Iron core Eddy current loss

Spinel ferrites, isostmctural with the mineral spinel [1302-67-6] MgAl204, combine interesting soft magnetic properties with a relatively high electrical resistivity. The latter permits low eddy current losses in a-c appHcations, and based on this feature spinel ferrites have largely replaced the iron-based core materials in the r-f range. The main representatives are MnZn-ferrites (frequencies up to about 1 MH2) and NiZn-ferrites (frequencies 1 MHz). 

Rc Resistance to account for eddy current losses in the iron core. N Turns or transformation ratio. 

Eddy current loss. The time-varying flux not only induces current in the secondary winding of the transformer but also induces circulating currents in the core as well (Fig. 2.37(a) and Fig. 2.37(b)). These eddy currents, as they are called, cause ohmic heating of the core and hence a loss of power. Power transformers normally have laminated cores made of alternate layers of iron and insulating material to coil erupt the flow of the eddy currents and thus reduce the eddy current loss (Fig. 2.37(c)). 

Loss due to energy being converted to sound in the core. This phenomenon, called magnetostriction, is of importance only in very large power transformers. The combination of the eddy current and hystersis losses is called the iron loss. 

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