Premium Membership ♕

CYBER MONDAY OFFER 💥 Save 20% on PRO Membership Plan and Video Courses with the coupon CYM23 and learn from experienced engineers.

Home / Technical Articles / Power Distribution Network Explained To Electrical Engineers (Beginners)

Primary distribution voltages

In the UK, voltages of 132 kV, 110 kV, 66 kV, 33 kV and 11 kV are typically used to provide primary distribution, with a 380–415 V three-phase and neutral low voltage supply to smaller consumers, such as residential or smaller commercial premises, where 220–240 V single-phase to neutral is taken off the three-phase supply.

Power Distribution Network Explained To Electrical Engineers (Beginners)
Power Distribution Network Explained To Electrical Engineers (Beginners) - photo credit:

An example of a three-phase power distribution network is illustrated in Figure 1 below.

3-Phase Power Distribution Network

Distribution voltages in continental Europe are typically 110 kV, 69 kV and 20 kV, but practice varies from country to country. In the USA, voltages of 138 kV, 115 kV, 69 kV, 34.5 kV, 13.2 kV and 4.16 kV are employed.

Power distribution network
Figure 1 – Power distribution network (click to expand image)


The transformer stepping down from the primary distribution to the low voltage supply may be pole-mounted or in a substation, and it is close to the consumers in order to limit the length of the low voltage connection and the power losses in the low voltage circuit.

In a national power system, many thousands of transformers and their associated circuit breakers or fuses / protective devices are required for distribution to low voltage circuits, in contrast to high-voltage transmission and primary distribution systems, where the number of substations is in the hundreds.

Three-phase pole mounted distribution transformer
Three-phase pole mounted distribution transformer (credit:

The progressive introduction of small-scale distributed generation (DG) is now a major issue for distribution networks.

These networks, which have been designed for one-way-traffic of energy from transmission levels down to consumers, may have to be modified to accept the possibility of reversed flow caused by the DG exceeding local demand. This has a significant impact on the protection systems required.

It will be noted from Figure 1 that the primary and low voltage distribution systems are connected in a radial configuration. Circuit loops between adjacent substations are avoided because these can lead to circulating currents, which may increase the power losses and create difficulty in protection schemes.

However, tie circuits between adjacent lines and cables are available to reconfigure the network when a portion of the low voltage circuit is out of service for maintenance or because of failure.

These tie circuits are controlled by a normally open switch which can be closed manually within a few minutes, although an increasing trend is for automation of this operation by Supervisory Control and Data Acquisition (SCADA) systems.

Urban and suburban areas

In urban and suburban areas, much of the primary and low voltage distribution system is underground, with readily accessible substations sited in cellars or on small secure plots. Industrial sites may also have a number of substations incorporated into buildings or secure areas.

These may be controlled by the works engineer or operated and maintained by an electricity distribution company.

Rural areas

In rural areas and in more dispersed suburban areas, many three-phase overhead lines operating at 10-15 kV or 27-33 kV are supported for many miles on poles which may be of wood, concrete or steel lattice. The 380–415 V three-phase supply is taken from these lines through a small pole-mounted fused input/output transformer.

If the maximum load to be taken is below about 50 kW, the supplies for homes or farmsteads may be derived from a single-phase 10–15 kV supply.

Typically, a rural primary distribution system supplies up to 50 step-down transformers spread over a wide region. The lines in such a system are vulnerable to damage by tree branches, snow and ice accumulation and lightning strikes and it therefore has lower reliability than underground systems in urban areas.

Rural distribution power substation
Rural distribution power substation

Considerable ingenuity has been applied to protection of this type of system with the use of auto-reclosing supply circuit breakers and automatic reconnection switches.

It is now a common practice in developed countries to monitor the primary distribution system down to 10–15 kV and to display alarm, voltage and power-flow conditions in a control room. And in the event of an incident, repair crews are despatched quickly.

Repairs to the low voltage system are still dependent, however, on consumers notifying a loss of supply.

