Vibration characteristics of a single-phase four-column auto-transformer core excited by geomagnetically induced currents

During geomagnetic storms, geomagnetically induced currents (GICs) occur in the power grid. GIC is a quasi-direct current, which is represented by using a fixed DC current, the authors propose an approach that combines field-circuit-coupled and weakly coupled magneto-mechanical models to investigate the magnetostriction characteristics of single-phase, four-column autotransformer cores excited by GICs. A non-linear magnetostrictive constitutive model that considers the impact of stress and magnetisation intensity on ferromagnetic materials is introduced. The model reveals that the strain in the core initially increases as the magnetisation intensity increases; however, when the core begins to saturate, the magnetostrictive strain weakens as the magnetisation intensity increases. Moreover, the results of multiphysics finite-element modelling are experimentally verified using a direct current bias platform. The results show that when excited by GICs, there is an enhancement in the vibration of the iron core, and the harmonic content of the vibration acceleration increases considerably, with the odd harmonics most significantly increasing in amplitude. The conclusion drawn is that GICs can exacerbate transformer vibration and significantly increase the content of harmonics, especially odd harmonics.