The two most common types of substations are transmission substations and distribution substations.
Transmission substations
Transmission substations are found where electricity enters the power grid. Because the output from power generators – such as power stations or wind farms – varies in voltage (between 130 kilovolt (kV) and 400kV in the UK, and up to 600kV in the US) it must be converted to a level that suits its means of transmission.
Electricity is then commonly transmitted through the high-voltage, overhead power lines you see supported by electricity pylons and can travel vast distances. In the UK, these run at either 275kV or 400kV. Increasing or decreasing the voltage to suit will ensure that it reaches local distribution networks safely and without significant energy loss.
Distribution substations
The electricity is then routed from the transmission system into a distribution substation, which will lower the voltage – to around 11kV in the UK – so it can enter our homes and businesses at a usable level. This is carried through a distribution network of smaller overhead lines or underground cables into buildings at 240V.