Noise In Electrical Machines Research Articles

Analysis of Skewing Effects on Radial Force for Different Topologies of Switched Reluctance Machines: 6/4 SRM, 8/6 SRM, and 12/8 SRM

Reducing vibration and noise in electrical machines for a given application is not an easy task, especially when the application imposes some restrictions. There are many techniques for reducing vibration based on design or on control. Switched reluctance motors (SRMs) have a double-saliency structure, which results in a radial pulsation force. Consequently, they cause vibration and acoustic noise. This paper investigates the correlation between the radial force and the skew angle of the stator and/or rotor circuits. The analysis is computed from two-dimensional (2D) transient magnetic finite-element analysis (FEA) of three machine topologies, namely the 12/8 three-phase SRM, the 6/4 three-phase SRM and the 8/6 four-phase SRM. Compared to SRM, these topologies have the same basic dimensions (stator outer diameter, rotor outer diameter, and length) and operate in the same magnetic circuit saturation. The flux linkage and torque characteristics of the different motors are presented. The radial force distributed on the stator yoke under various skewing angles is studied extensively by FEA for the three machines. It is also demonstrated the effect of skewing angles in the reduction of radial force without any reduction in torque production.

Comparison of Main Magnetic Force Computation Methods for Noise and Vibration Assessment in Electrical Machines

This paper presents a comparison of several methods to compute the magnetic forces experienced by the stator teeth of electrical machines. In particular, the comparison focuses on the virtual work principle (VWP)-based nodal forces and the Maxwell tensor (MT) applied on different surfaces. The VWP is set as the reference. The magnetic field is computed either with finite element analysis or with the semi-analytical subdomain method (SDM). First, the magnetic saturation in iron cores is neglected (linear B–H curve). Then, the saturation effect is discussed in a second part. Homogeneous media are considered and all simulations are performed in 2-D. The link between the slot’s magnetic flux and the tangential force harmonics is also highlighted. The comparison is performed on the stator of a surface-mounted permanent-magnet synchronous machine. While the different methods disagree on the local distribution of the magnetic forces at the stator surface, they give similar results concerning the integrated forces per tooth, referred as lumped forces. This conclusion is mitigated for saturated cases: the time harmonics are correctly computed with any of the presented lumped force methods but the amplitude of each harmonic is different between methods. Nonetheless, the use of the SDM remains accurate with MT in the air gap even with saturation for design and diagnostic of electromagnetic noise in electrical machines. However, for more accurate studies based on the local magnetic pressure, the VWP is strongly recommended.

FE-BE computation of electromagnetic noise of a permanent-magnetic excited synchronous ma-chine considering dynamic rotor eccentricity

Electromagnetic noise in Electrical Machines (EMs) occurs due to vibrations caused by magnetic forces acting onto rotor and stator surface. This is the dominant source for the considered permanent-magnetic excited synchronous machine in this paper. The radiated electromagnetic noise is sequentially calculated by a Finite Element (FE) and Boundary Element (BE) computation. An electromagnetic FE model is created to determine magnetic forces. Structure-borne sound and rotor dynamics are calculated using a structural dynamic FE model for the EM housing and the rotor. In order to predict resonance frequencies and amplitudes as reliable as possible, it is important to know the direction-dependent stiffness of the laminated rotor stacks and mechanical joints as well as their structural damping. Thereby, the properties of the laminated stack can be determined experimentally by a shear and dilatation test. Mechanical joint properties can be modelled by Thin-Layer Elements (TLEs) and the overall damping by the model of constant hysteretic damping. The radiated sound power is determined by a direct BE computation. The influence of dynamic rotor eccentricity on radiated sound power is examined for a run-up of the EM. All FE models are verified by data from experimental modal analysis.

Analysis of Vibration and Noise for Different Skewed Slot-Type Squirrel-Cage Induction Motors

The noise of electrical machines has drawn more attention in recent years due to their harm to people and the environment. Normal skewed slot has proven to be an effective method to reduce vibration and noise of squirrel-cage induction motor. Double skewed slot is superior to normal skewed slot on reducing vibration and noise. However, it is still difficult to meet the requirements of noise standards in some occasions. In this paper, based on double skewed slot, a new skewed slot type is proposed, which can offer a better effect on reducing vibration and noise. 2-D fast Fourier transform and 3-D finite-element method are adopted to analyze and compare the performance of the three types of skewed slots.

Magneto-structural simulation of an induction motor start-up using nodal magnetic forces in Elmer

For reduction of vibrations and noise of electrical machines, the computation of the magnetic force distributions and the ensuing deformations are needed. Here we utilize nodalforce method in open-source Finite Element software Elmer to compute the force distributions and the vibrations of an induction motor during start-up.

Impact of Eccentricity and Demagnetization Faults on Magnetic Noise Generation in Brushless Permanent Magnet DC Motors

Vibrations and noise in electrical machines are directly related to the characteristics of the radial forces on one hand, and mechanical behavior on the other [1, 4]. The characteristics of these forces depend on the air gap flux density, which is also influenced by other factors, such as stator slots and poles, saturation level, winding type, and certain faults. The aim of this work is to investigate the effect of eccentricity and demagnetization faults on electromagnetic noise generated by the external surface of Permanent Magnet Synchronous Machine [PMSM]. For this purpose, an analytical electromagnetic vibroacoustic model is developed. The results confirm the effect of eccentricity and demagnetization fault in generating some low modes radial forces.

A New Passive Methodology for Reducing the Noise in Electrical Machines: Impact of Some Parameters on the Modal Analysis

This paper presents a 3-D finite-element modal analysis to reduce the acoustical power radiated by a brushless permanent-magnet synchronous machines and avoid any resonance phenomena. The method is able to analyze the impact of some design parameters on all the resonance frequencies for reducing the total sound power and gives some guidelines to their choice. A less noisy prototype has been analyzed in simulation without any acoustic calculation and then built and validated with experimental results.

