How electrical transformers are made

Two coils share one iron core, and the ratio of their turns sets the voltage.

stations: 6
things upstream: 31
raw sources: 14
steps from the ground: 6

The short version

A transformer is two or more wire coils wound around a shared magnetic core. That core is a stack of thin steel plates insulated from each other, which cuts energy lost to eddy currents. Copper wire forms the coils, which are insulated. Larger units are dried and filled with oil.

Cut the core plates

Thin plates of silicon steel are cut to shape. Good-quality silicon steel in the core lowers energy losses.

Goes in
Sheet steel
Stack the laminated core

Plates are stacked and insulated from each other. Stacked laminations cut eddy currents compared with a solid block.
Wind the coils

Copper wire is wound on forms. The primary and secondary windings must have the number of turns that sets the voltage ratio.

Goes in
Copper wire
Insulate and fit the coils

Insulation is wrapped around the windings, and the coils are slipped over the core legs.
Dry and seal the unit

The assembly is dried to remove moisture, then encased or placed in a tank.

Goes in
Steel
Test the ratio

Voltage ratio, losses and insulation are measured before shipment.

End of the lineElectrical transformer Next it goes into microwave oven, phone charger.

Worth repeating

Faraday's law of induction, discovered in 1831, explains why a changing current in one coil induces a voltage in another.
Transformers move energy between circuits with no metal connection between them.
Better silicon steel or amorphous steel cores lower losses but raise the initial cost.