Al or Cu transformer windings? What’s your choice?

Copper or Aluminium Cast resin transformers?
What’s your choice?

Originally all transformers were built with windings made of copper. This prestigious conductor was easily accessible and its cost was not excessive.
The outbreak of the Second World War and a huge demand for copper by the military industry caused copper to disappear from the market and increase its price disproportionately. Transformer manufacturers have had to adapt to the market situation by using an alternative conductor, i.e. aluminum.
The first experiments were not particularly successful, but with time and by carrying out all the appropriate modifications of the transformer design, the aluminum proved to be an excellent conductor with the same copper characteristics. The first AL strips were used already in the 60’s in the USA and successfully largly accepted and utilized by European transformer manufacturers.
Power Sp. z o.o. is offering both Cu and AL cast resin transformers according to the clients needs. In case of distribution transformers and small power transformers we mostly work with Al conductor. For special projects like mines or in case of large power transformers we offer our clients Cu windings.
The choice of conductor material depends on many important aspects such as the use (type of application) of the transformer, the size and weight allowed, the budget available and the availability and delivery times of the transformer. Let see tha main positive and negative aspects of both conductors in case of application in cast resin transformers.


  • Excellent electrical conductivity
  • Excellent thermal conductivity
  • Excellent electrical and mechanical features in case of huge power transformers
  • Compact form (small dimension)
  • Excellent Streight & reduced physical expansion


  • High and variable price subject to speculations
  • Limited reserves  available
  • High weight
  • Different expansion values between Cu and cast resin by extremly low temperature may lead to cracks on the coil.
  • Reduced malleability during the winding process


  • Low and stable market price
  • Lower weight compare to Cu winding
  • Excellent malleability during the winding process
  • Very suitable for distribution transformers and small power transformers
  • Similar expansion values between Cu and cast resin by extremly low temperature


  • Less efficient thermal and electrical conductivity compare to Cu
  • Larger dimensions compare to Cu
  • AL external connections are not suitable in case of installation in mines or similar environments due to possible chemical reaction with gas or corrosive substances.
  • Constructive limits using Al. conductor by huge power transformers
  • In case of copper connectors special bi-metal plates are required (connection Al-Cu)

There are many technicians, including come copper transformer manufacturers, who believe that copper windings are more resistant to short circuit effects. They also claim that transformers with aluminum windings have significantly higher losses than copper transformers.
We have to dispel these claims. Based on our design and production experience, there are no differences in losses or short circuit resistance. Our aluminium transformers are designed and studied with an innovative design and electrical and mechanical solutions capable of guaranteeing the same level of losses and excellent electrical and mechanical strength as a copper transformer.
We are convinced that there are applications as distribution transformers, where it no longer makes sense to use copper as a conductor. Copper distribution transformers are to heavy for installation in the modern structures and result an expensive choice.
In case of special applications we strongly advise our customers to choose copper as a conductor to guarantee the required performance.

For further information visit our website or get in touch with our Staff at office@powerfullstop.com

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Your Power Team