This balance is needed to maintain the safe and reliable operation of the power system. ERCOT is unique in that the balancing authority, interconnection, and the regional transmission organization are all the same entity and physical system.Ī balancing authority ensures, in real time, that power system demand and supply are finely balanced. All of the regional transmission organizations in the United States also function as balancing authorities. Most, but not all, balancing authorities are electric utilities that have taken on the balancing responsibilities for a specific portion of the power system. The actual operation of the electric system is managed by entities called balancing authorities.
These interconnections describe the physical system of the grid. This redundancy helps prevent transmission line or power plant failures from causing interruptions in service. The network structure of the interconnections helps maintain the reliability of the power system by providing multiple routes for power to flow and by allowing generators to supply electricity to many load centers.
The Electric Reliability Council of Texas (ERCOT) covers most, but not all, of Texas and consists of a single balancing authority. The Western Interconnection encompasses the area from the Rockies west and consists of 37 balancing authorities: 34 in the United States, 2 in Canada, and 1 in Mexico. The Eastern Interconnection consists of 36 balancing authorities: 31 in the United States and 5 in Canada. The Eastern Interconnection encompasses the area east of the Rocky Mountains and a portion of northern Texas. At the highest level, the United States power system in the Lower 48 states is made up of three main interconnections, which operate largely independently from each other with limited transfers of power between them. Local electricity grids are interconnected to form larger networks for reliability and commercial purposes. In the United States, the power system consists of more than 7,300 power plants, nearly 160,000 miles of high-voltage power lines, and millions of low-voltage power lines and distribution transformers, which connect 145 million customers. The sizes of the circles are roughly indicative of electric system size.Įlectricity generated at power plants moves through a complex network of electricity substations, power lines, and distribution transformers before it reaches customers. Energy Information Administration Note: The locations of the electric systems are illustrative and are not geographically accurate. Circuit length refers to the sum of the route length of each circuit on a line.Ģ.Due to the Accounting Rules for Electricity Business amendment (effective from March 29, 2000), distribution facilities with voltage over 20 kV have been included in transmission facilities since FY1999.ģ.The sum is not equal to a total of breaskdown due to rounding.Source: U.S. 
The combined circuit lengths of overhead and underground transmission lines total approximately 40,000 km, which is equivalent to the circumference of the earth.ġ.Route length refers to the total length between two points on a line (horizontal length between supports).
Overhead transmission lines consist of a route length of 14,781 km and circuit length of 28,365 km, with 50,369 supports, while underground transmission lines consist of a route length of 6,391 km and circuit length of 12,325 km. The table shown below indicates the amount of equipment in use at the end of FY2016. Circuit Lengths of Overhead and Underground Transmission Lines
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