About the project
Idaho Power is planning the Mayfield Substation and Transmission Line Project to strengthen our regional grid and support reliable, affordable energy for customers across southern Idaho. This new substation is envisioned as a critical hub in our transmission network, helping us deliver power more efficiently and reliably as our communities grow.
Substations are placed where they’re needed most, where electrical demand is high and where there is good access to major transmission lines. The proposed Mayfield Substation would be built near an existing 500-kilovolt (kV) transmission line, on land Idaho Power purchased in the 1980s to support future energy needs. The location also aligns with a future segment of the Gateway West transmission project and is near several 230-kV lines already in operation.
Connecting these high-voltage lines at a central point like Mayfield with new 230-kV lines would improve the overall flow of power on the grid, ease pressure on existing lines, and provide more flexibility to move electricity where and when it’s needed. This means better service and fewer interruptions for customers from the Treasure Valley to the Magic Valley and beyond.
The Mayfield Substation is part of our long-term plan to serve growing energy needs while keeping power reliable and affordable for the communities we serve.
Frequently Asked Questions
What will the substation and transmission lines look and sound like?
The substation will look similar to other Idaho Power substations with fencing around the entire site. Transformers can produce a slight hum when standing within the site. The new 230-kV transmission lines are single-poles with three lines of wire running between them. Depending on the weather, a faint sound may be heard from the transmission lines connecting the station to the grid.
How will the substation be kept safe and secure?
Safety is a top priority for Idaho Power. The planned Mayfield Substation will be designed to meet strict industry standards for both public and worker safety, as well as wildfire prevention. The location gives us enough space to follow best practices for substation layout and fire mitigation.
The site will be fully enclosed with a high-security fence, including a stamped concrete wall along the frontage road and mesh steel fencing around the rest of the perimeter. It will also feature deterrent and detection devices to prevent unauthorized access. Only trained Idaho Power personnel will be allowed on site, and we work closely with local emergency responders to ensure they’re familiar with the facility.
Substations like this operate safely in communities across Idaho every day, helping ensure reliable energy while maintaining a strong focus on safety and security.
Why is this location being considered for the Mayfield Substation and transmission lines?
This location offers a unique opportunity to strengthen the power grid efficiently and cost-effectively. Idaho Power purchased the land in the early 1980s when the first 500-kilovolt (kV) transmission line was built across southern Idaho, specifically with future infrastructure in mind.
The site is ideally situated near both this existing 500-kV line and several 230-kV transmission lines already in operation. It’s also close to the new Pleasant Valley Solar Substation. Connecting these facilities at a single point will help improve the flow of electricity across the region, reduce strain on the system, and support the reliable, affordable service our customers count on.
Is the Mayfield Substation and transmission lines just being built to serve large businesses or new developments in the Treasure Valley?
No. The Mayfield Substation is needed for Idaho Power to meet growing energy demand in the Treasure and Magic Valleys. The Mayfield Substation property was purchased over 40 years ago in anticipation of this substation hub being needed to serve long-term growth. Idaho Power is now at the point where the project is necessary to serve our growing customer base.