Mechanical method of iron loss measurement in a rotational field and analysis of iron loss in a motor

Abstract

A mechanical method of iron loss measurement in a rotational field was developed and, using this method, the mechanism of iron losses of motor cores was investigated. Iron losses in rotational fields of angular velocity ω(rad/s) induce torque T (Nm) in specimens, and the total losses are calculated from ωT. This new method of iron loss measurement is unrestricted by the configuration of specimen and the exciting conditions, and the iron losses of cores can be measured in the condition used in the motor. Using this new method, the iron losses of 0.5-mm-thick nonoriented electrical steels with 0.3% and 3% Si were measured in rotational fields at frequencies of 50–900 Hz. In disks, the ratios of iron loss in a rotational field to that in a one-direction field decrease as induction increases. The ratio is about 2 at less than 1T and becomes about 1 or less as induction approaches saturation. The effects of teeth on iron loss were investigated. The iron losses of a core with teeth are higher than those of a disk, and increase with lower Si and higher frequency. Iron losses at the teeth are larger than at the other parts, and increase with lower Si and higher frequency. The increase in iron loss is caused by the eddy current loss due to the flux wave form distortion and the flux concentration near the teeth and by hysteresis loss due to the flux distribution which is not uniform near the teeth.