Slot fringing effect on the magnetic characteristics of the electrical machines

Due to the fringing effect, the magnetic flux in the air gap of electrical machines is reduced. This leads to the larger effective air gap length. For this reason, in the design stage of the electrical machines, a larger magnetic flux must be chosen. On the other hand, magnetic loading must be taken smaller than the value corresponding to the real air gap length. Currently, Carter coefficient is applied to compensate the slots effects. This coefficient is calculated with respect to the slots dimensions and air gap length, using Carter formulas and corresponding curves. These curves are taken by solving the two dimensional Laplace equation for voltage, and cannot be accurate (errorless) completely. Nowadays, using the FEM (finite element method) packages of numerical methods, slot effects on the air gap flux distribution are calculated carefully. In this paper using the Ansys package of FE these effects are studied. Using the results of these studies and comparing them with the Carter method, the Carter coefficient is modified.