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Substation theory and practice

An electrical substation is a subsidiary station of an electricity generation, transmission and distribution system where voltage is transformed from high to low or the reverse using transformers. Electric power may flow through several substations between generating plant and consumer, and may be changed in voltage in several steps.

Power substation guides, research papers and studies
Power substation guides, research papers and studies (on photo: Ghana Aboadze 330kV substation)

A substation that has a step-up transformer increases the voltage while decreasing the current, while a step-down transformer decreases the voltage while increasing the current for domestic and commercial distribution. 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 the generator was housed, and were subsidiaries of that power station.


Equipment in substation

Substations generally have switching, protection and control equipment and one or more transformers. 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 recloser circuit breakers or fuses for protection of distribution circuits. Substations do not usually have generators, although a power plant may have a substation nearby.

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 several indoor substations. Indoor substations are usually found in urban areas to reduce the noise from the transformers, for reasons of appearance, or to protect switchgear from extreme climate or pollution conditions.

Where a substation has a metallic fence, it must be properly grounded (UK: earthed) to protect people from high voltages that may occur during a fault in the network.

Earth faults at a substation can cause a ground potential rise. Currents flowing in the Earth’s surface during a fault can cause metal objects to have a significantly different voltage than the ground under a person’s feet; this touch potential presents a hazard of electrocution.

Browse guides and papers

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61 Comments


  1. [email protected]
    Feb 04, 2023

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    May 11, 2022

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  3. Igwe Geoff
    Aug 05, 2021

    i thank you for your desire to extend knowledge.
    Please i am working on an estate that has 64Nos 500kva 11/415kv transformers.
    I divided the transformers into four radial circuits.

    One of the circuits has 26Nos 500kva transformers. Can i use 3 x150mm2 aluminium conductor to connect them considering that cureent for 26Nos 500kva is 679A


  4. Igwe Geoff
    Aug 05, 2021

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    I have 27 transformers of 500kva to be feed from a sf6 1250A.
    Can i use 150mm2 aluminium conductors to feed the transformers in radial form


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    Jul 14, 2021

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  8. B.H. Merzayi
    Jun 03, 2020

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    • Igwe Geoff
      Aug 05, 2021

      i thank you for your desire to extend knowledge.
      Please i am working on an estate that has 64Nos 500kva 11/415kv transformers.
      I divided the transformers into four radial circuits.

      One of the circuits has 26Nos 500kva transformers. Can i use 3 x150mm2 aluminium conductor to connect them considering that cureent for 26Nos 500kva is 679A


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