Determination of magnetic properties of soft-magnetic ring cores with a reduced number of primary and secondary winding turns

Abstract

In the paper, a computer-controlled method for determination of magnetic properties of soft-magnetic ring cores is presented in detail. The method complies with the IEC 404-2 standard, which requires a sinusoidal magnetic polarization in the tested core. A special attention is paid to the influence of improper ring core data - especially the filling factor - and to the reduction of primary and secondary winding turns that results in a fast and secure connection of the specimen in the measurement circuitry. On the other hand, the reduced number of primary and secondary turns increases demands that need to be fulfilled by a power supply generating the magnetizing current. The paper explains how a sinusoidal magnetic polarization of the core is maintained and introduces solutions to avoid a premagnetized core and power amplifier instability. In order to raise the measurement accuracy and expand the measurement range, programmable gain amplifiers (PGA) were installed in both measurement paths as well as in the negative feedback control loop.