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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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