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NWE Contact Bar, in Montana dial 1-888-467-2669, in South Dakota or Nebraska dial 1-800-245-6977
small brandlElectric Transmission

Electric Distribution 


  • 363,800 customers
  • 187 communities
  • Revenue by category 
    • 40% residential,
    • 50% commercial and industrial
    • 10% other
  • 17,750 miles of overhead and underground distribution lines
  • Service territory covers approximately
    73 percent of Montana's land area
  • 2016 peak demand 1,808 MW
  • Average daily load 1,239 MW

South Dakota  

  • 63,200 customers
  • 110 communities
  • Revenue by category
    • 39% residential
    • 59% commercial and industrial
    • 2% other 
  • 3,550 miles of overhead and underground distribution lines
  • 2015 peak demand 330 MW
  • Average daily load 187 MW

Electric Transmission 


  • 6,700 miles of transmission lines and associated terminal facilities
  • Voltage levels ranging from 50 kilovolts to 500 kilovolts
  • 288 circuit segments
  • Approximately 104,000 transmission poles
  • Extends throughout the western two-thirds of Montana from Colstrip in the east to Thompson Falls in the west
  • Jointly owns a 500 kilovolt transmission system that transfers electricity generated from the 2,180 megawatt Colstrip generation facility to markets within the state and west of Montana
  • Interconnections to five major nonaffiliated transmission systems located in the Western Electricity Coordinating Council (WECC) area
  • One interconnection to a system that connects with the Mid-Continent Area Power Pool (MAPP) region
  • Directly interconnected with Avista Corporation, Idaho Power Company, PacifiCorp, the Bonneville Power Administration, Montana Alberta Tie Ltd., and WAPA.

Transmission reservations for service over the Montana system occur on NorthWestern Energy's Open Access Same-Time Information System (OASIS) – Transmission service for both wholesale and deregulated retail access are provided under the FERC electric Open Access Transmission Tariff (OATT) located on the NorthWestern Energy OASIS site under the "Tariffs / FERC Filings" folder located on the left hand side of the OASIS page. Formula Rate postings for transmission service under the Montana OATT are also available in the “Tariffs / FERC Filings” folder on OASIS.

For more information about our Electric Transmission Services, you may contact us via email or call (406) 497-4500.

FERC Order 890 requires transmission providers to post on OASIS all of their business rules, practices, and standards that relate to transmission services provided under the pro forma OATT.  Below is a link to NorthWestern Energy's OASIS (

Montana Electric Transmission Planning Study

NorthWestern Energy studied several scenarios to determine the critical role of the 500 kV transmission line from Colstrip in the reliable operation of the Montana transmission system used to deliver energy to industrial, retail and residential customers.  The Colstrip Transmission System is especially important as additional Montana generation is slated to be shuttered.

That 250 mile line, which runs west from Colstrip, interconnects with the Bonneville Power Administration’s Eastern Intertie at Townsend, providing access to markets and energy supply in the West at the most critical times. The Colstrip Transmission System is jointly owned by the multiple owners of the Colstrip Power Plant.  

NorthWestern Energy is a 10 percent owner in Colstrip generation and is currently a 31 percent owner in the transmission line. 

The study confirms that if the transmission line is decommissioned, NorthWestern Energy will have to make significant investments to handle peak customer energy needs,  and to import enough energy from the West to provide reliable service to Montana customers.  These investments would likely far exceed the depreciated costs of the entire Colstrip Transmission System – including the portion of the system owned by the other Colstrip participants. 

Additional ownership of the Colstrip Power Plant provides NorthWestern Energy the opportunity to purchase additional ownership of the Colstrip Transmission System and to influence that asset’s future, preserving its functionality so that it can continue to serve Montana customers’ energy demands


South Dakota

On October 1, 2015 NorthWestern Energy joined Southwest Power Pool, Inc. (SPP), and transferred functional control of eligible 69-kV and 115-kV South Dakota transmission facilities. SPP is a Regional Transmission Organization (RTO) that serves as a single Balancing Authority (BA) for interconnected electric utilities in 14 states. Our South Dakota qualifying facilities are part of the Upper Missouri Zone (UMZ or Zone 19) within SPP, and transmission service for wholesale is being provided under SPP's Open Access Transmission Tariff (OATT). Formula Rate postings for transmission service under the SPP OATT are available on the SPP Member Related Postings page.

For more information, you may contact us via email or call (605) 995-4416.

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