Why thetransformercoreis laminated?

A transformer core is laminated to reduce eddy currents, which are small currents caused by the changing magnetic field of the alternating current in the first coil. Eddy currents can disrupt the flow of electricity from the primary coil to the secondary coil, and they can also cause energy loss by converting kinetic energy to thermal energy.

Laminating the core with thin iron sheets that are coated with an insulating layer and glued together creates small gaps between the laminations:

Eddy currents

The insulating layers act as a barrier to eddy currents, forcing them to flow in narrow loops within the thickness of each lamination. The gaps between the laminations also increase the coil's resistance, which decreases the total current and eddy current losses.

Overheating

The densely packed laminated sheets reduce circulating currents in the core, which lowers the transformer's energy loss and reduces overheating.

Efficiency

Removing air gaps between the laminations can increase efficiency, while larger gaps can lead to higher losses and lower efficiency.