What condition reduces eddy current losses in transformer cores?

What condition reduces eddy current losses in transformer cores?

• A. Low-resistivity laminated core.
• B. High-resistivity lamination with proper orientation.
• C. Non-laminated solid copper core.
• D. Insulating between windings without laminations.

Answer: (B)

Eddy current losses come from changing magnetic flux inducing circular currents inside a conductive core. These currents heat the core, and their size depends on how easily currents can flow across the cross-section. Using thin sheets of electrical steel that are insulated from each other breaks the paths that eddy currents can take. The insulation raises the resistance between sheets, so the induced currents stay confined to the thin layer within each sheet and can’t form large loops through the whole core. Pairing those insulated laminations with proper orientation of the sheets relative to the flux direction further minimizes the loop area and takes advantage of the steel’s favorable magnetic properties along the grain. So high-resistivity lamination with correct orientation is the most effective way to reduce eddy current losses. The other options don’t achieve that combination: a low-resistivity laminated core still lets sizable eddy currents flow; a solid non-laminated core (even with insulation between windings) allows large looping currents; and insulating only between windings doesn’t address eddy currents in the core itself.

Eddy current losses come from changing magnetic flux inducing circular currents inside a conductive core. These currents heat the core, and their size depends on how easily currents can flow across the cross-section.

Using thin sheets of electrical steel that are insulated from each other breaks the paths that eddy currents can take. The insulation raises the resistance between sheets, so the induced currents stay confined to the thin layer within each sheet and can’t form large loops through the whole core. Pairing those insulated laminations with proper orientation of the sheets relative to the flux direction further minimizes the loop area and takes advantage of the steel’s favorable magnetic properties along the grain. So high-resistivity lamination with correct orientation is the most effective way to reduce eddy current losses.

The other options don’t achieve that combination: a low-resistivity laminated core still lets sizable eddy currents flow; a solid non-laminated core (even with insulation between windings) allows large looping currents; and insulating only between windings doesn’t address eddy currents in the core itself.