An power substation is a subsidiary station of an electricity generation, transmission and distribution system where voltage is transformed from high or medium to low or the reverse using transformers. Electric power flows through several substations between generating plant and consumer changing the voltage level in several stages.
A substation that has a step-up transformer increases the voltage with decreasing current, while a step-down transformer decreases the voltage with increasing the current for domestic and commercial distribution. The word substation comes from the days before the distribution system became a grid.
At first substations were connected to only one power station where the generator was housed and were subsidiaries of that power station.
Elements of Substation
Substations generally contain one or more transformers and have switching, protection and control equipment. In a large substation, circuit breakers are used to interrupt any short-circuits or overload currents that may occur on the network. Smaller distribution stations may use re-closer circuit breakers or fuses for protection of branch circuits. A typical substation will contain line termination structures, high-voltage switchgear, one or more power transformers, low voltage switchgear, surge protection, controls, grounding (earthing) system, and metering. Other devices such as power factor correction capacitors and voltage regulators may also be located at a substation.
Substations may be on the surface in fenced enclosures, underground, or located in special-purpose buildings. High-rise buildings may have indoor substations. Indoor substations are usually found in urban areas to reduce the noise from the transformers, to protect switchgear from extreme climate or pollution conditions.