Anouar Belahcen

Interdependence of Hysteresis and Eddy-Current Losses in Laminated Magnetic Cores of Electrical Machines

This paper investigates the interdependence of hysteresis and eddy-current losses in magnetic cores. Based on the results of a numerical model developed for the analysis, the magnetodynamic loss phenomena are found to be distinctly interdependent. Because of the effects of eddy currents on the flux distribution in the lamination depth, hysteresis and excess losses show a dependence on eddy currents, and hence, on the excitation frequency. Eddy-current and excess losses, on the other hand, are affected by the magnetic characteristics of the material where hysteresis plays the role of a damper. An application of the model to a rotating electrical machine has showed that the interdependence between the losses is quite significant.

Comprehensive Dynamic Loss Model of Electrical Steel Applied to FE Simulation of Electrical Machines

This paper presents a dynamic loss model of electrical steel that can be used with the transient finite-element simulation of electrical machines. The model is used to compute the iron losses in a 37-kW induction machine fed from a sinusoidal and frequency converter voltage supply at different frequencies and loads. The computed losses are compared with results from conventional iron loss computation method based on harmonic analysis as well as with measured losses. The presented dynamic model is based on the investigation of different measurement results as well as on phenomenological backgrounds and analogies. The model is tuned to account for the rotational losses and thus can be used with arbitrary wave form or loci of the magnetic flux density vector (as is the case in the iron core of electrical machines). The parameters of the model are identified from measurements and can be stress dependent to account for the effect of mechanical stresses on the losses in magnetic materials. The presented model differs from previously presented ones in a way that the losses can be calculated at any time and not as an average over a period of the magnetic flux density.

Locally Convergent Fixed-Point Method for Solving Time-Stepping Nonlinear Field Problems

Because of its stable solution and despite its slow convergence, the fixed-point technique is commonly used for solving hysteretic field problems. In this paper, we propose a new method for accelerating the convergence of the fixed-point technique in solving time-stepping nonlinear field problems. The method ensures locally convergent iteration in an interval that contains the initial value and the fixed-point solution. We provide a thorough discussion and geometric interpretation to clarify and highlight the principle of the method. We also use a finite-element formulation to test the method by computing the magnetic field of an electric machine. Finally, we assess the efficiency and applicability of the method by a comparative investigation. The method proves to be simple and remarkably fast.

A Fast Fixed-Point Method for Solving Magnetic Field Problems in Media of Hysteresis

The paper proposes a new fixed-point method for solving time-stepping hysteretic field problems. The method is aimed to speed up the convergence of the fixed-point solution and enhance the applicability of the fixed-point iteration. The method makes use of the differential reluctivity and produces a locally convergent solution. A 1-D finite-element procedure is performed to test the method by computing the magnetic field in a ferromagnetic laminated steel. The efficiency, stability, and applicability of the method are assessed in which the method is proven simple and remarkably fast.

Locally coupled magneto‐mechanical model of electrical steel

Purpose – The purpose of this paper is to find out how to model the effect of mechanical stresses on the magnetic properties of electrical steel used in electromagnetic devices and especially in electrical machines. Further, the effect of these stresses on the operation of the machines should be studied.Design/methodology/approach – The constitutive equation of the electrical steel is usually modeled as a non linear relation between the magnetic flux density and the magnetic field strength. In this research, this constitutive equation is developed to account for the mechanical stresses through a parametric relationship, the parameters of which are estimated from measurements. Further, the constitutive equation is used in a magnetomechanically coupled numerical simulation of an induction machine.Findings – The mechanical stresses degrade the properties of the electrical steel and increase the magnetization current in electrical machines. This leads to a decrease in the efficiency of these machines.Research...

Signatures of Electromechanical Faults in Stress Distribution and Vibration of Induction Motors

This paper develops a method for determining the signatures of electromechanical faults in the airgap stress distribution and stator vibration of induction machines. Two types of induction motors are analyzed; a 2-pole pairs, star connected and an 1-pole pair, delta connected motor. The radial electromagnetic stress distribution along the airgap is calculated and developed into double Fourier series in space and time. The computations show the existence of low frequency and low order stress distributions acting on the stator of the electrical machine when it is working under faulty conditions. These stress waves are able to produce forced vibration in the stator surface. The simulation results are corroborated by vibration measurements. Modal testing is also carried out to determine the natural frequencies. The measurements and simulations show that low frequency components of the vibrations can be used as identifiable signatures for condition monitoring of induction motors. The patterns presented by the faults allow to discriminate between them.

Losses in an eccentric rotor induction machine fed from frequency converter

The rotor eccentricity in induction machines has been studied from different points of view as to assess its possible detection. However, most of the inductions machines in industry are allowed to operate under different levels of eccentricity. In this paper we investigate the effect of rotor eccentricity (both static and dynamic) on the power losses of the machine when fed from PWM voltage sources. Already at 30% static eccentricity the rotor resistive loss increased by more than 7%. This increase is crucial for the cooling of the machine. It is also shown that for the same level of eccentricity the static one causes slightly more losses than the dynamic one. Analysis of the torque, phase voltages and currents under static and dynamic eccentricity is also presented.

Local Magneto-Mechanical Coupling in Electrical Machines

Original results of numerical simulations of an induction machine with local magneto-mechanically coupled FE model are presented. The coupling is implemented locally as a stress dependency of the magnetization properties of lamination. The mechanical load is due to the magnetic forces and shrink fitting of the core into the frame. Large local stresses are caused. They reduce the magnetization of lamination and increase the stator current. The resistive power losses increase and add to increased iron losses due to stresses. The efficiency of the machine is reduced

Magnetoelastic coupling and Rayleigh damping

This paper presents a magnetoelastic dynamic FE model. As first approach, the effect of magnetostriction and strong coupling is not considered. The effect of Rayleigh damping factors on the vibrational behaviour of the stator core of a synchronous generator is studied using the presented model. It shows that the static approach is not accurate enough and the difference between calculations with damped and undamped cases is too important to be ignored. However, the difference between damped cases with reasonable damping is not very important.