Generation, Transmission, and Distribution
Three-phase electricity originates in a generating station that might be owned by a utility, an independent power producer (IPP), or, perhaps, on the premises of a facility. The transmission of electricity from an electric utility to local switchyards could be over high-tension lines owned by a conglomerate. In fossil-fired steam power plants, electricity is generated by the burning of a fuel in a boiler in order to generate steam at a relatively high pressure. In a nuclear power plant, heat is generated by a controlled nuclear chain reaction using fissionable fuel. The heat generated produces steam that is used to power steam turbines. A utility's distribution system reduces transmitted higher-voltage power and delivers that electrical power at a lower voltage to its retail customers. Lines on the high-voltage side of distribution transformers are called primary distribution lines, or simply "primaries." Low-voltage connections on distribution transformers are called secondary distribution lines or "secondaries.".