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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.

Complete Guide To Wind Power Plants

In the study of wind turbines injecting power into the grid, the last is often considered ideally with infinite short-circuit power. Therefore it cannot be influenced by the connection of… Read more

Jan 17, 2015

Complete Guide To Wind Power Plants

Instrument Transformers Application Guide

A current transformer is, in many respects, different from other transformers. The primary is connected in series with the network, which means that the primary and secondary currents are stiff… Read more

Oct 18, 2014

Instrument Transformers Application Guide

Transformer protection application guide

This guide focuses primarily on application of protective relays for the protection of power transformers, with an emphasis on the most prevalent protection schemes and transformers. Principles are emphasized. Setting procedures are only… Read more

Oct 11, 2014

Transformer Protection Application Guide

Thermal design of MV/LV substations

Among the type tests listed in the IEC 62271-202 standard, the temperature-rise test is no doubt one of the major tests used to validate the performance of prefabricated MV/LV substation… Read more

Sep 13, 2014

Thermal design of MV/LV substations

Substation Design Guidelines

The rating of substation equipment as well as the connections must be decided. Selection of transformers Ratings of circuit breakers Ratings of switch disconnecters (Load-break switches) Ratings of isolators (Disconnecters)… Read more

Jul 05, 2014

Substation Design Guidelines

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