Research on Rapid Verification Method of Overload Protection Characteristics of Low-Voltage Electrical Appliances Based on Thermodynamic Equivalence Model

Conventional overload verification of bimetallic protection elements requires long-duration current loading and considerable time and energy consumption. This study proposes a rapid verification method combining a first-order thermodynamic equivalence model with image-based deflection measurement. Local linear interpolation between adjacent measured frames was used to determine the energization time corresponding to a prescribed target deflection. A current-dependent empirical correction factor was introduced to compensate for systematic deviations caused by simplified lumped thermal parameters and test-specific thermal boundary conditions. The model was identified using one target-deflection dataset and evaluated at two additional target deflections without parameter re-identification. Repeated tests were also conducted to assess cycle-to-cycle stability. The results show that the corrected model substantially reduced the temperature-rise deviation, maintained good prediction consistency across different target deflections, and exhibited low cycle-to-cycle variability. The method provides a physics-informed semi-empirical framework for rapid evaluation of bimetallic-strip overload characteristics. Further re-identification and assembled-product validation are required when the specimen configuration or thermal boundary conditions change.