Wednesday, January 6, 2016
Usually laminations are provided to reduce the eddy current losses taking place in the magnetic materials used to provide path for the flux. Whenever the flux linkages with the magnetic materials changes, e.m.f will be induced in the armature conductors. Apart from this, some e.m.f will also be induced in yoke and core of the machine. As there are closed paths in the yoke and core because of the induced e.m.f’s circulating current flow in them. These circulating currents are called eddy currents and the resultant I²R losses are called eddy current losses.
Both the armature core and yoke are magnetic materials used to provide path for the flux and eddy current losses taking place in both of them. But, eddy current losses in yoke are comparatively less because the induced e.m.f’s in the yoke are comparatively less. because of less variations in the flux linkages with respect to time when compared to armature core i.e., dφ/dt is less in case of stator. Hence, the stator [yoke] is not laminated whereas the armature core is laminated.