Notes

Aluminium Windings - Dry Type Transformers 

By on

The other day I was talking to a colleague who is a building services consultant.  Despite regularly specifying dry-type/cast resin transformers he was unaware that many manufacturers use aluminium for the windings; I think Siemens exclusively use aluminium and don’t offer copper anymore.  To confirm this he promptly phoned Schneider Electric and was informed that they use aluminium (or copper on request).

This reminded me of a few years ago when I was working for a contractor and wanted to install Siemens transformers on a large international airport.  Siemens was one of the three preferred vendors; however the airport’s specification called for copper windings.  Because of the specification the airport refused the transformers for weeks (we even had the Siemens factory guys out from Germany).  The client’s agreement in the end was not driven by technical considerations, but by contractual/time delay issues.  Transformers were installed and as far as I know are still happily humming away.

The illustration of a Siemens GEAFOL transformer shows the HV and LV aluminium windings.  The HV windings are wound from aluminium foil interleaved with an insulating foil.  The LV windings are wound form single-aluminium sheets and interleaved with cast-resin impregnated fibreglass fabric. Foil type windings are subject to less electrical stress than conventional windings resulting in higher AC and impulse voltage withstand characteristics.  Thermal expansion coefficients of aluminium and cast resin are similar and resulting thermal stress due to load change is kept to a minimum.

To my mind, compliance with the performance requirements of the manufacturing standards is the important criteria and the constructional aspects (aluminium or copper) are not that significant. As a final practical tip, during the above airport installation copper cable was being terminated onto the aluminium terminals of the transformer.  In this instance bi-metallic plates were inserted between the cable lugs and transformer terminals.

, ,

More interesting Notes:
Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus

View 6 Comments (old system)

  1. ManjoloPhiri's avatar ManjoloPhiri says:
    9/1/2011 2:11 PM

    The only reason I would allow the use of Alluminium windings in a transformer is the price difference between copper and alluminum. Copper is the best material so far for transformer windings whatever electrical parameters you consider! Please transformer manufacturers continue using copper afterall the price is now down!

    • Steven's avatar Steven says:
      9/1/2011 2:11 PM

      My aluminium winding experience has been with Siemens because they only manufacture aluminium windings. Have to say that I have never had any problems and the transformers work great. Of course copper windings also work great (to me both are acceptable). Talking of problems and a bit off topic, I also think that when selecting a transformer it needs to be suitable for the intended environment/loading and that surge arrestors if used are correctly sized. I have recently come across an instance where this was not done and they have had several transformer failures.

  2. rommel's avatar rommel says:
    9/1/2011 2:11 PM

    Which material, element is more conductive? copper or aluminium?

    • Steven's avatar Steven says:
      9/1/2011 2:11 PM

      Copper is the better conductor. Although Aluminum is still pretty good as a conductor.

  3. Paul's avatar Paul says:
    12/28/2012 2:57 PM

    How the bi-metallic plates can eliminate the ionization potential between two type of metal?

    • Steven's avatar Steven says:
      1/13/2013 7:41 AM

      Bimetallic plates prevent corrosion which could result from a direct connection of two dissimilar metals (aluminum and copper in this case).

Comments are closed for this post:
  • have a question or need help, please use our Questions Section
  • spotted an error or have additional info that you think should be in this post, feel free to Contact Us
Why use catalogues

I'm a fan of using manufacturers catalogues. There are two main reasons for this. Firstly, if your involved in the purchase of equipment, you will likely...

Fault Calculation - Symmetrical Components

For unbalance conditions the calculation of fault currents is more complex. One method of dealing with this is symmetrical components. Using symmetrical...

Maxwell's Equations - Gauss's Electric Field Law

Gauss's Electrical law defines the relation between charge ("Positive" & "Negative") and electric field.  The law was initially formulated by Carl Friedrich...

Always Use PPE

A lot of our members work in countries where PPE (personal protective equipment) is regulated or they work for companies/organizations which take employee...

Tip – Latitude and Longitude on Large Scale Plans

If you are working on a large plan, get the real coordinates [latitude, longitude] for two or more points and add them to the drawing. That way you can...

How to Check a Circuit is Dead

If you want to check a circuit is dead (not live), you should always use the three point method. First check a known live circuit, then check the dead...

Introduction to Current Transformers

Current transformers (CTs) are used to convert high level currents to a smaller more reasonable level for use as inputs to protection relays and metering...

Star-Delta Motor Starting - Performance

Many questions sent in to the site are in connection with motor starting and in particular star-delta.  For all but the simplest application, there is...

Questions - Reputation and Privilege

Our question and answer system while letting you do exactly what it says, is much more.  It is a dynamic user driven system, where our users not only ask...

Write your best report

Years ago I was told that you should always try to write the best report you can.  Many years later I still think on this as one of the better pieces of...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note. 

Footer
(click here to extend)
Copyright (c) 2026 myElectrical