Natheer Alatawneh

Design of a Novel Test Fixture to Measure Rotational Core Losses in Machine Laminations

The need for testing magnetic materials used in electric machine laminations and measurements under a rotating field is of importance in machine design. In order to obtain satisfactory experimental data, the design of the measurement apparatus deserves particular attention. The purpose of this paper is to propose a novel design of a magnetic circuit based on the Halbach array, which generates a uniform flux density inside the test specimen for the measurement of rotational core loss. The proposed design is simulated and prototyped, and experimental tests are performed on two different samples of M19 gauge-24 and M36 gauge-29 silicon steel at three different frequencies (60 Hz, 400 Hz, and 1 kHz). The field-metric method is used in this work to evaluate the rotational core losses.

Comparison of Different Demagnetization Models of Permanent Magnet in Machines for Electric Vehicle Application

The knee point in the B-H curve of a permanent magnet (PM) is considered crucial in electric motor applications. In the case of severe fault conditions, such as overheating or a short circuit in electric motors, the working point might fall below the knee point causing irreversible demagnetization of the PM. Hence, the remanence flux decreases and the motor operation would be reduced or stalled. In this paper, two demagnetization models of PMs are investigated, i.e., a linear model and an exponential model. Demagnetization curves for NdFeB were measured at temperatures varying from room temperature to 180°C. It was found that all the parameters in the exponential model, including Br, Hjc, μr, and the fitting parameter K1, are temperature dependent. Therefore, an exponential model can be developed as a function of temperature which allows a more efficient implementation within electric motor applications using PMs. However, comparison of the exponential and linear models indicates that the latter has a better accuracy near the knee point for the demagnetization curves of NdFeB magnets.

Design of a novel test fixture to measure rotational core losses in machine laminations

The need for testing magnetic materials used in electric machine laminations and measurements under a rotating field is of importance in machine design. In order to obtain satisfactory experimental data, the design of the measurement apparatus deserves particular attention. The purpose of this paper is to propose a novel design of a magnetic circuit based on the Halbach array, which generates a uniform flux density inside the test specimen for the measurement of rotational core loss. The proposed design is simulated, and experimental tests are performed.

Effect of Shear Cutting on Microstructure and Magnetic Properties of Non-Oriented Electrical Steel

In manufacturing electrical machine cores, the electrical steel laminations are often mechanically cut, leading to residual stress and a deterioration in magnetic properties. Several cutting techniques are used in the industry, such as shear cutting, punching, and laser cutting. The influence of shear cutting on the steel microstructure and magnetic properties was investigated in this paper. A single sheet tester was used for the measurements of two different grades of non-oriented electrical steel at different induction levels (0.1-1.5 T) and a wide range frequency (3 Hz-1 kHz). A scanning electron microscope was used for the characterization of the microstructure (grain size) at the cutting edges. The mechanical properties near the edge of the lamination were measured using nanoindentation. An increase in magnetic loss due to cutting was observed to be ~20% for B35AV1900 and ~9% for 35WW300, corresponding to a damaged area extending up to a distance of ~170 and ~140 μm, from the cut edge, respectively.

The effect of tooth-width on the distribution of rotational core losses

This paper examines the effect of tooth-width in the mapping of pulsating, elliptical and rotational losses in a tooth body for a given slot-pitch. Core loss distribution in the tooth is done with the use of FEA and 2-D core loss measurement results. The core loss distribution is computed using two methods, i.e., pulsating losses assuming all the flux-density in the stator is pulsating and elliptical losses including rotational losses. The two are compared and discussed in detail. A methodology that reduces the FEA geometrical size for core loss analyses to a slot-pitch is also presented.

The impact of rotating field on core loss estimation in electrical machine laminations

An investigation and analysis of core losses in rotating AC machines shows that the stator is subjected to different types of flux density including pulsating and rotating. The rotating flux can be elliptical or circular. This paper describes the influence of different flux patterns on core loss estimation. Three different machines are simulated to calculate the zones of rotating flux density in the stator cores of these machines. Experimental tests are executed using a new magnetizing circuit based on an electromagnetic Halbach array which is able to generate different types of flux patterns with different frequencies. Furthermore, the percentage error made by assuming all flux is pulsating is calculated.

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.

Magnetic core losses measurement instrumentations and a dynamic hysteresis loss model

Three typical types of magnetic lamination core loss measurement methods, the toroid tester, the standard Epstein frame and a single sheet tester, are first reviewed. Results of four types of testing (previous three plus a new Epstein frame for high flux density and frequency) are presented and compared. Comparisons among the measurements of different frames show discrepancies in the loss results. A general dynamic hysteresis core loss model is also presented. The model can calculate core losses based on the input parameters obtained from experimental measurements at only one single frequency in a thin lamination. The developed dynamic hysteresis model is simple and efficient, and has been shown to be very accurate compared with experiments.

Calibration of the Tangential Coil Sensor for the Measurement of Core Losses in Electrical Machine Laminations

The measurement of core losses in electrical steel laminations is considered an essential step in the machine design process. Accordingly, the calibration of the tangential field sensor for measurements of magnetic field strength H is of importance in core loss measurements for estimation of electrical machine efficiency. Due to the stray field between the lamination surface and the tangential coil, a concern is raised regarding the certainty of the measured field. This paper presents a reliable technical approach to calibrate the tangential field sensor used in the investigation of core losses in electrical machine laminations, which compensates for the drop in the actual field value. The proposed approach is based on developing a magnetizing circuit, which consists of two test laminations. An array of Hall Effect sensors is used in this study as a reference for the tangential field. The calibration results show that the magnetic field strength measured at the specimen surface by the tangential coil is scaled down by 4.57% of the actual field. The results are verified experimentally and validated by finite-element simulations. Based on the obtained results, a correction factor is applied on pulsating and rotational core losses to attain more accurate data.

The minor hysteresis loop under rotating magnetic fields in machine laminations

In rotating ac machines, the saturated flux density waveforms contain harmonics, which create minor hysteresis loops. The minor hysteresis loops in machine laminations constitute an additional loss which requires modifications in traditional core loss formulas. This causes a serious challenge in core loss estimation. The task becomes more competitive under rotating magnetic fields, where the minor loop behavior has not been investigated yet. This paper highlights the problem of harmonics in rotating fields and its effect on the core loss estimation. In addition, the behavior of minor loops under rotating fields is compared with the minor loops under pulsating fields. Measurements were carried out on a nonoriented silicon steel sample of M36G29 with different fundamental frequencies of interest to the industry, 60 Hz and 400 Hz, with consideration of the third harmonic at each frequency. A design of magnetizing test fixture based on an electromagnetic Halbach array is used to perform these measurements. Results are presented and discussed.