Research on a Universal Analytical Thermal Circuit Model for Civil Electric Cables

The measured standard resistance at 20 °C ($R_{20}$) is a critical indicator for evaluating the quality of electric cables. Utilizing a thermal circuit model allows for the rapid determination of $R_{20}$. Focusing on civil electrical cables, this study constructs a thermal circuit model based on an equivalent circuit. Through mathematical derivation, model parameters are expressed as functions of the insulation cross-sectional area and conductor specification. Subsequently, the insulation area is fitted to the conductor specification, establishing a universal analytical thermal circuit model with the conductor specification as the sole variable. Ambient temperatures measured under specific operating conditions showed exponential variation. Using corresponding simulated conductor temperatures, the Differential Evolution algorithm was employed to train the model, achieving a training standard deviation of 0.0184 °C. Validation under different conditions demonstrated that for various cable specifications, the conductor temperature prediction deviation within 300 s remained within 0.368 °C, and the maximum estimation error for $R_{20}$ was less than 0.148%. These results indicate that the established model possesses high calculation accuracy and strong universality, offering a valuable tool for researchers and practitioners in fields relevant to civil electrical cables.