In electric machines, a varying magnetic field causes eddy currents in all metallic parts and hysteresis in ferromagnetic core. The losses caused due to eddy currents are known as eddy current loss and that caused due to hysteresis is known as hysteresis loss.

What causes eddy current?

Eddy currents are currents which circulate in conductors like swirling eddies in a stream. They are induced by changing magnetic fields and flow in closed loops, perpendicular to the plane of the magnetic field. ... Like any current flowing through a conductor, an eddy current will produce its own magnetic field.

Why do eddy current losses occur?

Eddy current losses are the result of Farady's law, which states that, “Any change in the environment of a coil of wire will cause a voltage to be induced in the coil, regardless of how the magnetic change is produced.” Thus, when a motor core is rotated in a magnetic field, a voltage, or EMF, is induced in the coils.