The Influence of Complex Permeability on the Broadband Frequency Response of a Power Transformer

This paper considers the effect of the complex permeability of a power transformer core on the frequency response analysis (FRA) test spectrum. Current work in FRA generally neglects the core beyond a few hundred kHz. This research demonstrates that the effective complex permeability is significant at 1 MHz and greater than unity at frequencies exceeding 15 MHz. The paper also shows that for broadband small signal testing, such as FRA, the low field conditions induced by the injected signal result in a relative permeability that approaches the initial permeability of the core. This ensures that the relative permeability remains approximately constant over a large range of frequencies and will have a degree of independence with respect to the amplitude of the injection voltage.