Comparative analysis of the characteristics of outlet short circuit and winding insulation fault of distribution transformer and its preventive measures

Outlet short circuit on the low-voltage (LV) side and winding inter-turn short circuit faults are hazardous to transformer operation. To investigate the formation mechanism of winding insulation faults of distribution transformer, ANSYS Maxwell was used to build a coupled magnetic field-circuit model with the same structural dimension as the actual distribution transformer. An outlet short circuit and winding inter-turn insulation faults were set by using the voltage-controlled switch in the external circuit of the model. Subsequently, the differences in the electromagnetic characteristics and the electrodynamic force distributions of the windings under three operating conditions, namely, nominal load, three-phase outlet short circuit on the LV side and inter-turn insulation failure were studied, respectively. The results show that compared with the rated load, in the cases of outlet short circuit and inter-turn insulation faults, the amplitude of winding current increases by 20 and 50 times, the magnetic field strength grows by 20 and 17 times, and the electrodynamic force rises by 400 and 230 times, respectively. Outlet short circuit fault is more likely to cause the winding instability and deformation, and inter-turn short circuit fault can easily burn out winding insulation. Therefore, corresponding preventive measures were proposed.