Assessment of the Withstand Ability to Short Circuit of Inner Windings in Power Transformers Considering the Cumulative Effect

After transformers have been subjected to multiple short-circuit shocks, the support stiffness of the winding spars changes under repeated forces, which in turn causes changes in Withstand Ability to Short Circuits (WASC). This has rarely been taken into account in previous studies. In this paper, an analytical model of the transformer leakage magnetic field was developed and its validity was verified. Secondly, the effects of short-circuit shocks on the conductors and braces were explained by building a finite element model of the coils within the transformer winding for simulation. Finally, WASC of a 110 kV transformer was assessed. The results show that the safety factor for bending stresses in the conductor increases and the safety factor for critical loads decreases after being subjected to a short-circuit shock. The likelihood of flexure in the transformer winding increases. The conclusions can provide an important basis for the evaluating the WASC of transformers.