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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

Note that all documents in this section are free to download. Navigate through sub-pages to discover all documents.

Static Analysis of Power Systems

A power system consists of generation sources which via power lines and transformers transmits the electric power to the end consumers. The power system between the generation sources and end… Read more

May 03, 2014

Transmission system in north-western Europe

The 21st Century Substation Design

An electrical substation is a part of an electricity generation, transmission and distribution system where voltage is transformed from high to low or in reverse using transformers. It also serves… Read more

Jan 18, 2014

The 21st Century Substation Design

Improving safety on ageing switchgear

Retrofitting is defined as adding components to equipment on site so as to achieve additional features or ratings. A number of different retrofitting options are available that will improve the…...

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Jan 05, 2014

Energy transmission and distribution guide

The purpose of the electric transmission system is the interconnection of the electric energy producing power plants or generating stations with the loads. A three-phase AC system is used for… Read more

Nov 30, 2013

Standing side by side - two significant role players in the supply of energy

Measuring Earth Resistance

First, the NEC code requires a minimum ground electrode length of 2.5 meters (8.0 feet) to be in contact with soil. Soil composition, moisture content, and temperature all influence the… Read more

Sep 27, 2013

Measuring Earth Resistance

Safety operations on medium voltage switchgear

There are five types of hazards associated with the operation of electrical equipment: electrical shock, electrical burns, fire and explosion, heat build up and mechanical hazards. Let’s briefly describe each… Read more

Jun 08, 2013

Safety operations on medium voltage switchgear

59 Comments


  1. 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


  2. Igwe Geoff
    Aug 05, 2021

    I am working on an an estate that have 65 Nos 500kva 11/415 transformers.
    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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    • 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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