R De Weerdt

Finite element analysis of steady state behavior of squirrel cage induction motors compared with measurements

The paper describes the steady-state analysis of squirrel cage induction motors using a two-dimensional finite element solution. Saturation is included using an iterative process combining both static and time-harmonic solutions. The motor end-effects are calculated using 2D and 3D finite elements including a lumped parameter approach during the solution of the time-harmonic problem. Both motors types, with closed and open rotor slots, are analysed. Different operating points for load, no-load and locked rotor situations are analysed and compared. The influence of the different end-effect parameters is analysed by including or neglecting them in the calculations. Good agreement with measurements are found for all operating conditions. The calculations are performed using a commercial FEA package.

End ring inductance of a squirrel-cage induction motor using 2D and 3D finite element methods

The paper describes the calculation of the inductance of the end ring of a squirrel-cage induction motor using finite elements. The inductance values are obtained using 2D and 3D finite elements and the results are compared with an analytical solution. The ring inductance is split into a leakage component and a mutual component describing the coupling between end ring and end winding. The variation of both components at different load situations is described. It is shown that the ring inductance has significant influence at the locked rotor. This influence is shown by calculations of the locked rotor current with and without inclusion of the end ring inductance using a 2D finite element method. Comparisons with measurements are given.

A Combined Finite Element — Circuit Model of a Squirrel-Cage Induction Motor

The paper describes the results of a squirrel-cage induction motor analysis taking saturation and motor end effects into account. The main part of the induction motor analysis is formed by an iterative method earlier developed by Belmans et al.1 allowing the inclusion of saturation in the solution. The method can be summarised as follows: The procedure starts (for current-driven mode of operation) by solving two static non-linear problems, with real and imaginary part of the stator currents as input. From these solutions an averaged reluctivity vector is generated. This vector is used with the time-harmonic solver to obtain a first estimate of the induced rotor currents. After the time-harmonic solving, two new static problems can be defined, but now with the real and imaginary part of both stator and rotor currents as input. A more accurate reluctivity vector can be extracted. This procedure is repeated until convergence is reached. For the voltage-driven mode, the procedure starts with a time-harmonic solution generating a first estimate of both stator and rotor currents. During the time-harmonic solution, end effects of the motor are taken into account. This is done by linking the finite element model with external sources and impedances 2. The time-harmonic solver solves both the finite element model and the circuit equations from the external circuit. Temperature effects are included by a variation of the conductivity of the stator winding and the rotor conductors. Since the end-effect parameters are introduced in the model as lumped parameters, values must be assigned to them. These values are calculated from analytical formulas or using a finite-element approach.