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

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.