Aluminum or Copper Transformers

Reluctance to the use of aluminum conductors is the result of the problems that were first encountered over 40 years ago when making inappropriate aluminum to copper wiring connections in the field. The problem was the formation of aluminum oxides, a resistive compound, in the electrical connection. Serious overheating of the connection resulted.  Problems were also discovered when aluminum wire was mechanically inserted into copper fittings; each metal having different rates of thermal expansion.  Aluminum is now standard in high and medium class power transformers, distribution transformers and high power magnetics.

  • Aluminum is the industry standard in lighting transformers in 90% of commercial and industrial facilities.
  • Aluminum conductors are commonly used in utility and industrial transformers.

Aluminum Benefits

  • Equivalent Performance when compared to Copper
  • Lower Capital Cost than Copper
  • More Attractive Payback & Return-on-Investment
  • Longer Life Expectancy than Copper
  • Field Proven Track Record
  • Cooler Operating Temperatures than Copper
  • Lower AC Costs

Physical Properties and Design Requirements

Conductivity – 61% compared to Copper
Aluminum conductors require 66% more cross sectional area than copper.

Density – 30% compared to Copper
Aluminum windings require 66% higher cross sectional area than copper but have half the winding weight of copper.

Thermal Conductivity – 68% compared to
Since the aluminum conductor’s cross sectional area is 66% larger, the aluminum conductor will have 11% more thermal conductivity than copper.

Heat Capability – 2.5 times higher than Copper
For the same heat applied, the temperature rise will be 2.5 times less on a per pound basis. Since the weight of aluminum is only half that of copper, aluminum will have a 16% lower temperature rise, resulting in a cooler transformer.

Coefficient of Expansion – Higher for Aluminum;
Negated by welding connections to like material (i.e. AL wire to AL bus bar) and using absorption connectors.

Oxidization – ALO2 is an insulator
No oxide forms when conductive grease is applied. The grease eliminates exposure to moisture and oxygen. In fact, this connection has a better lifetime outcome than a copper bus bar.

Thermal Cycling – Annealing
In addition to a lower temperature rise, aluminum windings will cool less rapidly than copper. There is no brittlizing of the conductors due to wide temperature ranges. Wire is annealed, not tempered, with no adverse physical affects.

Sound Aluminum Conductor Design Practices

Internal Conductor Terminations
Internal conductors must be welded to aluminum bus bars. This ensures lifetime connections.

Customer Terminations
Expandable ‘Belleville Washers’ allow for thermal expansion to be absorbed without compromising the integrity of the connection.

The application of conductive grease on the plated copper cable lug to aluminum bus bar interface ensures that no moisture or air will come in contact with these conducting surfaces to produce oxidization.

Cost / Design Perspective

  • Aluminum costs 70% less per pound than copper, while the weight of the required aluminum is 50% less than
  • Conductor cost is roughly 40% – 50% that of
  • Magnetics weight is approximately 5-10% less (most of the weight still is in the core).
  • Aluminum magnetics will typically operate
  • Aluminum is less reactive to varnishes and many other chemicals used in magnetic production, resulting in a longer life
  • Volumetrically, aluminum and copper designs are almost
  • Energy efficiency requirements are
  • Design practices are now well accepted, with units in operation for more than 40