The 1,609km Gateway West transmission line will improve current transmission mainly in the states Idaho and Wyoming in the US. Image courtesy of Gateway West Transmission Line project.
The project is part of the Energy Gateway transmission expansion project.

The 1,609km-long Gateway West transmission line is being built across the states of Wyoming and Idaho in the US.

The project is being undertaken by Idaho Power and PacifiCorp’s subsidiary, Rocky Mountain Power. The two companies jointly proposed the project in May 2007 as project proponents.

The transmission line is a part of PacifiCorp’s Energy Gateway transmission expansion project. It was approved considering the need to improve reliability and deliver electricity from existing and new generating resources such as coal, solar, hydroelectric, geothermal, natural gas, and wind across the western part of the US.

Construction of the Aeolus to Bridger/Anticline sub-segment of the project started in April 2019 and it is expected to come be commissioned by December 2020. The entire project is expected to be completed by 2024.

Energy Gateway transmission expansion project

PacifiCorp’s Energy Gateway transmission expansion project aims to develop more than 3,000km of transmission network across the western part of the US. The project is divided into four parts named Gateway Central, Gateway West, Gateway South, and West of Hemingway.

Gateway Central includes three segments located in Utah and Idaho. Two sub-segments of the segment have been completed and are in service. The Gateway South segment includes two segments in Wyoming and Utah, one of which has been completed and is in service. The West of Hemingway segment will be built in Washington and Oregon.

Construction of the Gateway West sub-segment was announced in April 2017, while construction of the Gateway South segment was announced in October 2019.

The project will support PacifiCorp’s $3.1bn Energy Vision 2000 aimed at adding 1.15GW of new wind resources as well as upgrading existing wind resources.

Gateway West transmission line route details

The Gateway West transmission line includes two segments – Segment D and Segment E. Segment D is further subdivided into D.1, D.2 and D.3.

The D.1 sub-segment will be a 121km-long, 230kV single-circuit line extending from Windstar substation in Wyoming to the planned Aeolus substation near Medicine Bow in Wyoming.

The D.2 sub-segment will be a 225km-long, 500kV single-circuit line connecting the Aeolus substation to a new substation near the existing Bridger/Anticline substation in western Wyoming. The D.3 sub-segment will be a 322km-long, 500kV single-circuit line connecting the Bridger/Anticline substation to the Populus substation near the city of Downey in Idaho.

Segment E includes two 808km-long, 500kV single-circuit transmission lines originating from the Populus substation to the Hemingway substation near Melba, Idaho.

The Populus to Hemingway segment will also comprise of five expanded/new substations and enable connection to power generated from conventional as well as new sources such as wind.

Gateway West transmission line infrastructure details

The project will use three type of structures with a combination of single and double circuit towers, and steel lattice and tubular steel towers made of galvanised steel.

The 230kV single circuit lines will use H-frame steel towers with a height of 60ft-90ft. The towers will have a ground clearance of 28ft, an average span of 800ft, and right of way of 125ft.

The 500kV single circuit lines will feature steel lattice towers with a height 145ft-180ft and ground clearance of 35ft. The average span of the towers will be 1,200ft-1,300ft, and right of way will be 250ft.

Contractors involved

Quanta Services was awarded the engineering, procurement, and construction (EPC) contract for the Aeolus-Jim Bridger sub-segment of the project.

WLC Engineering and Surveying was contracted to perform land surveying for the expansion of Windsor substation and tie-ins of 230kv transmission lines.

AECOM and Tetra Tech jointly prepared the environmental impact assessment of the project for the Bureau of Land Management (BLM).