Replacing aluminum conductors with copper conductors in power and distribution transformers up to 10 MVA
There are many transformers in use rated up to 10 MVA (10,000 kVA) that were originally wound using aluminum conductors. When damaged or when selected for rewind, the aluminum conductor is often replaced with copper conductor. This is usually fairly routine when the conductor changes are undertaken within the bounds of the original transformer design. It is this type of change that will be reviewed in this article. It is not the intent to provide information here for the complete redesign of the transformer. It is important that all coil dimensions remain as close to the originals as possible. In carrying out the type of change outlined above, there are some design issues and differences in material properties that must be considered before proceeding with the work. Some of these issues are:
- The effect that the difference in thermal characteristics of the materials will have on short term overload capability.
- The effect that the different material properties will have on the original blocking and bracing system.
- The effect that the difference in conductivity will have on conductor size.
- The effect that the difference in conductor size may have on coil resistance and reactance.
- The effect that the different conductor size may have on coil size (axial length) and hence its ability to withstand short circuits.