Carbon-Pros Analyst Blog

The U.S. bulk power system has evolved into three major interconnected systems (power grids), within which regional transmission organizations and independent system operators exist to operate transmission systems. They also manage organized competitive markets for the purchase and sale of wholesale electricity. The major networks consist of extra-high-voltage connections between individual utilities designed to permit the transfer of electrical energy from one part of the network to another. These transfers are restricted, on occasion, because of a lack of contractual arrangements or because of limited transmission capability. The three networks are:

• the Eastern Interconnected System,
• the Western Interconnected System, and
• the Texas Interconnected System.

The Texas Interconnected System is not interconnected with the other two networks (except by certain direct current lines). The other two networks have limited interconnections to each other. Both the Western and the Texas Interconnect are linked with different parts of Mexico. The Eastern and Western Interconnects are completely integrated with most of Canada or have links to the Quebec Province power grid. Virtually all U.S. utilities are interconnected with at least one other utility by these three major grids. The exceptions are in Alaska and Hawaii. The bulk power system makes it possible for utilities to engage in wholesale (sales for resale) electric power trade. Wholesale trade has historically played an important role, allowing utilities to reduce power costs, increase power supply options, and improve reliability. Historically, most wholesale trade was between interconnected utilities within the continental United States. With open access and deregulation of wholesale markets cross-border trade has become more prominent in meeting domestic electricity requirements. U.S. international trade is mostly imports. Normally, most imports are from Canada, with a small portion coming from Mexico.

Source: Energy Information Administration (EIA)