Real-time Calculation of Transient Ampacity of Trench Laying Cables Based on the Thermal Circuit Model and the Temperature Measurement

Considering the large heat capacity of the surrounding soil, the influence of cable load on the transient temperature rise of the soil can be neglected within short periods of time. A simplified transient thermal circuit model based on the monitoring ambient temperature in the trench is proposed. The thermal resistance and thermal capacity of the model are calculated by using the empirical formula. Considering the strong thermal interaction between multiple loops of the cables, the external thermal resistance is modified by the load and air temperature. By comparing the result of the calculation of the model with that of the finite element method, the accuracy of the thermal circuit model is verified. Based on the method of the transient thermal circuit model, the maximum permissible current-carrying can be predicted.