An example of how an Idaho Power substation appears in an urban setting.

Idaho Power Company is committed to providing its customers with reliable electric service. In keeping with this commitment, Idaho Power added the Happy Valley Substation and associated 138,000-volt (138-kV) sub-transmission line. These facilities allow Idaho Power to continue providing reliable electric service and to meet both existing and future electrical capacity needs for the southeast Nampa area.

Project Need
According to U.S. Census figures, Canyon County was one of the fastest growing areas in the nation with a population jump of more than 15 percent between 2000 and 2003. Idaho Power connected an average of nearly 3,000 new electrical customers per year in Canyon County during that same period. This growth has substantially increased Idaho Power’s electrical load and is straining existing electric facilities.

Project Details
Happy Valley Substation is located on the east side of Happy Valley Road, north of the Union Pacific Railroad intersection. Click for a printable map (PDF, 448KB).

The substation transforms electricity from 138kV to 12.5kV, and will initially be designed to serve three 12.5-kV distribution circuits that bring electricity from the substation to homes and businesses in the area. As the southeast Nampa area continues to grow, up to five additional 12.5-kV distribution circuits could be installed.

The substation will ultimately serve as a regional transmission resource transferring energy between other transmission substations in the Treasure Valley. The substation will likely serve two 138-kV sub-transmission lines and two 230-kV transmission lines over the next 10 to 15 years.

Sub-Transmission Details and Route Selection Process
The 138-kV sub-transmission line begins at the existing Chestnut Substation located on South Chestnut Street (near the intersection of East Amity Avenue and South Powerline Road) and terminates at the Happy Valley Substation. In general, the poles are designed with the 138-kV sub-transmission circuit in the top position and two 12.5-kV distribution circuits in lower positions. Road right of way or private easements were used for the line corridor.

• Structure type: Tubular steel poles


• Structure color: Hazelton gray


• Structure heights: 75 to 85 feet


• Structure spacing: 300 feet average

Idaho Power has incorporated public comments and regulatory constraints in selecting the 138kV sub-transmission line route. See Project Schedule for more details.