Transmission 101

In almost all cases, the electricity that powers the computer or mobile device you are using right now traveled a significant distance across the high-voltage transmission system, and through the lower voltage power lines in your neighborhood, to reach the outlet in your home where you plug in your device or charger.

Miles and miles of transmission lines

Transmission lines are essential for moving electricity from where it is produced to where it is consumed. The United States has more than 200,000 miles of high-voltage transmission lines, which serve much like the interstate highway in facilitating electricity commerce and providing consumers with lower-cost electricity.

The transmission network then connects to the smaller distribution power lines, the equivalent of smaller local roads, to bring that electricity into your home.

Transmission network divided into three areas

The U.S. transmission network is broken up into three main sections, or Interconnections, as indicated in the map below. Each Interconnection is operated largely independently, with minimal transfers of electricity between them. Each interconnection represents a single extremely large machine, with homes in Florida connected to the same network as homes in Toronto.

Map of the U.S. transmission system

Balancing Authorities in the Eastern & Western Interconnections

The Eastern and Western Interconnections are each subdivided into smaller Balancing Authorities, as indicated in the map below.

Each Balancing Authority has grid operators who maintain the balance of electricity supply and demand in that area and regulate exchanges of electricity with neighboring areas. Some Balancing Authorities are quite large, such as PJM, which serves 60 million customers in 13 Mid-Atlantic and Great Lakes states, while others are very small, serving an individual town. In a large balancing area such as PJM, an increase in electricity demand caused by someone turning on their lights in Chicago can be accommodated by a power plant increasing its output in New Jersey. In general, larger balancing areas are more efficient and allow for easier integration of renewable generation like wind energy, as the pool of resources on the system is larger and changes in output at one wind plant can cancel out opposite changes at another wind plant elsewhere on the system. In addition, there can be costs for moving electricity from one Balancing Authorities to another.

Map of balancing authorities in the eastern and we

Consumer savings result from a strong transmission system

Like the interstate highway or the nation’s rail network, the transmission network allows consumers to purchase lower cost energy that can be provided from other regions, instead of being dependent on electricity that is produced locally.

Having a robust transmission grid is also essential for ensuring that electricity markets remain competitive, as a power plant located in a part of the power grid with limited transmission ties to the rest of the grid can charge monopoly prices for its power, as there is limited competition. For this reason, many regions, including Texas, have put transmission cost allocation policies in place to ensure that a strong transmission system can be built.

Other transmission and integration resources