Frequently Asked Questions (FAQs)

345-kV single-pole structures are steel poles and vary in height from 120 to 170 feet, and spans (or distance) between structures range from 800 to 1,200 feet. H-frame structures are two wood or steel poles with cross bracing and conductor supports. They can be embedded in the ground without a foundation and vary in height from 75 to 150 feet; spans between structures range from 600 to 900 feet.

The heights of the structures for 345-kV segments are generally 120 to 170 feet and 100 to 150 feet for 230-kV segments, depending on terrain, span length, conductor tension and the type of structure. Structures requiring greater height for clearance reasons may be used in certain instances. 230-kV conductors are generally 28 feet above the ground, and 345-kV conductors are generally 32 feet above the ground at the lowest point during maximum operation conditions and may have higher ground clearance in areas where snow accumulation or agricultural activities under the line may be a concern. Once engineers have designed the line, specification details will be provided for each property.

The utilities must approach all projects from a prudent business position and as such are proposing overhead lines because of reliability and cost. Underground transmission lines generally cost up to 10 times as much as overhead lines. The technology to build lines underground for long distances is also extremely difficult to manage. With overhead lines, air cools the lines and keeps them at a safe operating temperature. Underground lines require cooling mechanisms, which increases cost and decreases reliability. Locating and repairing underground line failures also takes longer, leading to longer outages. The reactive losses of underground lines are substantially higher than overhead lines, and installation requires lengthy, disruptive construction techniques. Design concerns such as capacity and heat dissipation are frequent limitations. Underground systems are justified primarily in heavily populated downtown urban centers, where right-of-way is severely limited for overhead lines.

However, if the landowner/developer/jurisdiction pays for the differential in cost, and, if the feasibility analysis shows that it can be safely constructed and operated underground, PSCo will consider the request to build the line underground. For further information please see the Overhead vs. Underground fact sheet.

Every effort is made to ensure safety in construction, operation and maintenance of transmission lines. Lines and line infrastructure are designed to withstand extreme weather conditions. Protective devices at line terminals stop the electricity flow under any abnormal operating circumstances. Utility practices meet or exceed standards set by national electric safety codes as well as those adopted by local governments.

All construction projects have a certain degree of construction noise; however, the proposed projects will have adequate setbacks to reduce noise impact to residential and commercial neighbors. Some noise will be generated during the construction period from construction machinery and employee vehicle traffic. Construction vehicles and equipment will be required to be maintained in proper operating condition and equipped with manufacturer’s standard noise devices or between (e.g., mufflers, engine enclosures). High voltage transmission lines do have a tendency to emit noise when they are wet. However, the proposed transmission lines will be designed to operate within the noise parameters deemed reasonable by the CPUC, which is the legal authority in the state to make such a determination.

Several factors produce audible noise on high voltage transmission lines. Corona is a small electrical discharge, not unlike the static electrical charge that a person may experience when touching a metal object while walking on carpet. Corona is what creates the hissing, crackling or random popping sound. It increases substantially in wet weather, when water droplets form on a transmission line. All high voltage transmission lines experience corona during wet weather. In fair weather conditions, corona and its corresponding audible noise are usually at low levels. The higher the voltage on the transmission line, the greater the corona activity on the line.

Corona on transmission line conductors can generate noise at the frequencies at which radio and television signals are transmitted. This noise can interfere with receiving of these signals and is called “radio interference” and “television interference,” depending on the frequency.

AM radio reception (535 to 1605 KHz) is most often affected with what is commonly referred to as static. FM radio reception is rarely affected. Corona can affect the reception of the video (picture) portion of a television screen.

Corona effects from the proposed projects are expected to be low enough so that no objectionable audible noise or radio or television interference will result outside the right-of-way. If any problems do occur, transmission line maintenance activities are intended to locate and correct these problems. The line will use corona-free hardware to minimize noise.