A path of power transformers failure under multiple short-circuit impacts

Abstract

In this study, a positive feedback loop between gap occurrence during vibration and residual deformation of spacers is identified, based on which a transformer failure path under multiple external short-circuit impacts is demonstrated. A three-stage analysis is performed. First, two prestress application methods, namely, elastic and fixed methods, are differentiated. The nonlinear and nonstretchable characteristics of spacers are illustrated. The criterion of gap occurrence in the fixed-application method is investigated. A case study is conducted to analyze the possibility of gap occurrence. Subsequently, the effect of the gap on the vibration process is analyzed. Owing to the gap, the vibration intensity of the entire winding is amplified, and the stress on the conductors and spacers is exacerbated. The mechanism of this phenomenon is explicated. Finally, based on the experimental results in which the amplitudes of cyclic loads first increase and then decrease, the unidirectional change in the residual deformation is observed. Under cumulative impacts, the residual deformation is greater, and the gap occurs more easily, thus contributing to the winding collapse under multiple short-circuit impacts.