The authors outline a technique which enables two-dimensional finite-element analysis to be applied to skewed machines. It involves representing the continuous skewing in a series of discrete steps. Each step may be modelled in two dimensions. The model has been applied to a salient-pole synchronous generator and to a cage induction motor. It is shown that the model is successful in removing phantom slot-ripples from the current and voltage waveforms. >

Representation of skew in time-stepped two-dimensional finite-element models of electrical machines

We present an assessment of the effect of rotational losses on an induction machine. The assessment provides an estimate of the iron losses in an induction machine by three methods, all of which rely on the output data of a two-dimensional finite-element method: 1) calculating iron losses as if they were produced by a purely alternating field; 2) calculating the iron losses by adding the losses produced by the orthogonal components of the flux density, as if the losses produced by these components were independent phenomena; 3) applying a correction factor based on experimental data to improve the rotational loss calculation. The correction factor is a function of the peak flux density value and the ratio of the major to the minor axis of the flux density loci. The third method represents the main contribution of this paper to the field and is explained in detail. Finally, a discussion of the results addresses two aspects: the location where rotational fields occur, and their impact on the total loss calculation.

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Estimating rotational iron losses in an induction machine

A means by which the finite-element method can be used in conjunction with the conventional equivalent circuit model to determine the equivalent circuit components for a three-phase cage induction motor is described. The method uses separate finite-element models for the rotor and the stator, consisting of one slot pitch and one phase band, respectively. The use of minimal models leads to a fast execution time. The method is illustrated by comparing computer predictions of performance with test measurements made on four motors, ranging in size from 4 to 150 kW.

Calculation of cage induction motor equivalent circuit parameters using finite elements

Recursive identification of induction motor parameters

Statistics show that 80% of faults are due to eccentricity in induction motors, promoting many research efforts still devoted to the eccentricity in these motors. This paper classifies different common faults in the stator and rotor. It then presents analysis techniques for faulty induction motors. Four more applied methods in the diagnosis and detection of faults in induction motors are investigated and critiqued. The finite difference method is introduced, and its drawbacks are noted. An equivalent magnetic circuit method is then discussed as a fast but less accurate method. The reduced accuracy of the latter method is due to neglect of the spatial harmonics, the relationship between these harmonics, and time harmonics, and particularly non-linearity of the magnetic materials. An analytical method of winding functions is investigated for the analysis of faulty induction motors. This method also neglects the spatial harmonics and their relationship with time harmonics, which could considerably influence ...

Different Faults and Their Diagnosis Techniques in Three-Phase Squirrel-Cage Induction Motors—A Review

The authors describe two methods for predicting the performance of cage induction motors using finite elements. The first, which is suitable for steady-state analysis, uses a phaseband model for the stator together with a single-slot model for the rotor. These are used in an iterative procedure to determine the components of the familiar per-phase equivalent circuit. The second method, which is suitable for transient analysis, uses a time-stepped coupled circuit model for the machine, together with magnetostatic finite-element field solutions which are used to update the circuit parameters. Both methods are illustrated by comparison between experimental and computed characteristics for a four-pole 4.5 kW motor. >

L.H. Lim

Papers

Finite-element models for cage induction motor analysis