Electrical substation

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Figure 1. A large-scale electrical substation.[1]

Electrical substations are the interface between parts of the distribution grid and transmission systems. These fenced off areas (see Figures 1 and 2) step down the voltage in the transmission lines to one that is suitable for the distribution grid. They are also equipped with circuit breakers to protect the distribution system, and can be used to control the flow of current in various directions.[2][3] They also smooth and filter voltage fluctuations caused by, for example, an increased load.[4]


Figure 2. A common type of electrical substation seen in and around cities.[5]

Transformers lower the very high transmission voltages into a voltage less than 10 000 volts, which is suitable for distribution systems. Substations are also often equipped with a bus that splits off the current in multiple directions, as well as circuit breakers and switches which will allow the isolation and direct control of certain parts of the transmission and distribution systems.[2] Many substations also include capacitors to smooth the voltage output.


Substations can be categorized by their various functions and roles.

  • Step-down substation - These facilities lower the voltage from transmission lines to what is known as a subtransmission voltage, which is sometimes used for industrial purposes. Otherwise, the output is then directed to a distribution substation.[6]
  • Distribution substation - These substations further lower the subtransmission voltage to one that can be used to supply most industrial, commercial, and residential needs, with the aid of a distribution transformer before power is finally delivered to the load.[6] These facilities are sometimes located underground. Visit distribution grid for more information.

For Further Reading

For further information please see the related pages below:


  1. David Neale [CC BY-SA 2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons
  2. 2.0 2.1 Brain, Marshall, and Dave Roos. (Accessed July 28, 2015). How Power Grids Work [Online], Available: http://science.howstuffworks.com/environmental/energy/power.htm
  3. Alstom. (July 28, 2015). What is an electric substation? [Online]. Available: http://www.alstom.com/grid/about-us/understanding-electrical-grids/What-is-an-electric-substation/
  4. Enmax. (Accessed July 28, 2015). Substations [Online], Available: https://www.enmax.com/generation-wires/transmission-and-distribution/our-system/substations
  5. "Electrical Substation" by Wtshymanski at en.wikipedia - Licensed under Public Domain via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Electrical_Substation.JPG#/media/File:Electrical_Substation.JPG
  6. 6.0 6.1 6.2 United States Department of Labor. (Accessed July 28, 2015). Illustrated Glossary: Substations [Online]. Available:https://www.osha.gov/SLTC/etools/electric_power/illustrated_glossary/substation.html

Authors and Editors

Gokul Dharan, Jordan Hanania, Kailyn Stenhouse, Jason Donev
Last updated: September 3, 2018
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