Electrical Steel Laminations Research Articles

Coating induced residual stress in nonoriented electrical steel laminations

Abstract

Influence of Punching and Tool Wear on the Magnetic Properties of Nonoriented Electrical Steel

Because electric cars are manufactured in high quantities, the influence of punching of nonoriented electrical steel with respect to tool wear becomes an important topic for the automotive industry. With regard to quality assurance, it is necessary to investigate the local degradation of the magnetic properties due to the plastic deformation caused by the cutting process. In this contribution, both the local changes of the microstructure of the material and the magnetic properties will be considered. Different methods for analyzing the manufactured electrical steel laminations were applied. Cutting edges generated under different states of tool wear were examined by means of optical microscopy and electron backscatter diffraction to visualize the influence of plastic deformations. The magnetic properties of punched electrical steel laminations as a function of increasing tool wear have been determined by hysteresis measurements of stacked ring cores. With respect to quality assurance purposes spatially resolved measurements have been carried out to determine local magnetic properties and find a suitable correlation to application-relevant quantities.

A Specific Magnetic Losses Calculation in Non Oriented Electrical Steel Laminations

The paper intends to study the magnetic losses of non-oriented electrical steel laminations under sinusoidal voltage supply. The measurement of magnetic losses of electrical steel laminations in Epstein Frame is implemented step by step at frequency range from 50 Hz. The calculation of the magnetic losses is made by using two methods based on the statistical loss model. Our contribution consists on the first model which corresponds to the curve fitting method which needs many experimental data but allows a better exactitude. The second method is defined in a time domain, in order to account of the presence of harmonics in the flux density wave form. The coefficients of the second method are determined from the curve fitting. A good agreement between practice and theory was established with these two methods

Opportunities and Precautions in Measurement of Power Loss in Electrical Steel Laminations Using the Initial Rate of Rise of Temperature Method

A system has been developed for measuring localized power loss of electrical steel laminations based on the initial rate of rise of temperature method. Hardware and software components were designed and developed individually to make an accurate measuring system. Three experiments were carried out to calibrate the system and quantify its accuracy over a wide measurement range. The application of the measuring system was demonstrated in two cases of measuring localized power losses near bolt holes in laminations and near artificial lamination edge burrs in a 300 kVA, 3 phase transformer core. The experimental results show that the developed system can measure localized power loss over a wide range with uncertainty of measurement less than ± 2%, but precautions are necessary when interpreting measurements in regions where the magnitude of the loss varies significantly over distances of less than a few centimeters.

Application of Taguchi Method for the Optimum Design of a 3MW Permanent Magnet Synchronous Generator

The paper is examined to establish the optimal set of control parameters for the design of a 3MW direct-drive permanent magnet synchronous generator by applying the Taguchi method. Taguchi orthogonal array is employed to determine the optimal combination of design parameters, including: steel lamination material, applied voltage, slot number, diameter of air-gap, magnet pole materials, magnet pole depth, stator outer/inner diameter, and length of stator core under the rated rotating speeds of the generator. Next, core loss database of used electrical steel laminations in generator was investigated. Effect of these control parameters of the permanent-magnet synchronous generator on the output power and efficiency are also analyzed in the paper. Results show that the designed 3MW direct-drive permanent magnet synchronous generator is capable of operating stably and assure the adequate 3MW power output and good efficiency greater than 95%.

Rotational Core Loss and Permeability Measurements in Machine Laminations with Reference to Permeability Asymmetry

Rotational core loss and vector magnetization in electrical steel laminations are investigated under the circular 2D rotating field. The loss under a rotating field is compared with the loss under a pulsating field, and the behavior of the dynamic hysteresis loops in both cases are explained with reference to permeability asymmetry. The permeability of the magnetic material under the rotating field tends to change based on the flux direction. Experimental data is obtained using a new test fixture based on an electromagnetic Halbach array, which is capable of measuring rotational and pulsating losses in circular steel laminations. The measurements were performed for M15 gauge 29 electrical steel material at three typical frequencies of industrial interest (60 Hz, 400 Hz, and 1 kHz), and results are presented and discussed. It is found that there is a relation between the direction of applied field and the permeability, in addition to a strong effect on the permeability in the case of rotational flux when compared to pulsating flux.

