A Novel Unsymmetrical Multi-Segment Concentric Winding Scheme for Electromagnetic Force and Leakage Flux Mitigation in HTS Power Transformers

The high axial and radial forces caused by short circuits can be very detrimental to high-temperature superconductor (HTS) windings of HTS transformers. Axial forces above the HTS winding critical value cause irreversible effects on the critical current reduction of an HTS tape. Such forces can disrupt the normal performance of HTS transformers and lead to quench phenomenon and insulation breakdown. Accordingly, any optimization in the design of HTS transformers that decreases the leakage flux and electromagnetic forces is very significant. This paper presents a novel method for reduction of leakage flux and thereby electromagnetic force in the windings of an HTS power transformer. First, concentric primary and secondary windings are subdivided into certain number of segments. In the next step, the proposed method, which is based on selecting the optimum distributive ratios for the created subwindings, is applied to the windings. In order to verify the effectiveness of the proposed method, an advanced finite-element method has been used. The method uses accurate and nonlinear E-J power law for defining the superconductivity characteristic. The results showed the efficiency of the applied method to mitigate the radial and axial leakage flux and thereby electromagnetic forces in the windings of the HTS transformer.