Applications Energy Transmission
Energy Transmission
Transformer winding wire: copper and Aluminium for the grid
Distribution transformers are the quiet workhorses of the power system. They are expected to run for thirty or forty years without attention, and the wire inside them has to be chosen for exactly that. Here is how we look at it.
Heavy gauge and long life
Transformer windings use the thickest wire we make, from SWG 8 to about SWG 24 for distribution units, and larger rectangular sections for the big ones. The coil is immersed in oil at up to 105 °C for its whole life, so the covering has to be oil compatible, adhesive enough to survive the forming of the coil, and thick enough to hold off the inter-turn voltage under lightning impulse.
Polyester Grade 2 is the traditional choice for oil-filled units; polyesterimide Grade 2 or 3 for dry-type and cast-resin transformers, where the coil runs hotter and the enamel is the only insulation.
Copper or Aluminium
Aluminium has become the default for the low-voltage winding of pole- and pad-mounted distribution transformers, on price and weight. The winding is larger, but a distribution transformer has room, and Aluminium's lower density means the whole unit can be lighter even with the bigger coil. Copper stays on the high-voltage winding and on any unit where footprint or losses are constrained.
We enamel both on the same lines with the same covering grades, so a transformer shop can run copper HV and Aluminium LV from one supplier. Our Aluminium is 99.99% EC-grade; our copper is 99.99% ETP from certified cathode.
Losses, resistance and the certificates that prove them
Load loss is copper loss, and copper loss is resistance. A conductor that is undersize by one per cent raises the loss by about two per cent, and on a utility contract with loss capitalisation that is real money. We hold conductor diameter to the tight side of tolerance and measure the DC resistance of every batch, because a transformer builder cannot fix it after the coil is wound.
Each spool ships with a batch certificate listing resistance, elongation, breakdown voltage and covering thickness. Our copper carries mill certificates back to the cathode. For utilities that audit their supply chain, the file is complete before the transformer is.
Reactors, switchgear and earthing
Beyond transformers, the same heavy gauge wire winds shunt reactors and current-limiting reactors, and the bare copper we draw is used for earthing grids, switchgear connections and busbar tails. Bare wire is supplied hard-drawn for mechanical strength or annealed for bending, in coils and on reels, cadmium-free.
Key takeaways
- Oil-filled: polyester Grade 2. Dry-type and cast-resin: polyesterimide Grade 2 or 3.
- Aluminium LV plus copper HV from one supplier keeps documentation and quality in one place.
- Resistance is loss; ask for batch DC resistance and mill certificates with every delivery.
