An aerial substation
A substation is the part of an electricity transmission and distribution system where voltage is transformed from low to high and vice versa using transformers. The range of voltages in a power system vary from 110 V to voltages of up to 765 kV. Transformation may take place in several stages and at several substations in sequence, starting at the generating plant substation where the voltage is increased for transmission purposes and is then progressively reduced to the voltage required for household use.
The word substation comes from the days before the distribution system became a grid. The first substations were connected to only one power station, where there was the generator, and were entirely dependent on it, hence the name.
Substations may be on the surface in fenced enclosures, underground, located in special-purpose buildings, located on power poles (aerial substations) or located in the service areas of the buildings they service. Substations located within the buildings they serve are particularly a feature of high-rise buildings.
It is more efficient to transmit electricity over long distances at very high voltages; the function of the substation is to reduce the voltage to a more manageable, and for domestic use, safer level.