Articles techniques et présentations

The aim of this work is to compute the mechanical forces in a 12-pulse converter transformer winding in different short-circuit modes. A 12-pulse converter transformer is a three phase transformer with two secondary windings whose tension have 30° phase displacement and one primary winding. The secondary windings feed a doble 6-pulse rectifier diode bridge, typical circuit configuration is shown in Figure 1. In case one diode of the input rectifier is faulted and becomes short-circuited, the converter transformer can be subjected to a dynamic short circuit stress being higher than that due to a fault occurring on the DC-link (equivalent to a three-phase short circuit on both secondary windings). A parametrized geometry 2D axisymmetric was used to compute the Lorentz forces, in particular the Magnetic Fields interface of the AC/DC Module was used to compute magnetic field and induced current distributions in and around the windings, in this way is possible to obtain the exact Lorentz forces distribution (radial and axial). An important advantage of choosing COMSOL is the fact that magnetic calculations are easily coupled with mechanical simulations through the export of electromagnetic forces