results in low to very low voltage in the Billings Area • Problem worsens after loss of Corette and continued Billings area growth • Build a new 230 kV line from Broadview into Billings • Assumes slightly diverse route from existing Broadview to Billings 230 kV lines • Clyde Park bus fault or transformer outage • Ranked # 13 - Outages result in loss of Livingston and Big Timber Loads • Upgrade Big Timber Auto to a 50 MVA transformer • Reconductor weak 50 kV line near Big Timber • Add capacitors to Big Timber and Livingston area distribution substations

  4. Uncertainty Scenarios Scenarios Considered: • Extreme Winter • Low Thermal, Heavy Import • High Wind System Wide • High Generation North of Great Falls (NOGF) • Similar to stakeholder suggestion Study Assumptions: • N-0 and N-1 conditions considered • All existing Special Protection Schemes considered

  5. Extreme Winter Scenario Details • 2017 Extreme Winter load profile (1:50 forecast) • Hydro plants significantly reduced • Rivers/reservoirs partially frozen • Thermal plants dispatched at max • Corette assumed to be mothballed • Wind dispatched at 5% Scenario Findings • 230 kV and 161 kV systems more heavily relied on to supply the underlying 100 kV systems • Loss of Butte area 161/100 kV tie overloads remaining 161/100 kV tie • 100 kV system in Judith Gap area overloads from loss of major 230 kV line in Great Falls area

  6. Low Thermal, Heavy Import Scenario Details • 2017 Heavy Summer load profile • All major thermal plants are offline • Wind dispatched at 5% • Path 8 heavily importing Scenario Findings • Kalispell 115 kV tie line overloads (within emergency limits) for the loss of Rattlesnake 230/161 kV auto transformer • Loss of Butte area 161/100 kV tie overloads remaining 161/100 kV tie • Steamplant bus outage causes additional overloads on Billings area 100 kV ties to the higher voltage BES

  7. High Wind System Wide Scenario Details • 2017 Heavy Summer and Light Autumn load profiles • Existing wind projects dispatched at capacity • All other generation dispatched same as original case • MATL has little to no flow at Great Falls Scenario Findings • No new thermal issues • Minor high voltage under outage conditions identified in Two Dot area

  8. High Generation NOGF Scenario Details • 2017 Light Spring load profile • Great Falls and NOGF area hydro generation at max • Other Montana hydro dispatched same as original case • Great Falls and NOGF area wind generation at max • Remaining wind generation dispatched at moderate levels • MATL importing at Great Falls near 300 MW • Path 8, 18, 80 transfers similar to original case

  9. High Generation NOGF Scenario Findings • Butte area 100 kV line heavily loaded under N-0 conditions • Loss of Great Falls – Ovando 230 kV line overloads 100 kV lines in Helena area • Loss of Great Falls – Judith Gap – Broadview 230 kV line overloads 100 kV lines in Harlowton, Judith Gap, and Broadview areas

  10. Conclusions • System still robust in most areas, few new potential problems found. • Benefits of widely dispersed generation are demonstrated. • Potential weaknesses in the 100 kV system were identified. • Line or transformer upgrades and/or new facilities could be required to mitigate problems observed. • This analysis is “Informational” and not the primary driver for mitigation. • Because of the uncertain nature of these scenarios, formal mitigation plans have not been developed. • In some cases, new generation or TSR requests would drive mitigation for problems observed.

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