Double-Ladder Circuit Model of Transformer Winding for Frequency Response Analysis Considering Frequency-Dependent Losses

It is well known that power transformers inevitably suffer the impacts of short-circuit electromagnetic forces in service. For precise diagnosis investigation of winding mechanical deformation, this paper presents a double-ladder circuit model of transformer winding with lumped parameters for frequency response analysis. This advanced model includes the axial and radial ladder networks with regard to the winding disks and the eddy current paths of the magnetic core, respectively. In the radial ladder network, the nonlinear behavior of frequency-dependent parameters and core loss are considered. Relevant equivalent parameters in this double-ladder circuit model are calculated using the 3-D finite-element method. The energy balance method is applied to obtain the frequency-dependent inductances and resistances. In order to verify the effectiveness of this model, the frequency responses of voltage ratio at a wide frequency range from a few tens of hertz up to megahertz are simulated and measured.