变压器工作时，线圈中有交变电流，它产生的磁通当然是交变的。这个变化的磁通在铁芯中产生感应电流。铁芯中产生的感应电流，在垂直于磁通方向的平面内环流着，所以叫涡流。涡流损耗同样使铁芯发热。为了减小涡流损耗，变压器的铁芯用彼此绝缘的硅钢片叠成，使涡流在狭长形的回路中，通过较小的截面，以增大涡流通路上的电阻；同时，硅钢中的硅使材料的电阻率增大，也起到减小涡流的作用。
When a transformer works, there is alternating current in the coil, and the flux produced by it is of course alternating. This variable flux generates an induced current in the core. The induced current generated in the iron core circulates in a plane perpendicular to the direction of magnetic flux, so it is called eddy current. Eddy current losses also heat the core. In order to reduce the eddy current loss, the core of transformer is made up of insulated silicon steel sheets, so that the eddy current in the narrow loop can increase the resistance of the eddy current circuit through a smaller cross section. At the same time, the silicon in the silicon steel can increase the resistivity of the material and also play a role in reducing the eddy current.