Using multiple modes to reconstruct conductor locations in a cylindrical model of a power transformer winding

Abstract

A study of a novel method to detect mechanical deformations of windings in a power transformer, while in operation, is presented. We employ an approximate model of a transformer winding surrounded by the transformer-tank wall and the magnetic core. The transformer winding is viewed as a structure consisting of thin conducting cylindrical rings (winding segments or turns) situated within a coaxial cylindrical waveguide, where the inner conducting cylinder represents the iron core that conducts the magnetic flux and the outer conducting cylinder represents the wall of the transformer tank. The basic principle is to insert antennas inside the transformer tank above and below the winding to radiate and measure microwave fields that interact with the metallic structure and the insulation. The responses from the radiated waves are assumed to be sensitive to any mechanical deformations that could be caused by electromagnetic forces due to short-circuit currents and possible manufacturing weaknesses. The goal is to be able to determine the radial locations of the individual winding segments or individual turns from measurements of the scattered fields at both ends. The propagation problem is solved by conventional waveguide theory, including mode-matching and cascading techniques. We utilize optimization as a suitable method to solve the inverse problem and obtain a good agreement between the reconstructed and true positions of the winding segments.