Measurement of rotational iron losses in electrical sheet

A large portion of the stator core of a rotating electric machine is subjected to magnetic flux that rotates in the plane of the laminations. Iron losses under rotating flux conditions can differ considerably from those due to alternating fields. It has long been suspected that this difference may be responsible for some of the discrepancy between predictions of no-load core loss at the design stage and values obtained by factory test. At present, no international standard exists for determining iron losses due to rotational flux. This paper describes an apparatus capable of making such measurements and briefly reviews the state of the art in this area of research. Measured loss curves are given for seven grades of nonoriented (NO) electrical sheet.