- How much right of way width does a 500 kilovolt (kV) transmission line require?
- Why doesn't Idaho Power place power lines underground?
Costs: Estimates vary widely, but literature indicates costs could be as much as 10 to 20 times the cost of overhead transmission lines. It is the responsibility of Idaho Power to provide power to customers using the least-cost alternative. The most affordable industry standard is to use overhead power lines.
- Limited experience: There have been very few projects that have involved 500 kV underground transmission and construction within the United States or worldwide.
- Less capacity: Underground cables carry far less capacity than overhead lines in similar sized cables, therefore, much larger cables are required to achieve the same capacity.
- Operations and maintenance: While underground lines would be less susceptible to weather related outages (e.g., wind, ice, fire and trees). A cable failure would be more difficult and take longer to repair. When repairs are needed, greater time constraints are required to find, excavate and fix the problems. When a failure of underground equipment does occur, the repair times on an underground cable can be expected to take more than two weeks per segment of cable (even if a spare duct bank and material are readily available), whereas repairs on an overhead segment can be completed much faster.
- More equipment: Typically, more aboveground substations are required for underground lines. In addition, underground splice vaults (large concrete encased structures) are required approximately every 1,200 to 1,600 feet.
- Disturbance and impact: Underground transmission lines require large excavations through all habitat types. An approximate 80-foot-wide area is needed to be cleared and graded for the length of the route for underground lines. The right of way needs to remain free of woody vegetation to prevent interference to the underground lines from tree roots. Access roads also need to be maintained for underground lines for maintenance and repair.
- Less reliable: Underground systems tend to be less reliable than overhead installations due to a variety of factors (e.g., conductor heat buildup, underground water and bacteria). An underground conductor may last only 20 years, whereas an overhead line can last as long as 100 years.
- Visual resources: Underground lines would remove most of the concerns of visual impacts associated with a traditional overhead transmission line system but the right of way could be more visually apparent due to vegetation management.
- What would the towers look like?
- Are there ways to make the towers less reflective, i.e., less visible?
- Will the transmission towers be the same height as wind turbine towers?
- What would the average cost per mile be to build the line?
- Could existing transmission lines be modified to carry more power?
- Would Idaho and Oregon companies be able to bid on various aspects of project construction?
- When would construction begin?
- Where can I get information on construction contracting and bidding opportunities for the project?
- What kind of access for maintenance would be required once the lines and substations were built?
The right of way for the B2H Project would be approximately 250 feet wide.
While technologies are emerging for underground transmission lines, there are currently disadvantages to using them. Reasons for not using underground transmission lines for the B2H Project include:
A variety of transmission line structure designs may be used for the project. The structures may be a combination of single circuit towers, h-frame and steel lattice and tubular steel towers.
Visit Idaho Power’s Design and Construction pages to view the proposed transmission line structure.
Galvanized steel lattice towers is one of the proposed structure types for the B2H Project. The tower configuration is open and airy and allows the eye to look through and beyond the structure to view objects in the background. Typically, the dull finish of the galvanized steel is muted against a variety of backdrops, whether against a hillside, forested land or even the sky. Painted structures are typically not used as they appear more unnatural and are more visible than galvanized structures.
Some locations, however, may require the use of other structure types to minimize visual and resource impacts. H-Frame structures, which consist of two tubular steel poles and a cross arm, may be used in some areas where shorter spans can be utilized or are necessary. H-Frame structures would have a weathering steel finish, which mimics the visual characteristics of a standard wood pole.
No, the transmission towers are about half the height by comparison. They will range between 110 and 190 feet depending on the structure type needed to cross the terrain. Typically tubular towers for wind turbines, including the height of the blades, range from 300 feet to more than 400 feet. To see images of the transmission line towers planned for B2H, visit the Design and Construction page.
The preliminary cost estimates for 500 kV transmission lines range from approximately $1.25 million to $2.0 million per mile of construction for a single circuit transmission line. These costs are estimates based on past projects and industry experience. However, many intangible variables can vary the cost significantly, including rights-of-way costs, necessary substation and line equipment, accessibility and mitigation measures.
Yes, some lines could be modified to carry more power. However, the lines that deliver power into Idaho from the Northwest are generally not capable of being upgraded. This is because the towers that support these existing lines are not capable of carrying larger wire and would have to be replaced. If these towers were replaced to carry a 500 kV line for the B2H Project, all of the lines that deliver power from the Northwest into Idaho would have to be upgraded to meet redundancy requirements. This means that multiple lines must available – and physically separated by a certain distance – to carry all the electric supply in the event one of the lines fails (equipment damage, storm, etc.) The existing lines are rated at 230 kV and would not have the capacity that can be provided by a 500 kV line.
Due to the magnitude of the job, Idaho Power plans to contract with construction companies to build the proposed line. Idaho Power project leaders would oversee and manage all design and construction activities.
Construction of the proposed transmission line would begin after Idaho Power receives permits from the federal agencies and an Energy Facility Site Certificate from ODOE-EFSC.
The project is currently in the permitting phase with BLM/USFS/ and ODOE. If you are interested, please use the following link to add your business to Idaho Power’s potential contractor list.
Idaho Power inspectors would perform inspections on foot, in a four-wheel drive vehicle or from the air using a helicopter. Predetermined access routes would be used to access the facilities for inspections.
Idaho Power inspects transmission lines twice a year and substations are inspected monthly. Maintenance would require access to any portion of the line with specialized equipment to allow safe and efficient repair of the facility. Emergency maintenance would require access on an as-needed basis to promptly repair or replace any damaged or missing equipment.