A switchyard is the set of facilities outside a power plant in which voltage is transformed and electricity flow is directed onto transmission lines. The switchyard comprises transformers plus a series of large switches, breakers, and other protective devices that can usually be manually or remotely opened and controlled to energize or de-energize specific transmission circuits leaving the plant. To disconnect a transmission line leaving the plant, the appropriate switches or breakers are opened in the switchyard at the plant. To connect a line the same switches or breakers are closed.

Many switchyards contain a station bus that serves as a convenient point to make modular connections in the future if more transmission lines are installed. The station bus commonly consists of a series of busbar or bus duct – high-power conductors commonly used in switchyards and substations to carry large amounts of power. The point where power is transferred from the power plant to the transmission line is often referred to as a station bus. 

A switchyard at a hydro power plant