Mountain States Transmission Intertie

Mountain States Transmission Intertie is a 430-mile line, 500-kV transmission line that will cost $1 billion. The project, which is proposed by NorthWestern Energy, will begin at the new Townsend Substation, which will be constructed about five miles south of Townsend, Mont. The line is being designed to proceed south into southeastern Idaho connecting to Idaho Power Co.’s existing Midpoint Substation, 10 miles north of Jerome, Idaho. The project will address the need for new electric transmission service from generating sources to customers and to help bolster the western power grid. On January 11, 2012, NorthWestern and BPA signed a Memorandum of Understanding (MOU) agreeing to explore the potential of a MSTI Project that would accommodate both parties’ needs. The MOU stipulates that by July 31, 2012, the parties seek to complete economic and engineering viability studies and a capacity and cost allocation methodology that considers other partners in the line and treatment for unsubscribed capacity and cost. The outcome of these studies will provide information necessary for BPA to determine whether or not to consider future agreements for participation in the MSTI project. In October 2012, NorthWestern Energy announced that the Bonneville Power Administration notified them that it won’t use the MSTI to serve BPA’s southern Idaho loads. In July, the company said if an agreement with the BPA was unlikely, it may have to abandon the project. NorthWestern will continue to monitor market conditions and evaluate options related to the MSTI project. According to NorthWest Energy’s website the project has officially been put on hold due to market uncertainty and permitting issues. The original in service date was 2018.

Project Sponsor Line Miles Voltage (kV) From State To State Year in Service
NorthWestern Energy 430 500 MT ID 2017
Estimated Costs ($M) Voltage Type Project Status Project Group Origin Point Destination Point
1000 Suspended Townsend Midpoint Substation near Jerome
Interstate Build Start NERC ISO/RTO Country Project Partners
2015 WECC US