What is the primary purpose of insulating the laminated sheets in transformer cores?

• A. Electrically insulate laminations to prevent current flow
• B. Improve mechanical strength
• C. Increase magnetic flux
• D. Reduce thermal resistance

Answer: (A)

The main idea is to stop eddy currents in the core by electrically isolating the laminations from one another. When the transformer’s core is subjected to an alternating magnetic field, currents are induced in the conductive metal. If the laminations were in electrical contact, those currents could circulate through large loops spanning multiple sheets, causing significant eddy-current losses and heating. By insulating each sheet, those current paths are broken, so any induced currents are confined to the thin individual lamination. The result is a drastic reduction in eddy-current losses and better efficiency, since heat from these currents is what wastes energy.

This insulation isn’t intended to provide major mechanical strength, nor does it increase the magnetic flux. Flux is determined by the magnetizing force and the core’s magnetic path, and insulation doesn’t raise permeability. It also isn’t primarily about reducing thermal resistance; the key benefit is suppressing unwanted circulating currents within the core.