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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.

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56 Comments


  1. Nissi Engineering Solution
    May 10, 2019

    Great! Thanks for sharing this information I am very happy to read this content. It is very useful and informative.


  2. Anoop Kumar Sharma
    Apr 25, 2019

    Can we consider one VCB with metering and protection system for one transformer?


  3. Alfredo Padamo
    Mar 13, 2019

    Good Morning
    I thank you for the conversion of 800KVA -22kv cooling onan 3 phase 50hz vector group DYN11


  4. Mphumzi Kleinbooi
    Jan 24, 2019

    Good day sir/madam,
    I’m working for BCMM Municipality-electricity.Im a clerk of works here.i need you to help me understand the heavy current components,specificaly the substation equipment and each its components and use.Breakers,transformers,auxiliary transformers,isolators,current transformers,voltage transformers,surge arrestors,neutral earthing compensator(NEC),neutral earthing compensator resistor(NECR),HYpact unit Line,cubular bus bars and conductor bus bar.132 and 66kv bus couplers,HYpact bus coupler,132kv and 11kv bus section breaker,panels,DC system,DC supply for inverter.
    Thank for the assistance in advance.


  5. Willem du Toit
    Nov 07, 2018

    Thank you for an excellent portal where all can learn about Distribution networks.


  6. Javier Meza
    Aug 15, 2018

    I am looking for literature related with Substation Ground Grid Connectors for Below Grade Applications


  7. ADEKUNLE UTHMAN
    Aug 09, 2018

    Thanks for this opportuninity,now i understand more on power systems


  8. Sushanta Kumar Panda
    Jul 11, 2018

    Its really a best site to enhance knowledge and find out solution of many doubts. so I thanks to creator of this site .


  9. Samer Alsadi
    May 29, 2018

    very good site


  10. Balone
    May 23, 2018

    hello i am experiencing a 95% stator earth fault on my generator protection .relay its an REG670 please assit


  11. Ms Lee Wan Ling
    Apr 11, 2018

    Kindly quote to us building cost for 1 unit substation in industrial area of integrated oil and petrochemical refineries at Rapid PTD 5319 H.S.D 36874, Mukim Pengerang, Daerah Kota Tinggi, Johor, West Malaysia
    Kindly mention your lead time delivery.

    Thank you


    • hitesh arora
      Apr 24, 2018

      pls share ur email id.


  12. baseemnasir
    Jan 12, 2018

    Hello dear
    please i want to get the calculation design on a capacitores in electrical substation and and how can we calculate the size of capacitance to instull in electrical power system


  13. Manikandan
    Dec 18, 2017

    How to calculate the substation fault level and what are the inputs are required


  14. vijaya manikanta
    Dec 15, 2017

    Can we consider parallel runs in determining short circuit rating of feeder?

    Example: 33KV incoming feeder has to be designed for 33KV, 31.5KA, 1sec rated Panel to feed 20MW, feeder length is about 2000 m to be laid in RCC Trenches.

    2Runs 33KV, 300 Sqmm, AL Cond., XLPE Cable is recommended to cater 20MW, 350A & fault current of 31.5KA, 1 Sec.

    1Run of 300 Sqmm, AL Cond., XLPE Cable can carry 310A in duct @ 30 deg C and about 28KA for 1 sec as per manf. catalog.

    Considering De-rating Factors for temperature & grouping etc. actual capacity 237Amps/ Run

    So 2 runs cater 474 Amps i.e. more than sufficient to cater required 350A.

    As 2 Runs are considered it is supposed to cater 31.5KA, 1sec considering current sharing in parallel runs.

    Kindly give your advice on the above.


  15. AKRAM FLITI
    Dec 13, 2017

    PLZ can you help me to find a electrical engineering final year project .

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