Slot fringing effect on the magnetic characteristics of the electrical machines

Due to the fringing effect, magnetic flux in the air gap of electrical machines is reduced. This leads to enlarged effective air gap length. Currently, the Carter coefficient is applied to compensate the slot effects. This coefficient is calculated with respect to the slot 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 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.