Effect of Artificial Burrs on Local Power Loss in a Three-Phase Transformer Core

The increase in losses due to burrs occurring on cut edges of electrical steel laminations in transformer cores is difficult to quantify. Artificial burrs were applied to a 350 kVA, three-phase, five packet, transformer core. Total core loss, flux density distribution and local loss near the burrs were measured. Burrs applied to a portion of a packet of laminations in one limb caused the flux distribution to become more nonuniform than normal throughout the whole core. Local losses increased significantly outside the burr region. The loss increased to over 1000 W/kg in the severely burred region at 1.8 T, 50 Hz. Measured flux distribution data was used in simplified eddy current calculations to predict the total and localized losses. The predicted and measured localised losses in the burred regions followed similar trends but did not agree well in magnitude probably due to the errors caused by the simplifications and assumptions which were necessary in the eddy current analysis.

Building Factor of Grain-Oriented Silicon Iron (3% SiFe) with Different Thickness on 100kVA Three Phase Distribution Transformer Core

The power loss in laminated transformer cores is always greater than the nominal loss of the electrical steel laminations, by a factor known as the building factor. This paper discussed result of an investigation towards the effect of using two different Grain-Oriented Silicon Iron (3%SiFe) materials to the 100kVA three phase distribution transformer. The thicknesses of the material that have been used in this research are 0.23mm and 0.27mm. The transformer core will be assembled with 60o T-joint with 5mm mitred corner overlap length. Power loss has been measured using no-load test with 29 layer of lamination while nominal loss measured using Epstein test frame. At the operation mode flux density, 1.5T, the building factor of the transformer model core material with 0.23mm thickness is 1.219 while with the building factor for 0.27mm thickness is 1.250. This shows that thinner transformer core lamination is better than the other one by 2.5% during operation mode.

Measurement and Modeling of 2-D Magnetostriction of Nonoriented Electrical Steel

Magnetostriction of nonoriented electrical steel was measured under rotating flux magnetization conditions which occur in AC electrical machine stator cores, and compared with the magnetostriction calculated from a model based on a mechanical elasticity analogy. Shear magnetostriction and magnetostriction perpendicular to the magnetization direction are accounted for in the model which leads to an accurate representation of magnetostriction throughout the electrical steel lamination plane. This has the potential for improving the accuracy of stator core deformation and vibration calculations.

Estimation of Core Losses on Electrical Steel Laminations in Wind Generators Using Epstein Frame and Expanded GSE Method

The paper intends to study the core losses of non-oriented electrical steel laminations under high frequency voltage excitations. The measurement of core losses of the electrical steel laminations in Epstein Frame is implemented step by step from 50 Hz to 5000Hz. The accuracy of results evaluated from Expanded GSE method is compared with those tested by Epstein Frame. The core loss database for three different kinds of medium, medium-high and high quality electrical steel laminations (50CS350, 50CS470, 50CS600) is completed in the paper. Also, 85 test points of core loss data are established in the flux density ranging from 0.3T to 1.8T and in the power supply frequency ranging from 50Hz to 5000Hz. Maximum core loss value is close to 443W/kg. The tested core loss data and the Expanded GSE models are useful and may cover for the applications of large-scale wind-driven generators and general motors. They also enough provide designers with the accurate information to minimize the core losses of wind turbine generators.

