Most transformers have cores made of thin laminations of silicon steel. As the steel core is also conductive, it has currents induced in it by the changing magnetic flux. Insulating the layers from one another helps to reduce eddy currents, and the insulation is used to prevent the laminations acting as a solid piece of steel. The thinner the laminations, the lower the eddy currents and the lower the losses, however very thin laminations are usually expensive. Most transformers use the traditional ‘E’ and ‘I’ shaped laminations, stacked alternately in order to reduce any air gap; however there are other types such as ‘C’ cores
‘C’ cores are made by winding silicon steel strips around a rectangular form. Once the required thickness has been achieved, it is removed and the laminations bonded together. It is then cut in half to form two ‘C’ cores. The faces are then smoothed to ensure that they fit together with the smallest possible gap, in order to reduce losses. The coil is placed over one half of the core, which is then assembled and tightly held together by a steel strap.