Power transformers are critical components of the electrical grid, and the insulation status of their windings is directly linked to the operational safety and reliability of power supply. Short circuits at the low-voltage side outlets can easily damage the inter-turn insulation, leading to inter-turn short circuit faults in the windings. To further study the transient processes of inter-turn short circuits and low-voltage side outlet short circuits in transformer windings, this research investigates the weak links in heat generation and mechanical stresses, and elucidates the mechanisms of insulation failure development. An electromagnetic-force coupled model, congruent with the actual structural dimensions of the transformer, was developed. Utilizing finite element simulation software, the electromagnetic transient processes of the windings under various operational conditions were examined. A comparative analysis of the electromagnetic force distribution characteristics was conducted to explore the influence of different fault conditions on winding insulation. The results indicate that during inter-turn short circuit faults in transformer windings, the current in the short-circuited turn significantly exceeds that in three-phase outlet short circuits. Compared to normal load conditions, the peak currents through the short-circuited turns and overall windings increased by 5 318% and 3 314%, respectively; the maximum magnetic field intensity rose by 1 511% and 2 111%, and the peak electromagnetic force density on the winding turns surged by 5 210% and 11 489%. Inter-turn short circuit faults in transformer windings are likely to severely damage the insulation, whereas three-phase outlet short circuits can lead to unstable deformations and degradation of insulation.