Nonlinear Fatigue Damage Assessment for Transformer Windings Under Thermal Aging and Repeated Short-Circuit Loading

Transformer winding failures are driven by the cumulative degradation from repeated short-circuit shocks rather than a single extreme event. Current standards rely on static strength checks using as-manufactured material properties, ignoring both thermal aging and load-history effects. To address this gap, we propose a nonlinear fatigue cumulative damage framework that couples a long-term thermal-aging spectrum, converted into an equivalent aging duration and a global property correction, with a micro-spectrum of individual short-circuit events, discretized into an eight-level variable-amplitude stress history. The resulting six-step workflow shifts the paradigm from passive strength checking to proactive life management, offering utilities a physics-informed framework for estimating the residual fatigue life of aging transformers.