A structure, usually a small building on a fenced-off lot, that contains any combination of routing or cutoff switches, transformers, surge arresters, capacitors, power conditioners and other equipment needed to insure smooth, safe flow of current. Substations are most commonly seen in residential and industrial areas, where one or more high voltage lines can often be feeding into the station and any number of lower-voltage distribution lines spider out to serve customers in the surrounding area.

One of the primary purposes for residential and industrial substations is the maintenance of proper line voltage in distribution systems, which insures proper line voltage for end-use customers. Electricity typically travels over high-tension lines and through underground cables at very high voltage, and transformers must be used at substations to convert this voltage to a lower voltage suitable for use by the consumer. The energy flow may require additional filtering to reduce its tendency to create magnetic fields or produce unwanted effects when used by sensitive electronic devices.

Producers of energy may maintain their own equipment near generating facilities for converting voltage and managing power distribution, but these facilities are typically not referred to as substations.

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