Effects of Core Materials and Operating Parameters on Core Losses in a Brushless DC Motor

The development of high-efficiency DC motors is a very important technique subject from the viewpoint of energy saving. In order to increase the motor efficiency, three different grades of electrical steel laminations are used to design a brushless DC (BLDC) motor in the paper since they provide reduced core losses. A measurement of core losses of three different grades of electrical steel laminations in Epstein Frame is implemented to determine the WT-Bmax core loss curves under sinusoidal waveform step by step from 60 Hz to 5000Hz. The core losses in a BLDC motor fed by a PWM control DC Square-Wave voltage supply are estimated using the WT-Bmax core loss curves. The effects of three core materials on the core losses of the BLDC motor have been studied in the paper. The computed core losses are compared to those evaluated by using a 2D finite element analysis. The effects of various operating conditions on the core losses in the BLDC motor laminations are also investigated in this paper. The presented results give guidelines to the selection of core materials and the operating points to improve motor efficiency.

Effect of Artificial Burrs on the Total Power Loss of a Three-Phase Transformer Core

Burrs occurring on electrical steel laminations are likely to increase the losses of transformer cores; however, it is still difficult to quantify this effect. Artificial burrs were applied to a three-phase distribution transformer core in a controlled manner. When large burrs, short circuiting 66 laminations together, were applied to the core, total loss at 1.8 T rose by almost 100%. From eddy current analysis, localized losses were estimated to increase to 1500 W/kg at 1.8 T for 66 laminations electrically connected by burrs. Additionally, various burr locations were investigated and it was found that it does not matter whether the burrs placed on one limb are located opposite each other, forming a rectangular affected region, or are shifted, forming a skewed shape. For burrs affecting a low number of laminations the calculated and measured losses agreed whereas, for large burr regions, calculated values were higher due to the approximations made.

Embrittlement of electrical steel laminations by nitrogen pick-up during heat treatment

Abstract Heat treated electrical steel laminations have shown evidence of low ductility behavior, characterized by a small number of bends till fracture, on repeated bending tests. The laminations were produced using a new grade of electrical steel with much lower aluminum content than usual. The problem happens when the oxygen potential (measured by the dew point of the atmosphere) of the heat treatment atmosphere is abnormally high. Furthermore, ductility can be restored by a low-oxygen potential heat treatment. Although the heat treatment resulted in a loss of ductility, the magnetic properties were not deteriorated. The low ductility samples always show intergranular fracture, whereas the un-treated laminations fracture by cleavage. The low ductility is associated with the formation of silicon–manganese nitride precipitates formed at grain boundaries, although they are not the cause of the low ductility. Ductility could be restored by a low dew point heat treatment but the inclusions remained in the grain boundaries. The low ductility and its recovery must be ascribed to the presence of nitrogen atoms segregated to the grain boundaries when the heat treatment atmosphere has a high oxygen potential. The lack of aluminum in the composition of the steel hinders the scavenging effect of this element on nitrogen atoms in solution in the steel.

Measurement of the stress sensitivity of magnetostriction in electrical steels under distorted waveform conditions

Electrical steel laminations used in the construction of transformer cores are subject to stresses introduced during their construction and analysis of the effect of this on the magnetostriction of the lamination has been investigated previously. It has been shown that higher harmonics of magnetostriction are of greater importance than the fundamental when considering transformer noise. Whereas previous studies have concentrated on the magnetostriction harmonics generated by sinusoidal magnetization, this investigation seeks to understand the relationship between harmonics present in the magnetization waveform and those in the magnetostriction waveform. A measurement system has been designed based on a similar principle to one previously described. In this case, a single Labview Virtual Instrument (VI) is used for the control of the applied stress, controlled magnetization and measurement of magnetostriction together with other magnetic parameters such as specific total loss, specific apparent power, permeability, coercivity and remanence. An adaptive digital feedback algorithm is utilized for control of arbitrary waveform which may be constructed from discrete harmonics or read from an input waveform. As well as measuring peak magnetostriction the software utilizes an FFT to calculate the harmonics of magnetostriction at each stress point. The effect of harmonics introduced into the magnetization waveform on the magnetostriction harmonics will be shown at various applied stresses. A harmonic, Harm B in the flux density waveform is shown to have the effect of producing a dominant harmonic in the magnetostriction given by (Harm B+1)/2.

