Behavior of a single phase grid transformer during out-of-phase synchronizations

This paper focuses on a basic research of out-of-phase synchronization currents of a single phase transformer and its impact on a system of synchronous machine, transformer, switch and grid. The effect of transformer saturation is studied for different switching conditions using the finite element software FLUX 3D. The position of the switch has a significant influence on the peak current. The studied phenomenon is from special interest in the case of an out-of-phase synchronization (OOPS) of turbine-generators. Therefore the synchronization on the side of a synchronous machine (LV-Side) and on the side of the grid (HV-side) are examined for different error angles of a single phase test arrangement. This first investigation shows that the occurring peak current on the side of the generator is lower, if the synchronization switch is placed on the HV-side. In this case the saturation of the transformer is negligible and the transformer can be modeled as a constant reactance. If the switch is placed on the side of the grid, the saturation of the transformer has to be regarded. These results have to be verified by a further study of a three-phase power transformer.