2-D Finite-Element Electromagnetic Analysis of an Autotransformer Experiencing Ferroresonance

The key concern for transformers experiencing ferroresonance is whether the energy transferred into the transformer body during core saturation by the nonsinusoidal currents is damaging. Saturation and the consequent incompetency of the core to contain the flux manifests itself as current induced in parts of the transformer body not foreseen to conduct current. Sustained ferroresonance may last for minutes (or even hours), when no intervening operations are carried out, and may cause local overheating and thermally degrade surrounding insulation. In this paper, transient electromagnetic analysis was conducted by using 2-D finite-element models of a 240-MVA 400/132/13-kV autotransformer. As a continuing effort, the main objective of modeling is to visualize the flux flow in parts where transformer designers have not anticipated its presence. A quantitative assessment of the flux, the induced currents, and the power dissipated in these parts has been carried out to determine the degree of risk imposed on a transformer under ferroresonance.