Iron Losses in Elliptically Rotating Fields

Abstract

Power frequency losses in silicon iron alloys due to an elliptically rotating magnetic field have been measured by a calorimetric technique and predicted approximately using a simple model. Previously reported experiments for measuring these losses fail to approach saturation and have doubtful field unformities. A thin disk-shaped specimen is placed in the elliptically rotating field of a set of two phase air-cored rectangular Helmholtz-type coils. The 60-cps rotational loss is calculated from the initial rate of specimen temperature rise sensed by a copper-Constantan thermocouple attached to the disk. The thermocouple output is amplified and recorded with an accuracy of 10−3°C. The field coil system produces fields uniform to 2% in a 1.0-in.-diam. region and of strengths up to 250 oe, which is sufficient to approach saturation in 0.005-in. thick by 0.875-in.-diam disks. The losses have been measured for grain oriented and single-crystal materials with all materials showing a decrease in loss for an increase in flux density for large, nearly circular fields. The losses for elliptical magnetization may be approximated with a simple model composed of a mixture of lossless domain rotation, eddy current loss, and alternating hysteresis loss proportional to an alternating flux. This model is intended only for the calculation of rotational hysteresis losses and not to explain the origin of these losses. The calculated and experimental losses agree for all amplitudes and eccentricities of magnetization to within 40% for rotation in the (100) plane with the worst discrepancy for circularly rotating magnetization.

Measurement and Modeling of Rotational Core Losses of Soft Magnetic Materials Used in Electrical Machines: A Review

“…That is why this method is known as the watt-metric method. With the development of digital techniques, H and B waves can be readily obtained in numerical form, and core losses can then be calculated by using (10). An outstanding advantage of this method is the simplicity in determining H.…”

“…In 1962, Strattant and Young [10] studied the power frequency losses in silicon iron alloy due to an elliptically rotating magnetic field with disk samples placed in the center of two perpendicular pairs of rectangular Helmholtz-type aircored coils, and predicted the losses approximately using a simple model without physical basis: where B 1 and B 2 are the major and minor axis flux densities, B s is the saturation flux density, P 1 and P 2 are the alternating hysteresis losses in the major and minor axes for peak flux densities of B s , respectively, and P 3 is the eddy current loss for a peak flux density of B s . However this model only simulates the core loss with elliptically rotating magnetic fields, while the basic physical phenomena were not described.…”

1-D and 2-D Loss-Measuring Methods: Optimized Setup Design, Advanced Testing, and Results

“…This fact, in conjunction with a certain experimental complexity, is the main reason for the substantial discrepancies found in the results from different laboratories [52] [53]. In early attempts to measure the 2D magnetic losses, either cross-shaped samples with orthogonal pickup coils [55] [56] or disk samples placed at the center of two perpendicular rectangular Helmholtz pairs coils supplying a maximum magnetic field strength around 20 kA/m [57], were tested. Nowadays, the Rotational Single Sheet Testers (RSST), of either vertical or horizontal type, are typically employed.…”

“…With the additional knowledge of the local flux density and the usual integration of their product, the loss figure is obtained. This is the rule for 2D loss measurement, but it is in some cases associated with or substituted by the thermometric method [57], where the increase of the sample temperature upon energy dissipation is measured.…”

State-of-the-art and future trends in soft magnetic materials characterization with focus on electric machine design – Part 1

“…Among this standard method, other methods for testing of magnetic materials by 1-D magnetic field have been considered in this article [20,21]. Additional attention has been given to the measurement methods for testing of magnetic materials in multi-axial magnetic field, especially in rotational field [3,5,7,25,31,39,44,45,47,48]. These modern techniques are mostly devoted to the more comprehensive investigation of power loss that occur in the materials when rotational magnetization is present.…”