Siegfried Rainer

Weak Coupling Between Electromagnetic and Structural Models for Electrical Machines

A weak coupling technique for an electromagnetic and a structural dynamic model formulated by the finite element method (FEM) is presented. The algorithm is able to estimate higher force harmonics with high accuracy and is hence suitable for acoustic simulations of electrical machines. High computational efforts using conventional algorithms are reduced significantly and accuracy is even enhanced. The algorithm is applied to compute vibrations of a skewed induction machine.

Validation of a Comprehensive Analytic Noise Computation Method for Induction Machines

The validation of an analytical approach to determine the noise behavior of induction machines is presented. Analytical electromagnetic, structural, and acoustical computations are performed. Data obtained by numerical computations as well as by vibration and noise measurements are compared with the analytical results.

Computation of Rotating Force Waves in Skewed Induction Machines Using Multi-Slice Models

Investigations of the noise behavior of induction machines demand the calculation of the rotating force waves and thus the determination of the field-harmonics. The goal of this paper is to develop a method to compute the field-harmonics of a skewed induction machine using a multi-slice model.

Calculation of load-dependent equivalent circuit parameters of squirrel cage induction motors using time-harmonic FEM

Two methods to determine the equivalent circuit parameters of squirrel cage induction motors (IM) are presented and compared. The first one is based on the time-harmonic finite element method (FEM) simulation of the measurement process (short-circuit and no-load test), yielding an equivalent circuit with constant parameters. In addition, the time-harmonic FEM is applied in the second method to calculate the load-dependent equivalent circuit parameters of squirrel cage IMs. Here, the material properties in a two-dimensional finite element model of the induction machine are linearized in each operating point and the superposition principle for the magnetic flux is applied to define the leakage inductances. Hence, the parameters are calculated for every operating point separately, thus the variations of the parameters due to skin effect in the rotor bars and due to material saturation under arbitrary load condition and rotor speed can be taken into account.

3-D Finite Element Analysis of Additional Eddy Current Losses in Induction Motors

In this paper, an approach based on the three-dimensional finite element analysis is proposed to evaluate additional eddy current losses in induction motors of several MW. Losses produced by induced eddy currents in the end-region of the machine (stator clamping-plates and clamping-fingers) and losses provoked by parasitic leakage fields in the housing and in the metal parts of the cooling-ducts are investigated. Furthermore, excess rotor copper losses produced by higher harmonic fields in the rotor squirrel cage are taken into consideration as well. Comprehensive three-dimensional finite element models have been prepared in order to take these effects precisely into account. A numerical procedure based on nonconforming finite element meshes has been used in order to simplify the modeling procedure and the solving process has been carried out in the frequency domain with the aim of reducing the computational time.

Determination of the starting and operational characteristics of a large squirrel cage induction motor using harmonic and transient FEM

The harmonic and transient finite element method (FEM) are used to determine the starting and operational characteristics of a large induction motor (IM). The starting properties of the initially proposed motor are strongly degraded by parasitic asynchronous crawling tendencies and the motor is unable to achieve the nominal rotor velocity. It is shown in this paper that, when analyzing the IM using the time-harmonic procedure only, these parasitic effects are not detectible. In order to enable the detection of all the effects provoked by higher harmonics the designing process has been expanded by the use of a transient numerical analysis coupled to the equations of motion. The acceleration torque, position and rotational speed of the rotor are recalculated at every time step. This way, the estimation of the newly proposed motors design is realizable, based on the simulation results only. The numerical results are compared with measurements.

Numerical and experimental investigation of the structural characteristics of stator core stacks

Purpose – The purpose of this paper is to analyse the eigenforms and eigenfrequencies of stator core stack by experimental and numerical investigation. The influence of material parameters on the structural vibrations is carried out in order to describe the laminated structure of stator core stack with a homogeneous material model. Design/methodology/approach – The finite element method is applied for a numerical modal analysis. Therefore, a homogeneous transversally isotropic material model is introduced and the influence of each material parameter on the dynamical behavior is investigated. These material parameters are stepwise adjusted to the results from the experimental modal analysis. The investigation includes results from different stator core stacks. Findings – The influence of material on the modal parameters is shown. Furthermore, material parameters are carried out for stator core stacks, which describe the measured dynamical behaviour. Originality/value – The presented investigations show a u...

Numerical analysis of steady-state operation of three-phase induction machines by an approximate frequency domain technique1

ZusammenfassungEine Vorabschätzung im Frequenzbereich wird angewandt, um die notwendigen Startwerte für die transiente Analyse im Zeitschrittverfahren zu ermitteln. Die transiente Analyse erlaubt es, zeitlich veränderliche Vorgänge, wie induzierte Spannungen, Wirbelströme und Oberwellenmomente, zu erfassen. Mit den Startwerten aus der Frequenzbereichs-Analyse kann der stationäre Betriebszustand deutlich schneller erreicht werden als bei der Annahme aller Startwerte mit null. Die Anwendung der Methode wird an?einem Strom- und Spannungs-gespeisten 2-D-Asynchronmaschinen-Modell sowie an einem 2-D-Mehr-Schichten-Modell eines Käfigläufers gezeigt.SummaryAn approximate frequency domain technique is applied to determine the initial values for the transient time-stepping numerical scheme required to take time dependent phenomena like induced voltages, eddy currents and slot ripples in induction machines into account. Using the initial conditions obtained, the steady-state operation of the motor is obtained much faster than by assuming zero initial values. This procedure is employed to the current-fed and voltage-fed 2-D induction motor models and, additionally, to the 2-D multi-slice FEM model of the 1 MW squirrel cage induction motor.

Computation of the Noise Radiation of an Induction Machine Using 3D FEM/BEM

Purpose – The purpose of this paper is to set up a comprehensive numerical approach to estimate the 3D structural vibration and noise radiation of an induction machine.Design/methodology/approach – The rotating force waves, acting in the air gap of an induction machine and obtained by an electromagnetic finite element multi‐slice simulation, are applied to the 3D structural finite element model and a structural harmonic simulation is performed. The sound emission due to the vibration of the surface of the machine is computed with a 3D boundary element model.Findings – The paper outlays problematic issues when setting up the numerical models, i.e. the structural finite element model. The material properties strongly affect the structural behaviour and therefore the radiated noise.Originality/value – The 3D force distribution in the air gap and the resulting vibrations are computed. The structural behaviour, i.e. the different vibrational behaviour of stator and surface is discussed. The correlation of the ...

Direct steady-state computation of mechanical vibrations in electrical machines

A method for steady-state calculation of mechanical or structural systems formulated by the finite element method (FEM) is presented. The procedure introduced is used to calculate the mechanical vibrations caused by the electromagnetic excitation of induction motors. Compared to other approaches, this method enables the free choice of the time discretisation algorithm. The method is presented for second order systems and demonstrated by a numerical example.