Magnetostriction Anisotropy and Rotational Magnetostriction of a Nonoriented Electrical Steel

Magnetostriction in nonoriented (NO) electrical steel is a possible source of vibration and acoustic noise in electrical machines. The anisotropy of the magnetostriction of NO steel can be far greater than that of its specific power loss which is often quoted. Also magnetostriction under rotational magnetization can be much higher than under alternating magnetization. This paper shows the relevance of magnetostrictive anisotropy to the rotational magnetostriction of a NO steel. An investigation of the effect of anisotropy in magnetostriction was carried out, followed by rotational magnetostriction measurements. A model based on an analogy of mechanical elasticity was used to describe the effect of magnetostrictive anisotropy on the rotational magnetostriction. Results show that a high value in rotational magnetostriction is mainly driven by its high magnetostriction in the transverse direction. The phenomenon is shown to be a source of asymmetrical deformation in the back iron of electrical machine cores where rotational flux predominates.

Effect of Magnetostriction Anisotropy in Nonoriented Electrical Steels on Deformation of Induction Motor Stator Cores

Magnetostriction in nonoriented (NO) electrical steels is a harmful source of vibration and acoustic noise in electrical machines. It is far more anisotropic than specific power loss, which results in more complexity in prediction of the vibration and acoustic noise. An investigation of the anisotropy in magnetostriction and mechanical elastic properties of a NO steel is presented in this paper. Measurements of deformation in the stator teeth of an induction motor model core were conducted in order to study the effect of the magnetostriction anisotropy. Strain due to Maxwell forces in the air gap was calculated and compared with the measured deformation. Measurement results indicate that anisotropic magnetostriction has a great impact on unsymmetrical deformation of the stator teeth of induction motor cores.

Asymptotic Fourier decomposition of tooth forces in terms of convolved air gap field harmonics for noise diagnosis of electrical machines

PurposeThe electromagnetic excited audible noise of electrical machines can be mostly attributed to radial forces on stator tooth‐heads. The methodology proposed in this paper uses numerical field simulation to obtain the magnetic air gap field of electrical machines and an analytical‐based post‐processing approach to reveal the relationship between air gap field harmonics and the resulting force wave.Design/methodology/approachThe simulated air gap field is sampled in space and time and a two‐dimensional Fourier transform is performed. The convolution of the Fourier transformed air gap field by itself represents a multiplication in space time domain. During the convolution process, all relevant combinations of field waves are stored and displayed using space vectors.FindingsThe effectiveness of the proposed approach is shown on an example machine. Particular examples of individual force waves demonstrate how the approach can be used for practical application in analysis of noise and vibration problems in electrical machines. The proposed method is compared to the result of a Maxwell stress tensor calculation. It shows that the deviation is small enough to justify the approach for analysis purposes.Originality/valueThe combination of analytically understood force waves and the use of numerical simulation by means of air gap field convolution has not been proposed before.

Electromagnetically excited audible noise – evaluation and optimization of electrical machines by numerical simulation

PurposeDisturbing vibrations and noise of electrical machines are gaining impact. The paper aims to focus on the necessity of estimating the electromagnetic, structure‐dynamical, and acoustic behaviour of the machine during designing and before proto‐typing.Design/methodology/approachAn adequate tool is numerical simulation applying the finite‐element method (FEM) and the boundary‐element method (BEM) allowing for the structured analysis and evaluation of audible noise also caused by manufacturing tolerances.FindingsThe simulated results show good accordance to measurement results. The methods and simulation tools allow the analysis and evaluation of every type of energy converter with respect to its electromagnetic, structure‐dynamical and acoustic behaviour.Originality/valueThe methods developed and proved can be applied to any electromagnetic device in general.

Resonant Frequencies and Vibration Behaviour of Stators of Electrical Machines as Affected by Teeth, Windings, Frame and Laminations

In connection with acquiring a quiet operation of electrical machines, accurate assessment of values of resonant frequencies and natural response of stators is essential. This paper presents a fundamental experimental study of the manner in which values of resonant frequencies, amplitudes of vibration and frequency response of stators at resonance are affected by the dynamics of teeth, windings, frame and laminations. The results presented should help design-engineers to determine resonant frequencies and natural response of stators accurately by proper incorporation of effects of teeth, windings, frame and laminations. Also, the physical interpretations of the results, given in the paper, would help in acquiring a better understanding of the vibration behaviour of stators in relation to the problem of electromagnetic acoustic noise in electrical machines.

Resonance Frequencies of Electrical Macchine Stators Having Encased Construction, Part II: Numerical Results and Experimental Verification

In connection with the reduction of noise in electrical machines, extensive investigations of te vibration behaviour ofthe main members of electrical machine are required. Detailed information about the nature of the frequency spectrum of the stator, the type of mode shapes associated with the various resonance frequencies and the effect of the frame is of much interest.

A discussion on the origin and treatment of noise in industrial environments - Noise of electrical machines

The control of noise in electrical machines may be effected by two separate and distinct methods. The first is the reduction of the noise at the source and the second the attenuation of this noise before it reaches the ears of the observer. Since noise reduction is costly, the problem is resolved into one of finding the most economic means of obtaining the required noise reduction, without interfering with the efficient functioning of the plant. It is generally considered that a good machine should run smoothly and quietly, so from the earliest days the designers and manufacturers have put a great deal of effort into producing quiet machines and more recently considerable research effort has been expended in explaining the basic phenomena.