Transmission Q&A
1. How does the transmission grid work?
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 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. How long does it take to build a transmission line, from the planning stages through the completion of building?
On average it takes 10-15 years to build a high-voltage transmission line. This timeline includes planning, scoping, mapping, environmental review, public comment, project approval, permitting, land acquisition and construction.
5. What determines the height of transmission lines?
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. In general, for overhead high voltage transmission lines, the wires are typically at least 30 feet off the ground.
6. Where are these lines and towers allowed to be placed?
Clearance requirements are related to a few issues, including: the height of the wires from the ground; the distance that must be 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.
7. What are the disadvantages of underground transmission lines?
The higher the energy transmitted, the more heat is generated. With overhead transmission lines, the air surrounding the lines acts as an insulator and absorbs this waste heat. In underground transmission lines other mediums must be used to dissipate this heat, which to-date has restricted the undergrounding of transmission lines to voltages less than 500-kV except for very short distances.
Another consideration of underground lines is the ground disturbance caused by the tunnels through which the transmission line runs. Instead of impacting the ground only at tower footings, underground transmission construction requires extensive excavation and can disrupt habitats or water resources. Access to the underground transmission line, which is needed for maintenance and repairs, requires construction of "vaults", typically 20' x 30' structures (roughly the size of an average living room) that must be buried in the ground every 750-1,000 feet where the conductors are spliced together. The environmental and land disruption impacts of undergrounding transmission lines can greatly exceed that of above ground transmission, and are factors that are weighed in the planning process.
8. What is co-location?
Co-location is adding a new transmission line to a pre-existing transmission infrastructure. Clearance requirements and reliability standards both come into play 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.
9. What are electromagnetic fields?
Electromagnetic fields (EMFs) 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.
10. How do electromagnetic fields affect human health?
Since the early 1970s, research has been performed to determine if EMFs pose a health risk. This body of scientific evidence does not show a clear pattern of health hazards.
11. Why is additional transmission needed in Northern California?
The COTP was the last transmission line built to bring additional energy into California, and it is the youngest of the three major transmission lines that bring power from the Pacific Northwest to Northern California. The other two lines were completed in the 1960s, making them nearly a half-century old. According to the California Energy Commission (CEC), California's most critical energy infrastructure issue is its electric transmission system, which is steadily declining in system reliability and increasing in operational costs. In 2008, congestion and related reliability services cost Californians approximately $232 million, up from $221 million in 2007, according to the Cal-ISO Market Issues and Performance 2008 Annual Report. The CEC has warned that California's energy infrastructure maybe unable to meet the state's future energy needs, which include providing heat, air conditioning and light to an estimated 60 million people by 2025.
12. How will additional transmission help meet California's green energy goals?
According to the CPUC, currently about 15 percent of California's energy is from renewable energy resources. The requirement of California's Renewables Portfolio Standard (RPS) is to have at least 33 percent come from these sources by 2020. Not only will new transmission relieve the burden on the existing lines and help ensure a continued supply of reliable and affordable energy, it will also tap into green energy resources (e.g., wind, solar, geothermal and small hydroelectric) that currently have no way of reaching homes and businesses.
In fact, the California Public Utilities Commission (CPUC) recently issued a report that concluded that up to 11 new major transmission lines will be required for utilities to satisfy the state's RPS goals.
13. What will it cost to meet California's transmission needs? How long will it take?
The 11 new transmission lines the CPUC estimates will be needed - just to meet California's RPS goals - are projected to cost $16 billion. Three of these lines are currently under way, but the California Public Utilities Commission predicts that even if implementation on all the other lines were to start today, it would take another 14 years to achieve the 33 percent RPS requirement.
14. What steps are being taken to address California's transmission needs?
The Renewable Energy Transmission Initiative (RETI) developed a set of recommended transmission projects that could accommodate California's renewable energy goals and facilitate the process of developing, generating and transmitting energy from renewable sources.
In addition, the California Transmission Planning Group (CTPG) was formed as a result of discussions facilitated by FERC to address California's transmission needs in a coordinated manner that would respect various business models. The CTPG includes transmission owners with an obligation to serve and transmission operators, and these parties have the technical capability to perform detailed transmission planning.
In February, 2011, CTPG released a California statewide transmission plan to meet the State's RPS requirement of 33 percent by 2020. This transmission plan will seek to leverage a diverse portfolio of renewable energy generation technologies (wind, geothermal, hydro, biomass and solar) available to supply projected electricity demand in California from now to beyond 2020. In this effort CTPG is utilizing the RETI conceptual plan as a starting point.
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