Transient Behavior of Power Cables Considering Partial Drying Out of the Soil

The thermal resistivities of the soil and backfill have decisive effects on the current rating of underground cables. An important factor is the possible formation of dry zones around the power cables due to moisture migration induced by thermal and moisture gradients. Whereas a calculation method for stationary and cyclic loads are described in the literature, there are no analytical methods for modeling of moisture migration taking into account changes in the load current over time. This is the main topic presented in this paper. A new analytical approach is presented in the paper, which allows analysis of the soil dryout phenomenon and its effect on cable rating when the cables are subjected to the load varying over time. The paper also reviews the existing two-zone model for the representation of the soil dryout phenomenon in the steady state cable rating calculations. The new developments introduced in this paper are illustrated by several numerical examples.