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Transformer selection for substation

Oil filled transformers must be used for all outdoor substation. Some indoor substations (e.g. most industrial applications) should use oil filled transformers unless contractor or the consumer specifies otherwise.

Commercial and industrial substation manual (design and construction)
Commercial and industrial substation manual – Design and construction (photo credit:

Dry type transformers should be used for indoor substations located in high rise buildings (commercial and large residential blocks) and other major buildings frequented by the public (e.g. Convention/Exhibition centres and major shopping complexes). Dry type transformers for other high fire risk applications may also be specified.

Special care must be taken when selecting dry type transformers to ensure they are not overloaded.

The transformer should be such as to supply the whole of the load by one transformer. However where the maximum demand exceeds 1000kVA, then provision for two transformers and associated switchgear must be allowed.

Indoor substation - Typical layout
Indoor substation – Typical layout (click to expand layout)

Transformer space & ventilation requirements

Substations must provide sufficient space and ventilation to accommodate 1500kVA transformers, ensuring sufficient ventilation is provided for future load, even though smaller units may be initially installed.

Oil filled transformers require an area of 2300 mm long x 1800 mm wide, and dry type transformers require an area of 2300 mm long x 1800 mm wide.

Transformers must be separated from walls, ventilation equipment and other obstructions by a minimum of 900 mm. Transformers must not be directly placed under ventilation duct openings. With the exception of fire damper trip wires (if required), no item of equipment, installation or obstruction is to be placed over a designated transformer space.

Natural ventilation is not adequate for indoor substations. Mechanical ventilation must be provided. Section 10 details ventilation requirements.

As a guide, one general arrangement has been provided for each style 3 of indoor substation. Provided all clearance and access requirements are maintained, other arrangements may be used. An Energex Planning Officer must approve any alternate arrangement. Outdoor substations must be arranged in accordance with the standard layouts provided.

Title:Design and construction manual for commercial and industrial substations by Energex
Size:20.8 MB
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Design and construction manual for commercial and industrial substations by Energex
Design and construction manual for commercial and industrial substations by Energex

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  1. Selcuk Tuna
    Jul 07, 2022

    Thank for useful information. I have just one comment on the working that “Specialist Care should be taken when selecting a dry type transformer for overloading”. This true. However depending Load conditions and requirement, dry transformers may be subject to overlodaing conditions in severek applications. Therefore a the term of Duty cycle as a conceptual approach to be refere as well. Regards

  2. Noel Kari
    Jul 07, 2022

    I really appreciate the knowledge sharing.

  3. Esmael embang
    Jul 07, 2022

    Thanks for all the knowledges you impart.
    May i request about the testing of transformer? Thank you very much

  4. kamal lochan sahoo
    Apr 17, 2020

    I have a 11/.440 kv, 25 kva, 3phase transformer for my domestic & commercial building, since 3years. But, till date my full load trivector meter has hardly touched 9-10 kw
    Now Iam thinking to replace the 25kva trafo to a lower rating DRY TYPE transformer
    Can u suggest any technically viable points , about feasibility of changes

  5. Machander
    Aug 18, 2019

    Electrical Switchgear
    And Industrial drives basics for diploma level study

    Jan 16, 2019

    Dear Sir,
    i will visit your website, i need electrical substation for our shopping mall. our capacity : 4000 kva, set up out site of shopping mall. my we chat no. +8801711107560 , please send me substation Details with price offer.

  7. Barrie Skinner
    Feb 21, 2017

    The photo seems odd as there are no fire wall separators. Which country is this?

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