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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 not all documents in this section are free to download. Navigate through sub-pages to discover all documents.

Why is arc detection so important?

High-impedance arcs and corona generate high-frequency current pulses that ride on the lower-frequency wave of the applied test-current waveform. These pulses may have a frequency ranging from less than 30… Read more

Dec 08, 2012

Why is arc detection so important?

SF6 or Vacuum MV Circuit Breaker?

Approximately 35 years ago, in the mid 1960s, two new breaker technologies, one using SF6 gas and the other vacuum as its arc quenching medium, were introduced to the market…. Read more

Nov 23, 2012

MV Switching Devices Selection – ABB

Switchgear, switchgear installations and all devices installed in it for high voltage up to and including 52 kV are commonly referred to as “medium voltage”. Which one is better, Vacuum… Read more

Nov 04, 2012

Capacitor Application Issues

Capacitors must be built to tolerate voltages and currents in excess of their ratings according to standards. The applicable standard for power capacitors is IEEE Std 18-2002, IEEE Standard for Shunt Power Capacitors…. Read more

Oct 19, 2012

Capacitor Application Issues

High voltage techniques course

The potential benefits of electrical energy supplied to a number of consumers from a common generating system were recognized shortly after the development of the “dynamo” commonly known as the… Read more

Sep 23, 2012

High voltage techniques course

Uninterruptible Power Supply (UPS) Types

In the electrical system environment, power disturbances will occur. These can be caused by faults on the distribution system, the operation of nearby equipment, lightning strikes, normal utility operations, or… Read more

Sep 08, 2012

XLPE Underground Cable Systems

The three cables in a 3-phase circuit can be placed in different formations. Typical formations include trefoil (triangular) and flat formations. The choice depends on several factors like screen bonding… Read more

Aug 05, 2012

Industrial XLPE Underground Cables


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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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