Examination of Magnetic Properties of Magnetic Materials at High Temperature Using a Ring Specimen

The magnetic properties of magnetic materials are considerably changed near the Curie temperature. In order to analyze the magnetic characteristics of magnetic devices which operate at high temperature, such as induction heater of billets, high temperature motor, the B-H curves and iron loss curves are necessary for the precise analysis. But, the reports of the examination of the measuring method and the behavior of such magnetic properties are few. In this paper, the measuring method of magnetic properties at high temperature is investigated. It is shown that the permeability is not changed so much under about 500°C in the case of nonoriented electrical steel. However, it changes drastically above about 500°C. The iron loss decreases with the increase of temperature. The decrease of iron loss is mainly due to the decrease of hysteresis loss with the increase of temperature.