The FEM Analysis of Magnetic Field in Converter Transformers During Faults

The rectifier transformers during internal faults in valve sets undergo strong submagnetization with DC, saturating its core. Simultaneousely the nonsymetrical short circuit conditions produce large amount of currents in both windings. The core in instants of high saturation loses its “magnetic mirror” properties and the main flux finds its way as well in the nonmagnetic space out of the core. The configuration of leakage flux varies in function of time and contains the DC component fast increasing with time. This conditions greatly differ with classic understanding of leakage flux in usual transformers operating in networks during faults. The above phenomena can influence the electromagnetic field in transformer space, as well as the field of dynamic forces and the mechanical behaviour of windings. Evidently they deserve, a more detailed analysis. It must consider the magnetic properties of steel and should explain the difference of field distribution in convertor transformers in comparison to usual network units.