An on-line method to detect radial mechanical deformations of power transformer winding turns is presented. First-order perturbation theory is applied to a transformer winding surrounded by the transformer tank wall and the iron core. The transformer winding is modeled as thin conducting cylindrical rings (winding segments or turns) situated within a coaxial waveguide, where the outer conducting cylinder represents the transformer tank wall while the inner conducting cylinder represents the iron core. Antennas which radiate and measure microwave fields are proposed inside the transformer tank in order to identify and quantify the mechanical deformations of winding turns. The direct propagation problem is solved using conventional waveguide theory with mode-matching and cascading techniques. An optimization algorithm is then used to solve the inverse problem whereby a good agreement between the reconstructed and true deformations of the winding segments is obtained.
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