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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.


  1. [email protected]
    Feb 04, 2023

    HV substation tubular switch yard transformer and other electrical equipment design and specification shall be elaborated.

  2. Stephen Ochieng' Okello
    May 11, 2022

    I appreciate and love thy modest way of skills and knowledge sharing around here!

  3. 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

  4. 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

  5. Biswajeet Rout
    Jul 14, 2021

    Hi, I am a graduate student, working on distribution system automation and security to cyber threat. I must say that your content is so unique to explain the terminology and equipment. I am requesting you to make an document and AMI, SCADA and PMU. I hope this will help the community in a large extent. Thank you.

  6. Nanle bitrus
    Sep 14, 2020

    You really improve my ideas in power

  7. Rex Gasinore
    Jul 09, 2020

    Learn more to understand what is all about Electrical Technology..

  8. B.H. Merzayi
    Jun 03, 2020

    Hi dear!
    Please, send information about RTCC panel for a 110kV /20kv substation
    thank you.

    Mar 21, 2020

    i would like to be a regular contributor to most discussions in electrical engineering. Specifically in areas of protection, Reliability engineering and alternative energy. Am an electrical engineer by training with over 30 years of expereince both in the academic and industry.

    • 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

  10. Satish Bedi
    Jan 11, 2020

    i have lot of ideas for Electrical energy conservation which i had tested and result is good

  11. Godswill Essienta
    Aug 18, 2019

    you guys are unique, i want to be part of this vision, thanks.

    Aug 01, 2019

    hi am francis from bonum kenya limited
    kindly see your email and let me know what item you manufacture

  13. Agaba Emmanuel
    Jun 07, 2019

    I wish to subscribe to this portal,thanks

  14. 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.

  15. Anoop Kumar Sharma
    Apr 25, 2019

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

  16. Alfredo Padamo
    Mar 13, 2019

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

  17. 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.

  18. Willem du Toit
    Nov 07, 2018

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

  19. Javier Meza
    Aug 15, 2018

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

    Aug 09, 2018

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

  21. 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 .

  22. Samer Alsadi
    May 29, 2018

    very good site

  23. Balone
    May 23, 2018

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

  24. 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.

  25. 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

  26. Manikandan
    Dec 18, 2017

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

  27. 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.

    Dec 13, 2017

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

  29. Md. Ashraful Alom
    Oct 09, 2017

    I glade to see such a nice blog site i ever see…….and useful. Thanks again!

  30. A M Venkatesh
    May 31, 2017

    Been visiting this site for a pretty long time. Has been very useful whenever I was stuck in a problem / crisis concerning substation, distribution and transmission design engineering. Would like to contribute from my collections which will be useful to design engineers.

  31. Timothy Partasevitch
    Mar 17, 2017

    Hello, Mr. Csanyi, If you wouldn’t mind, while we are on the subject on the subject of Electrical Software, I would like to hear your opinion on custom software development for power networks. Seeing how the market is dominated by a particular number of companies, can outsiders (IT company) step in and be competitive.

    I’ve recently graduated and now I found myself in this particular business, directly connected with the marketing department. Although I can’t say much about details and particulars (NDA, I’m sure you understand), I work on adaptive coordination for overcurrent relays. I can share link to the particular article (it’s potential customer oriented, not purely technical), discussing the possibilities and advantages of implementing the adaptive OCR.

  32. Thabiso Boase
    Jan 24, 2017

    This site makes me a better person daily

    Jan 03, 2017


    Please, Can I find books about Photovoltaic systems / Substations?

    email: [email protected]

  34. Faysal
    Dec 31, 2016

    I will be benefited if you assist to know how to calculate HT CT ration for HT/VCB Panel.
    Thanks in Advance ….

  35. Qaisar Jamil Akhtar
    Apr 20, 2016

    Hi, i study your E E portal, That is good attempt to convey your syetem specs to Readers, pls i need substations details on my Email site.

    Thanks & Regards

  36. hossein
    Apr 05, 2016

    Hello my Friend.Could we omit the GCB(Generator Circuit Breaker) of a 160MW Combined Cycle unit (with a 160MW/15.75kV Genarator and a 200MVA/230/15.75kV Unit Transformer)?

  37. Saadat
    Mar 26, 2016

    How can i find the book “Substation Commissioning Training Course” written by Mr. Raymond Lee ??
    It is very Urgent.
    Thank you.
    My email: [email protected]

  38. zaya
    Dec 11, 2015

    Thank you,7

  39. sathish
    Aug 30, 2015

    I’m a substation supervisor in Bangalore.

  40. Nicks Mutuku
    Jul 13, 2015

    This quite helpful. Keep it up.

  41. Local Sydney Electricians
    Jul 03, 2015

    Using Voltage Stabilizer and UPS systems can prevent you from any kind of power mishaps.

  42. George
    Oct 23, 2014

    how to make electric motor solo run procedure

  43. Elvis Mulowa
    Jul 24, 2014

    thanks for the good works we are really updated

  44. letlhogonolo mogorosi
    Mar 27, 2014

    I am working as a technician in eskom, i like knowing about different protection we found in our substation,different relays how they operate when flacked what fault to be expected.more especially in distribution substations.i hope ill learn a lot from you thanks.if posible can you send me theorytical guardes.

  45. AIDIL ARIFIN, E Eng.
    Mar 21, 2014

    Thanks & Regards,

  46. B.Venkat Reddy
    Feb 16, 2014

    Excellent Technical Knowledge Site, I Like Very much and Many Thanks for providing such useful technical paper, keep the good works.

  47. cristian
    Jan 19, 2014

    Thanks for your documentations ,my job is electrical technician ,vendor position for italian provider LV & MV electrical equipment.


  48. Aljan24uson
    Oct 25, 2013

    Thanks for this kind of portal site. It is very informative and helps a lot to our fellow electrical practitioners….keep it up guys!!!

  49. DONDON
    Mar 03, 2013

    Can anyone show me the Fault Current Calculation of Transmission Lines?

  50. namnguyen
    Mar 02, 2013

    Thanks for useful technical paper, keep the good works.

  51. alhana89
    Jan 27, 2013

    Thanks for making these references available for us. Keep up the good work, guys!

  52. lollo
    Jan 08, 2013

    Hi the people iv just finished my studies and am currently working,and I have been learning on how to use the new software “Janitza GridVis software” and this software monitors power from High to Low voltage systems and currently i have been tasked yo write a programm that will be used for valves have any of you people got maybe some idea on this new jasic programming??

    • Edvard
      Jan 08, 2013

      To be honest I never heard of it. Can you share with me some information about it, some links.

  53. Rateb Fares
    Oct 25, 2012

    thank you very much

  54. Jones
    Jun 16, 2012

    kindly provide substation earth mat calculation …

  55. engrwaqas_11
    Nov 20, 2011

    thank you very much for such nice work..if possible please upload field testing date e.g. transformers testing, under ground cable testing, relays testing..etc


    Waqas Ahmed

  56. subhransu
    Nov 13, 2011

    want to be a part of this knowledge pool. Help me out.

    Aug 01, 2011


  58. diamond
    Jul 27, 2011

    thanks a lot

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