HTS transformers leakage flux and short circuit force mitigation through optimal design of auxiliary windings

Abstract

Mitigation and control of leakage fluxes and short circuit forces needs much more attention, for a high-temperature superconducting (HTS) transformer, than for a conventional one. Different methods such as the application of auxiliary windings, multi-segment winding, and flux diverter have been presented in the literatures for leakage magnetic field reduction in HTS transformers. In this paper, for the first time, optimal design of auxiliary windings has been performed for a 132/13.8 kV, 50 MVA three phase core type HTS transformer. Genetic algorithm (GA) has been used for the optimization process. Induced current in auxiliary windings which is inversely proportional to the leakage fluxes and short circuit forces has been considered as the objective function. An analytical method has been proposed in this paper which formulates the objective function in terms of the self and mutual inductances of the main and auxiliary windings. Consequently, the optimal parameters of the auxiliary windings have been determined. It is shown that utilizing the optimized auxiliary windings design, the leakage fluxes, the radial and the axial components of the short circuit forces are reduced significantly. Two-dimensional electromagnetic field simulations using finite element method (FEM) by application of COMSOL multiphysics software have verified the theoretical formulations.