Earthing of distribution systems

The proper earthing of distribution systems is of prime importance in order that excessive voltages do not appear on connections to individual consumers.

It is the practice in UK and some other countries to connect to earth the neutral conductor of the four-wire system and the star point of the low voltage winding on the step-down transformer, not only at the transformer secondary output, but also at every load point with a local meter and protective fuse.

Protective Multiple Earth (PME) system
Protective Multiple Earth (PME) system – photo credit:

This is known as the Protective Multiple Earth (PME) system, which is designed to ensure that all metallic covers and equipment fed from the supply are bonded so that dangerously high voltages do not hazard lives.

Reference: Newnes Electrical Power Engineer’s Handbook – D.F. Warne (Purchase hard copy from Amazon)

Premium Membership

Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It helps you to shape up your technical skills in your everyday life as an electrical engineer.
More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Menbere Alemu
    Dec 20, 2022

    Hello Dear all Members of the Group.
    please add me in your group members.
    I’m Electrical engineers from Ethiopia.

  2. Olatunji Adeyemi
    Aug 08, 2022

    Thank Edvard, your article on power distribution is very concise and easy to understand even for a non electrical engineering person like me that works in electrical engineering industry.

    Thank you for sharing this invaluable knowledge!

    Olatunji Adeyemi
    from Abu Dhabi, UAE

  3. amaru woiza wolebo
    Dec 23, 2020

    hello guys how are you? i am fine and i written this message from Ethiopia electrical and computer engineering department and i will ask you one introduction electrical distribution network review paper design figure Microsoft vision word! please! help me guys

  4. YUNUSA Yakubu
    Aug 26, 2020

    Above explanation is a captivating picture of the power flow to the consumer for the young engineers’ attention. It contains alot field experiences and design information. We appreciate your kind effort because it will go a long way…. Thank you very much.

    • Mubbala Brian
      Dec 17, 2022

      Thanks alot Eng. Edvard for always providing us with the best Electrical Engineering Resources and we appreciate you so much for all your efforts in making sure that everything here is updated and true,
      Be blessed so much.
      I rank you excellent in making this a right place for us all to obtain quality knowledge and skills,
      Thanks alot,
      Merry Christmas to everyone here,

  5. Onesmus
    Jul 10, 2019

    Thank you for this article it is so helpful .

  6. Salim
    Jan 26, 2019

    Really great and big thanks to Mr Edvard. It hellped me alot

  7. Amp Authority
    Dec 20, 2017

    Great article. This is really helpful. We recently wrote about pin and sleeve as it relates to power distribution in a three phase system.

  8. Arun
    Dec 17, 2017

    Thanks a lot Edvard. U r really doing a great job. Sharing knowledge in a simple and effective way and it helps a lot of aspiring engineers in the world. Keep the good work. U r a teacher for many. Respect ??

  9. Johann A Myburgh
    Jul 16, 2017

    Great, practical and handy articles Edvard. Thank you, Johann Myburgh, Auckland, New Zealand

  10. bayoulath
    Dec 25, 2016

    Moi personnellement j’ai vos performances ,car cela me ramène à réussiccité là technologie numérique qui est dans moi

  11. Geoffrey
    Dec 24, 2016

    Thanks for writing this article, nice clear information with helpful videos.

  12. Alan Hetherington
    Jul 03, 2016

    I,m really enjoying the articles and especially the video presentations.I have recently got into needing to know electrical theory and its uses as I,m from a mechanical background so easy to understand from beginner level is very useful. Please keep up the great work.

Leave a Reply to Olatunji Adeyemi

Tell us what you're thinking. We care about your opinion! Please keep in mind that comments are moderated and rel="nofollow" is in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Let's have a professional and meaningful conversation instead. Thanks for dropping by!

4  ×    =  eight

Learn How to Design Power Systems

Learn to design LV/MV/HV power systems through professional video courses. Lifetime access. Enjoy learning!

Subscribe to Weekly Newsletter

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and guides (PDF).
EEP Academy Courses - A hand crafted cutting-edge electrical engineering knowledge