Two-Zone Geological Soil Moisture Migration Model for Cable Thermal Rating

An optimized two-zone model based on the critical degree of saturation is proposed in this paper for ampacity calculations of underground power cables. Moisture migration is fully considered based on geological soil models. Comprehensive finite-element method (FEM) simulations are performed to study the effect of the moisture content and its effects on soil thermal resistivity and critical temperature rise. The critical degree of saturation (S
_cr
) is used in the improved two-zone model instead of the critical temperature rise (Δθ
_x
) used in the IEC Standard 60287. The comparative analysis presented between the new method and the IEC Standard shows that IEC is more susceptible to changes in the ambient conditions. The use of a fixed critical temperature rise may yield significant errors. Shortcomings of numerical solutions are discussed highlighting the advantages of the new (optimized) two-zone model. The optimized method is useful for the design of new installations as it accounts for changes in soil thermal resistivity and critical temperature rise. The new method has been validated with available test results.