Experimental Investigation on Cumulative Effects of Transformer Winding Deformation Under Short‐Circuit Impulses

ABSTRACT Power transformer windings are susceptible to deformation after multiple short‐circuit impulses, threatening power grid stability. Currently, there is a lack of experimental data on various characteristic parameters of failures after multiple short‐circuit impulses. To investigate winding deformation and its gradual deterioration, a mock‐up transformer was constructed to study the cumulative effects. Short‐circuit tests were conducted under different current ratios, and the cumulative effect was quantified based on short‐circuit impedance and axial force variations. A correlation was established between different current ratios, impulse number and cumulative winding deformation. The cumulative effects of winding deformation are categorised into four levels: none, minor, significant and severe. Thresholds indicating severe deformation and degraded short‐circuit withstand ability are defined by an absolute impedance change rate exceeding 1.1% and a relative rate exceeding 0.3%. Additionally, an axial force change rate of ± 20% serves as an early warning indicator, providing greater sensitivity to detecting impulse effects on winding stability compared to impedance change rate. Monitoring impedance and axial force changes provides a reliable approach to assessing transformers affected by the cumulative effects of short‐circuit and identifying the risk of winding deformation.