A Vandenput

Calculation of the flux density and the unbalanced pull in two pole induction machines

ContentsIn this paper, the relationship between the homopolar flux generated by a statically eccentric rotor and the unbalanced magnetic pull in two-pole induction motors is considered. We will show that due to this kind of eccentricity, a homopolar flux is generated having the supply frequency, yielding a vibrational component of the unbalanced magnetic pull with the double supply frequency.ÜbersichtIn der vorliegenden Arbeit wird auf die Verknüpfung der Unipolarflüsse mit den Radialkräften bei 2poligen Drehstromasynchronmaschinen näher eingegangen. Es wird nachgewiesen, daß sich bei statisch exzentrischer Verlagerung des Läufers in zweipoligen Drehstromasynchronmaschinen netzfrequente Unipolarflüsse ausbilden können, die Rüttelkräfte von doppelter Netzfrequenz zur Folge haben.

Analysis of the Audible Noise of Three-Phase Squirrel-Cage Induction Motors Supplied by Inverters

One of the major problems in inverter-fed motors is the high level of audible noise produced by harmonic current and voltage components. To analyze these phenomena the field in the machine airgap is calculated using the rotating field theory together with the Maxwell stress theorem. This analysis yields a way for predicting the spectrum components produced by the motor and for relating it to the airgap flux density distribution time harmonics caused by the nonsinusoidal supply. The theoretical approach is used for calculating the airgap flux density distribution and the frequency spectrum components of a small three-phase squirrel-cage induction motor fed by a six-step voltage source inverter (VSI) and by a pulsewidth-modulated (PWM) inverter. The theoretical results are compared with experiments.

Influence of Torsional Vibrations on Lateral Oscillations of Induction Motor Rotors

The combination of torsional vibrations in induction motor drive systems and the inevitable eccentricity of the machine rotor may lead to inadmissible lateral oscillations of this rotor. In this paper we will discuss the influaence of the torsional vibrations in an analytical way and using digital simulation techniques. Special attention will be given to the frequency-content of the vibrations. The theoretical results are compared with experimentally obtained values.An adaptive power factor controllerfor three-phase inducti on generators (and also for motors) is proposed in this paper. The controller senses the reactive current drawn by the machine and accordingly provides the needed reactive power to improve the power factor to as close to unity as possible. The controller is a modular, low-cost, harmonic free device. It does not create any transients in line current. It is designed to eliminate the self-excitation problems associated with induction generators. The controller is tested on an induction generator, which is being used in wind energy and similar applications.

Microcomputer-controlled torque calculator in DC drives

The indirect method for torque measurement in DC drives is presented. The microcomputer-controlled device calculates the torque from a voltage, a current, and a speed signal, using some preliminary stored values of parameters and characteristics. To avoid the temperature dependency of the resistance, the electromotive force (instead of the terminal voltage) is indirectly measured using a so-called electromagnetic force bridge. Experimental results prove the accuracy and the convenience of this method. It is concluded that the greatest merit of the indirect method consists in the fact that no mechanical impact on the installation is necessary. >

The complete theory of cross-magnetization in uniform air-gap electrical machines

ContentsThe physical fundaments of the cross-magnetization effect necessarily having the same properties in salient pole and uniform air-gap machines is discussed. For the sake of a clear discussion, a mathematical model function of the saturation curve is applied. It is shown that under the investigated conditions, in contrast with the salient pole machines where the induced voltage originates essentially due to cross0magnetization, in uniform air-gap machines the induced voltage possesses two sources: the main field rotation (speed voltage) at the one hand, and cross-magnetization at the other. Repeating the Hallenius experiments under precisely defined conditions, the experimental proof of the theory is given.ÜbersichtDie physikalischen Grundlagen der Quermagnetisierung, die notwendigerweise gleiche Eigenschaften in Maschinen mit ausgeprägten Polen und in Maschinen mit gleichmäßigem Luftspalt haben, werden behandelt. Für die Sättigungskurve wird zwecks einer möglichst genauen Auswertung eine mathematische Modellfunktion eingesetzt. Es wird gezeigt, daß für die untersuchten Zustände, im Gegensatz zu Maschinen mit ausgeprägten Polen, wo eine induzierte Spannung praktisch nur durch Quermagnetisierung zustande kommen kann, die induzierte Spannung in Maschinen mit gleichmäßigem Luftspalt zwei vesschiedene Quellenhat: die Quermagnetisierung und das Rotieren des Hauptfeldes. Der experimentelle Beweis wird gebracht, indem das Hallenius-Experiment unter präzisen Umständen wiederholt wurde.

Electromagnetic Influence on the Radial Vibrations of Two-Pole Induction Motors

Due to the eccentric position of the rotor with respect to the stator bore, radial forces, mostly referred to as unbalanced magnetic pull (ump), are generated in the machine air-gap, influencing the radial vibration behaviour of the rotor.

CAE-Techniques for Calculating Natural Frequencies of Machine Stators

The continuous increase in the application of electrical machines these days has resulted in a growing awareness of their noise problems. Owing to economic pressures, modern design trends towards the use of less active material, which may lead to noisy electrical machines. Stricter regulations (e.g. the review of ISO-standard 1996) for noise control are now being enforced. Furthermore, electrical motors are more and more introduced in formerly silent surrounding (e.g. motors of air-conditioning installations and in personal computer systems).

The electro-mechanical torsional vibration behaviour of a.c. machines and drives

Many vibrational problems have been encountered in drive systems. The steady-state torsional vibrations of a.c. generating sets became so large that a successful parallel operation was impossible. During the starting of drive systems electrical as well as mechanical transient phenomena occur simultaneously. Under certain circumstances these transients can cause serious damage, particularly when the motor is coupled with the load through a transmission system. Sudden shaft failures from the past are some illustrative examples. From analytical and digital analysis we know that transient torques differ totally from steady-state torques, but accurate measurement of these transient torques still remains a big practical problem.