Project Need

Increases in usage and demand for electricity have severely strained Idaho Power’s existing electrical transmission facilities in the Treasure Valley.

In order to continue to provide reliable electric service to its customers, and to meet existing and future electrical transmission capacity needs, Idaho Power plans to replace an existing 138,000-volt (138-kV) transmission line between its Danskin and Hubbard substations with a new 230,000-volt (230-kV) transmission line.

Danskin substation is located just north of Mountain Home while the new Hubbard Substation will be located southwest of Boise. The line route crosses Interstate 84 and passes through federal, state, and privately owned lands. This project includes removal of the existing 138-kV transmission line and then construction of a new 230-kV line in within the same corridor. The required in-service date for the new 230-kV line is September 2008.

Transmission Line Details

After removal of the existing 138-kV transmission line between Danskin and Hubbard substations is complete, the new 230-kV transmission line will be constructed in the same route.

The new 230-kV line will use a two-pole structure with horizontal cross-arms, similar to the 138-kV line currently there. Poles will be steel and slightly larger to accommodate the increase in voltage rating.

While the existing line route will be utilized, individual structure locations within the line route will change to optimize the line design.

Details of the new 230-kV Danskin-Hubbard transmission line are as follows:

• Danskin-Hubbard line miles: 40
• Distance on U.S.-owned lands: 14 miles
• Distance on state-owned lands: 5 miles
• Distance on private lands: 21 miles
• Structure type: Two tubular steel poles with horizontal steel cross-arm
• Structure materials: Weathering steel
• Foundations: Direct embedded poles
• Structure heights: 70 to 80 feet average
• Structure spacing: 600 to 1,000 feet average