A conservative and simple current-rating algorithm is presented for buried power cables that are subjected to a cyclically varying load. The algorithm is based on the assumption that the moisture distribution in the soil is stationary during load variations and that it is determined by the spatial distribution of the maximum heat flux. This assumption is reasonable in view of the hysteretic nature of moisture retention by soils. Only one Fourier component of the heat-loss variation is considered in the algorithm. Applications are shown where adapted equations of Philip and De Vries are used to describe heat and moisture transfer. The critical temperatures that were found for drying-out of the soil hardly differed for stationary and cyclic loads. It appeared that the maximum allowed average load decreased with increasing load variation. On the other hand, at maximum load, the maximum current occurring during a cycle was higher than the maximum stationary load allowed.
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