The transmission of electrical energy is the massive movement of electric energy from a generation site, such as a power plant, to an electrical substation. The interconnected lines facilitating this movement are known as a transmission network. This is distinct from local wiring between high voltage substations and customers, which is typically referred to as electric power distribution. The combined transmission and distribution network is known as the "power grid" in North America, or simply "the network." In the United Kingdom, India, Malaysia and New Zealand, the network is known as "National Grid".
A wide area synchronous network, also known as "interconnection" in North America, directly connects a large number of generators that deliver alternating current with the same frequency relative to a large number of consumers. For example, there are four major interconnections in North America (Western Interconnection, Eastern Interconnection, Quebec Interconnection and the Texas Electric Reliability Council (ERCOT)). In Europe, a large network connects most of continental Europe.
Historically, transmission and distribution lines were owned by the same company, but since the 1990s many countries have liberalised electricity market regulation in ways that have led to the separation of the electricity transmission business from the distribution.