Examination of magnetic properties of nonoriented electrical steels using ring-type specimens

Abstract

The Epstein frame test is commonly used for investigating the magnetic properties of electrical steels because of the convenient sample preparation. This test requires the samples to be cut half-parallel and half-perpendicular to the direction of rolling to account for the magnetic anisotropy of the sheet. An alternative method to evaluate the magnetic properties of electrical steels is the ring core test. This test more closely represents the magnetic cores in rotating machinery such as motors and generators because the sample shape for this test resembles the practical rotating applications. The measured results may vary according to the test methods. In this study, the differences between the results of the Epstein frame tests and ring core tests were investigated for the various grades of NO steels. For the magnetic induction measurements, results of the ring core test showed a trend of lower values than in the results of the Epstein frame tests. The core losses measured by the ring core tests are generally greater than those of the Epstein frame tests. The difference in results due to the test methods can be attributed to the anisotropy parameter, A(h), which can be obtained from the crystallographic texture of the sheet sample. The difference becomes significant when an area fraction of the texture component shows a high 1-A(h) value by the Epstein test but a low value by the ring test.