Electromagnetic force investigation on distribution transformer under unbalanced faults based on time stepping finite element methods

• In this paper the effect of short circuit current and also the effect of inrush current on the electromagnetic force have been investigated.
• The result of paper shows that the electromagnetic force obtained from 2Dmodels are different those obtained by 3-D models.

The occurrence of short circuit faults is a major cause behind the windings deformation in the transformers. Mechanical force is proportional to the square of the current. Hence under short circuit condition, it will be very high. These stresses radially or axially affect the transformer windings. Therefore, in the transformer designing, evaluating the effects of short-circuit current and inrush current is very important. In this paper, 2-D and 3-D time stepping finite element methods (TSFEM) that improved in Ansoft-Maxwell, are utilized as Instruments to investigate the leakage flux and electromagnetic forces due to short circuit and inrush current on the windings of 1000 kV A, 10/0.4 kV three-phase, three leg, distribution transformer. Electromagnetic forces in the transformer windings are produced as a result of combination between the current density and the leakage flux density in the winding regions. The study demonstrates that, especially, under single phase-to-ground short circuit fault, leakage flux density on the windings of transformer remarkably increase. The interaction between this high leakage flux with current density, causes the significant increase in the electromagnetic forces in transformer windings.