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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.

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 (

South Dakota

  • Voltage levels ranging from 34.5 kilovolts to 345 kilovolts
  • Extends throughout the middle of eastern South Dakota along the James River
  • Interconnections include Western Area Power Administration (WAPA), Montana-Dakota Utilities Co., Otter Tail Power Company and Xcel Energy.
  • Emergency interconnections with East River Electric Cooperative, Inc. and West Central Electric Cooperative

On October 1, 2015 NorthWestern Energy joined Southwest Power Pool, Inc. (SPP), and transferred functional control of eligible 69-kV and 115-kV South Daktota 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).

Transmission service for deregulated retail access is still currently being provided under the NorthWestern-South Dakota FERC:  Open Access Transmission Tariff (OATT)

For more information about our Electric Transmission Services, you may contact us via email or call (605) 995-4416.

FERC Order 890 requires transmission providers to post on Web site all of their business rules, practices and standards that relate to transmission services provided under the pro forma OATT. Below are the links to NorthWestern Energy's documents.

The following South Dakota local area planning documents are posted pursuant to the South Dakota Attachment K.

The following document is posted for information purposes at this time and is South Dakota’s FERC Order 1000 response for public policy posting requirements.

NorthWestern has requested an effective date of October 1, 2013 for implementation of FERC Order 1000. Until then the following information is informational.

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