The coil has alternating current while transformer works that create alternating magnetic flow. There is constantly changing flux in iron core which create induced current that perpendicular to flux direction circulation. So we named eddy. The eddy loss also make iron core heat. The iron core could decrease another iron loss that named eddy loss.
The iron core is usually made of silicon steel sheet that is steel content of silicon which is up to 0.8-4.8%. the silicon steel is a strong magnetic conductivity that create major magnetic induction intensity in the electric coil. The transformer always work under alternating condition. The power loss is not only in coil resistance but also exist in iron core magnetized by alternating current. The power loss we usually called iron loss which caused by 2 reasons “hysteresis loss” and “eddy current loss”.
The hysteresis loss in the magnetization process exist iron loss in magnetic hysteresis. This loss is proportional to the area enclosed by the hysteresis loop of the material. The hysteresis loss of the core of silicon steel is small because of its narrow hysteresis loop.
The iron core reduces another type of iron core loss – “eddy current loss”. When a transformer works, there is an alternating current in the coil which produces an alternating flux of course. This changing flux creates an induced current in the core. The induced current in the core circulates in a plane perpendicular to the direction of flux that called eddy current. Eddy current loss also heats the core. In order to reduce eddy current loss, the core of the transformer is made of silicon steel pieces insulated from each other, so that the eddy current passes through a small section in a narrow and long circuit to increase the resistance in the eddy current path. Meanwhile, the silicon in the silicon steel increases the resistivity of the material and also reduces the eddy current.