Apparatus for loss measurements under multidirectional and dc-bias flux in electrical steel laminations

Abstract

Conventional standardized power loss measurements for electric steels are performed at flux densities with a single sinusoidal and unidirectional excitation. However, the flux inside electrical steel laminations can deviate significantly from the standard condition, and the loss is sensitive to such deviations of the flux in time and space. In this article, we describe the design and construction of an apparatus for loss measurements under two scenarios: (1) The main flux in the rolling direction is superimposed with flux in either the transverse or normal direction, while varying magnitude and phase angle between two fluxes and (2) the main flux having a dc-bias. The main flux in the rolling direction is generated in a square lamination frame by the current in excitation coils. The transverse and normal direction fluxes are generated by the current in auxiliary excitation coils wound around powder cores. The dc-bias flux is created either by an ac current with a small dc offset in the excitation coils or by a separate coil excited by a dc current. We implement and compare the two dc-bias methods and discuss the commons and differences. Finally, we present experimental results showing the possibilities for loss measurements under the combined action of magnetic flux in different directions and under dc-bias.