- Why don’t Idaho Power and/or Rocky Mountain Power place power lines underground?
- Expense: Higher voltage lines, likes those planned for this project, are significantly more expensive and stretch for hundreds of miles; construction and material costs would significantly increase electrical rates for consumers.
- Area of disturbance: A great deal more ground disturbance is required to construct underground rather than overhead facilities. Underground construction requires an approximate 80-foot wide area be cleared of all vegetation and graded for the length of the route. A concrete-encased duct bank system is required for a 500 kilovolt underground line; three trenches of four conduits each in a 2 foot x 2 foot configuration with 20 feet of separation between trenches. The trenches would be centered within the 80-foot wide impact area. An ongoing impact area includes the 14-foot wide access road along the entire length of the route and the area around the vault manholes. Vegetation on the access roads, above the trenches, and around the vault manholes will be cleared annually in order to maintain clear access.
- Life of transmission line: While reliability for underground lines and overhead lines is similar, repairing underground cables is more expensive and much more time consuming. An underground conductor may last only 20 years, whereas an overhead line can last as long as 100 years.
- Are there ways to make the towers less reflective, i.e. less visible?
- Would local companies be able to bid on various aspects of project construction?
By law, it is the responsibility of Idaho Power and Rocky Mountain Power to provide power to customers by the least-cost alternative, and the most affordable industry standard is overhead power lines. It is not uncommon today for smaller distribution lines in a new residential subdivision, for example, to be installed underground at the expense of the developer. The cost to install underground facilities can be many times that of overhead lines. The state public utility commissions have typically directed that these additional costs be borne by those that benefit or cause them to be incurred. Therefore, the cost of placing the lines underground becomes the responsibility of the developer or the homeowner. In the case of the smaller distribution lines, the extra cost may be manageable for those who request it. The cost to install underground facilities is about 10 times that of overhead lines.
Other constraints in using underground lines include:
Galvanized steel lattice towers are the preferred structure type for the project. The tower configuration is open and airy and allows the eye to look through and beyond the structure to 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 appear even more unnatural and often draw more attention than galvanized structures.
Some locations, however, do 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 will have a weathering steel finish, which mimics the visual characteristics of a standard wood pole.
Yes. For vendor and contractor information, click here.
Idaho Power service territory: Included in Idaho Power’s Requests for Bids are specific criteria and qualifications that must be met in order for a bid to be valid. These qualifications include being able to demonstrate experience related to constructing projects of similar scope.
Currently, Idaho Power’s transmission system consists predominantly of 69 kilovolt (kV) to 345 kV facilities. Idaho Power’s planned 500 kV projects, Gateway West and Boardman to Hemingway, are the first 500 kV facilities proposed by the company. Since there have not been projects of this magnitude built in Idaho for over 30 years, most local contractors do not have the experience or equipment necessary to construct 500 kV facilities.
Rocky Mountain Power service territory: Please visit http://www.pacificorp.com/sup.html.