Turning point in arc cooling: multiscale energy transport in high-current circuit breakers

Successful high-voltage current interruption critically depends on rapid pre-current-zero arc cooling, yet the physical onset of the transition from quasi-stationary energy balance to accelerated extinction remains poorly defined. In this study, this onset is formalized as the Turning Point of arc cooling (TP) and identified using a Jacobian-Trace-Based Cooling Intensity (JT-CI) framework. The framework resolves the transition into two complementary signatures: an Ohmic TP associated with global arc-column contraction and resistance growth, and a radiative TP associated with localized temperature-field restructuring induced by inward gas-blast impingement. Simulations show that, before the TP, Ohmic heating and radiative cooling maintain a quasi-stationary energy balance; after the TP, both mechanisms enter rapid-decline regimes, shifting the dominant heat-removal pathway toward convection and thermal conduction. The existence of the TP is further observed across 9-102 kA and varied chamber geometries, demonstrating its robustness while revealing its structural-aerodynamic sensitivity. Validation against 63 kA/T10 and T30 test duties (10% and 30% of the rated current) gives voltage and energy deviations below 10%. The proposed framework provides a physically interpretable temporal boundary for evaluating thermal interruption capability and guiding knowledge-based interrupter optimization.