Within the highly competitive electricity market, companies often reduce costs by using aging equipment and by overloading their transformers. These conditions substantially increase the risk of transformer explosions. These incidents are caused by electrical arcs occurring within oil filled transformers. The arc, within milliseconds, vaporizes the surrounding oil and the generated gas is pressurized because the liquid inertia prevents its expansion. The pressure difference between the gas bubble and the surrounding liquid oil generates a dynamic pressure peak, which interacts with the transformer. The reflections generate pressure waves that lead to transformer rupture since transformers are not designed to withstand these pressures. This results in dangerous explosions, expensive damages and possible environmental pollution. Despite all these risks, and contrary to usual pressure vessels, no specific standard has been set to protect sealed transformer tanks subjected to large dynamic overpressures.
In order to study transformer rupture and its prevention, experiments have been performed on transformers. However, safely carrying out live tests is difficult and expensive. In order to limit the costs, to reduce the risks and to gain insight on these phenomena numerical simulation tools are necessary. First a computational fluid dynamics solver was developed; it is based on an unsteady compressible two-phase flow model, the equations parameterizing the system are solved using a 3D finite volume method. Previous papers showed the ability of the hydrodynamic tool to study in detail (1) dynamic pressure wave propagation inside transformer oil that leads to transformer rupture and (2) depressurization induced by efficient protection means. Later, the hydrodynamic numerical tool has been one-way coupled with Code_ASTER, a dynamic structural analysis package, to create a fluid structure interaction (FSI). Preliminary results were shown and this strategy has been applied to the study of more complex electrical equipment.
The present paper’s goal is to illustrate the development and application of a two-way coupling for the aforementioned fluid structure interaction strategy. The methodology for the enhanced coupling is explained and the simulation results about the structural behavior caused by these dynamic pressures are presented.
