Electricity transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines which facilitate this movement are known as a transmission network. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. The combined transmission and distribution network is part of electricity delivery, known as the electrical grid.  Increasingly microgrids are being established to serve a discrete geographic footprint, such as a business complex, college campus, hospital center, or neighborhood. Within microgrids are one or more kinds of distributed energy resources are established to produce power, e.g. solar panels, wind turbines, generators and batteries.

Efficient long-distance transmission of electric power requires high voltages. This reduces the losses produced by heavy current. Transmission lines mostly use high-voltage AC (alternating current), but an important class of transmission line uses high voltage direct current. The voltage level is changed with transformers, stepping up the voltage for transmission, then reducing voltage for local distribution and then use by customers.

A wide area synchronous grid, also known as an “interconnection” in North America, directly connects many major generation plants that are delivering alternating power with the same relative frequency to many locations within a geographic range. For example, there are four major interconnections in North America (the Western Interconnection, the Eastern Interconnection, the Quebec Interconnection and the Electric Reliability Council of Texas (ERCOT). In Europe one large grid connects most of continental Europe.

Historically, transmission and distribution lines were often owned by the same company, but starting in the 1990s, many countries and states with countries have liberalized the regulation of the electricity market in ways that have led to the separation of the electricity transmission business from the distribution business.

Natural gas transmission is the highly integrated pipeline network that moves natural gas throughout the continental United States. The pipeline network has about 3 million miles of mainline and other pipelines that link natural gas production areas and storage facilities with electricity generation plants or directly to industrial, commercial and residential consumers.

Transporting natural gas from production areas to electricity generation plants and to industrial, commercial and residential consumers involves a series of steps that are generally carried out in the following order:

  • Gathering systems, primarily made up of small-diameter, low-pressure pipelines, move raw natural gas from the wellhead to a natural gas processing plant or to an interconnection with a larger mainline pipeline.
  • Natural gas processing plants separate hydrocarbon gas liquids, nonhydrocarbon gases, and water from the natural gas before the natural gas is delivered into a mainline transmission system.
  • Wide-diameter, high-pressure interstate transmission pipelines that cross state boundaries and intrastate transmission pipelines that operate within state boundaries transport natural gas from the producing and processing areas to storage facilities and distribution centers. Compressor stations (or pumping stations) on the pipeline network keep the natural gas flowing forward through the pipeline system.
  • Local distribution companies deliver natural gas to consumers through small-diameter, lower pressure service lines.

In the future delivery of natural gas will increasingly be directed to distributed energy resources, i.e. natural gas fired generators, which will generate electricity and deliver to a microgrid that serves a discrete geographic footprint, such as a business complex, college campus, hospital center, or neighborhood.