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All online materials I have read so far state that laminations reduce eddy currents but how is this so? I mean why would currents be smaller this way than having a big block of unlaminated iron core which would cause the resistance of said block to be much higher than to have it laminated? In any case even if the loops have individual smaller currents, were you to add them all up, wouldn't the sum of the currents equal that to a big eddy current flowing through the whole transformer.

Also by adding varnish or paper between the laminated layers, wouldn't this increase the reluctance of the core for the magnetic flux passing through it, increasing transformer core losses?

P.D. As side question, I know magnetic hysteresis is caused by the friction between the magnetic flux and the core molecules as they become magnetised. Therefore, does the core's reluctance value represent this fenomenon or does it just represent the inherent "magnetic resistance" characteristic to the material (and/or shape)?

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The eddy currents are electrical currents that circulate in the transformer core, making it hot and wasting power. A big solid iron core will have a very low electrical resistance, and eddy currents will have little to prevent them from circulating.

Replace the solid iron with thin sheets, with the thinnest of insulation between, and the currents can't circulate in the same way. Only to a much lesser extent in each sheet of iron.

The transformer may be slightly less efficient magnetically, but elimination of the eddy currents makes a big improvement.

For high frequency transformers, they go further and make the cores out of ferrite. That's a ceramic material with iron oxide in it.

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  • \$\begingroup\$ The sheets are perpendicular to the plane in which the eddy currents would circulate. \$\endgroup\$
    – John Doty
    Nov 29, 2023 at 17:36
  • \$\begingroup\$ Ferrite and powdered iron are different things. Ferrite doesn't have iron particles. \$\endgroup\$
    – John Doty
    Nov 29, 2023 at 17:38
  • \$\begingroup\$ I always thought ferrite contained iron, or iron oxide, of some sort (particles, powders). It's the iron that gives the ferrite its magnetic properties. This is from Wikipedia: " ferrite is a ceramic material made by mixing and firing iron(III) oxide (Fe2O3, rust) with one or more additional metallic elements, such as strontium, barium, manganese, nickel, and zinc". The description in Britannica is similar. \$\endgroup\$
    – SteveSh
    Nov 29, 2023 at 20:29
  • \$\begingroup\$ Yes, ferrite is a systematically named compound; just as sodium sulfate (Na2SO4) and sodium sulfite (Na2SO3) are named, so too there is a potassium ferrate K2FeO4 (and no, it kind of doesn't like to exist, this is a fairly rare oxidation state for iron), and zinc manganese ferrite (Zn,Mn)Fe2O4 (in this much more comfortable Fe(III) state). Which can be thought of as magnetite, ferrous ferrite (FeFe2O4), with Fe(II) substituted with Zn and Mn which have similar ionic size and charge. This has been your daily chemistry diversion :) \$\endgroup\$ Nov 29, 2023 at 20:52

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