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.