Understanding Transmission - How You Get Your Electricity »

Transmission Q&A

1. What is a transmission grid?

A transmission grid is a network of power stations, transmission lines (or circuits) and substations that are all interconnected to provide a level of redundancy and, therefore, reliable electric service even if an event were to impact the system.

2. What is the difference between alternating current and direct current?

An alternating current flow direction reverses at frequent intervals. Direct current only flows in one direction. Most transmission lines in the U.S. are alternating current.

3. What is the difference between low voltage and high voltage lines?

Transmission lines considered high voltage are classified as 230-kilovolt (kV) and greater (where one kV equals 1,000 volts). High voltage transmission lines are used to move energy farther distances to reduce the energy lost in transmission. Low voltage lines move energy shorter distances.

4. What are electromagnetic fields?

are invisible lines of force that surround any electrical device such as power lines, electric wiring, and electrical equipment. Electric fields are the result of the strength (voltage) of the electric charge. Magnetic fields are the result of the motion (current) of the charge. Wherever electricity is used, EMFs are present.

5. How do electromagnetic fields affect human health?

Since the early 1970s, researchers have investigated the possibilities of health risks due to EMFs. Compiled Scientific   does not show a clear pattern of health hazards pertaining to infrequent high frequency EMF impacts, yet ongoing studies persist to determine the adverse impacts of low-intensity, chronic exposure.

6. What factors are taken into consideration for the construction of a transmission line?

Timeline: On average it can take 10 years or more to build a high-voltage transmission line. This timeline includes planning, scoping, mapping, environmental review, public comment, project approval, permitting, land acquisition, and construction.

Height: In general, for overhead high voltage transmission lines, wires are typically at least 30 feet off the ground. For safety reasons, the higher the voltage, the more distance is required between the conductors and anything that touches the ground. There is no single requirement associated with different voltages. The kind of terrain the line will pass over is also a factor, among other considerations.

Location: Clearance requirements are related to: the height of the wires from the ground; the distance between two towers in a single transmission line or the distance between towers from two or more separate transmission lines built within a single transmission corridor; reliability standards; and the proximity of transmission lines to roads and highways. These requirements are mandated by federal, state, and sometimes local governments and the specific requirements are a function of exactly where the line and towers will be located.

Co-Location: Co-location is the term for adding a new transmission line to a pre-existing transmission infrastructure or adding a new transmission line adjacent to an existing transmission line. Clearance requirements and reliability standards are to be met when co-location is being considered. Some key considerations in evaluating whether co-location is a viable option include whether an existing tower can support the added weight of an additional set of wires and how reliability will be hampered by two lines relying on the same towers. Co-location can also help to minimize land use and environmental impact.