Space Mapping Optimization of the Magnetic Circuit of Electrical Machines Including Local Material Degradation

Production processes like cutting, performed on electrical steel laminations, influence their magnetic properties locally. Since the magnetic design of electrical machines does not take this effect into account accurately, the design may be suboptimal. Therefore, the need exists to develop a numerical procedure which is capable of optimizing electrical devices, taking into account the local material degradation and featuring high accuracy and acceptable calculation time. We developed a space mapping procedure meeting these requirements and we quantified the influence of the material degradation on the design of a switched reluctance motor (SRM). The results of the optimization show that the local material degradation has a significant influence on the dimensions of stator and rotor yoke

Loss Prediction in Electrical Steel Laminations and Motor Cores

There is a growing demand to predict iron losses in laminations or in magnetic cores more accurately. Losses can be predicted in laminations under known magnetising conditions using Preisach or other methods with accuracyto within 5% of measured values being claimed. The state of magnetisation is far more complex in motor or transformer cores and empirical prediction becomes impossible due to effects of temperature, mechanical stress and other building dependent parameters. This review summarises the loss mechanisms and means of analysis before showing practical results of loss prediction using different approaches applied to single laminations or machine cores. It is demonstrated that good progress has been made over the past few years and that it is now becoming feasible to predict machine core losses with accuracy better that ′3%.

Modelling losses in electrical steel laminations

The possibility of obtaining a voltage-driven solution of the diffusion equation by using a history-dependent hysteresis model based on the transplantation principle and a model for excess loss simulation derived from the Landau–Lifshitz–Gilbert equation for magnetic viscosity is presented. The proposed solver appears to be more versatile than existing models and can predict the total losses under arbitrary magnetising conditions as well as reproduce any frequency dependence of the excess losses. The model was tested on nonoriented (NO) and grain-oriented (GO) electrical steels under sinusoidal flux density over a frequency range from 50 to 400 Hz. Initial calculations, performed without viscosity being taken into account, gave underestimated losses with reduced RMS errors which varied from 5% for NO to 10% for GO steels. By introducing viscosity, this error reduced to 1% for both materials. The model parameters are thought to be material dependent so it is reasoned that the model can be used to accurately predict losses in a wide range of materials magnetised under sinusoidal as well as nonsinusoidal flux waveforms.

Complementary finite element magnetodynamic formulations with enforced magnetic fluxes

Two complementary 3D finite element formulations, with either the magnetic field or the magnetic vector potential as unknowns, are developed to deal with the modeling of eddy currents in electrical steel laminations. The magnetic flux through the flux gates of the conducting region is imposed via the boundary terms of the weak formulations, in a natural way thanks to the use of edge finite elements. The two formulations are applied to a simple 1D eddy current problem with analytical solution. As a practical 3D application example, a T‐joint region of an electrical steel lamination is considered.

Calculation of eddy currents and associated losses in electrical steel laminations

Starting from the well known analytical formula for the eddy current losses in electrical steel laminations, saturation and edge effects are studied by means of 1D and 2D finite element models of a single lamination. A novel method for directly including the laminated core energy dissipation in a time stepped 2D model of a complete (rotating) machine is proposed. By way of example the method is applied to a tooth model with enforced flux waveforms.

Calculation of the rotational power loss in electrical steel laminations from measured H and B

An expression is derived for the calculation of the rotational power loss in electrical steel laminations, i.e., the iron loss associated with the torque caused by the angle of lag between H and B. It is shown that for a nonpurely rotating flux density, i.e., noncircular flux density loci, the instantaneous angular velocity of the flux density vector can vary substantially during a cycle, and must be accounted for in the calculation. >