Measuring impedance frequency characteristics of magnetic rings with DC-bias current

This paper reports on a comprehensive study on a measurement method for the impedance characteristics in the frequency domain of magnetic rings as a function of DC-bias current up to saturation. The reported measurements in a one-wire coil arrangement with DC-bias current reproduce the operating conditions of rings used in high-power equipment and are useful for the development of circuit models used in power system simulators. The method and its key features are shown on an example of a nanocrystalline ring with large physical dimensions relevant for heavy power equipment. Low magnetic permeability of the ring material and large size of the ring were chosen as the most challenging case with respect to measurement system arrangement, allowing us to highlight the key aspects of the method. The measurement results are reported for frequency ranging from 50 Hz to 30 MHz and for the DC-bias current up to 800 A. The problems and difficulties encountered are highlighted and discussed how they were controlled and overcome.