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Southeastern Idaho Transmission Project
Transmission Line
Miles: 44.0
Percent Operating: 100.0% (44.0 of 44.0 mi.)
Segments Operating: 4 of 4

Description: The project requires a multi-stage upgrade to the electrical system from Goshen Substation, near Firth, Idaho, to Rexburg Substation, in Rexburg, Idaho.

From Goshen Substation through Ammon Substation and to Sugarmill Substation, an existing 69-kV transmission line will be rebuilt for 161 kV operation. Goshen Substation will also be upgraded with an additional 345-kV/161-kV transformer and an expanded 161-kV breaker yard. Ammon Substation will be converted to receive 161 kV transmission, and Sugarmill Substation will be upgraded with a 161 kV breaker yard expansion.

From Sugarmill Substation to Rigby Substation a new 161 kV transmission line will be constructed. After generally exiting north out of Idaho Falls, the new transmission line will follow Ririe Outlet Canal and then go north along Lewisville Highway to 400N in Rigby where the existing 69-kV line from Roberts will be rebuilt to 161 kV. Rigby Substation will be upgraded with a 161-kV breaker yard.

From Rigby Substation to Rexburg Substation, an existing 69-kV line is currently being rebuilt to 161 kV. Also, Rexburg Substation will be upgraded to receive 161-kV transmission.

Also, for a certain portion of this project, Rocky Mountain Power is working with Idaho Falls Power to jointly construct and operate a portion of the transmission line. This coordination eliminates the need for two separate lines (one for each company) and reduces costs.

Analyst Notes:

Key Dates:

Companies Involved:
Company NameCompany Role
Idaho Power •••••••••••••
Rocky Mountain Power •••••••••••••
Rocky Mountain Power •••••••••••••
PacifiCorp •••••••••••••
Goshen-Ammon161 kV14.0 miOperating
Ammon-Sugarmill161 kV5.0 miOperating
Sugarmill-Rigby161 kV13.0 miOperating
Rigby-Rexburg161 kV12.0 miOperating