An improved formula for external thermal resistance of three buried single-core metal-sheathed touching cables in flat formation

An improved formula for the assessment of the external thermal resistance of three buried single-core, metal-sheathed, touching cables, laid in a flat formation, is proposed. The formula arises from the analysis based on a coupled electric-thermal model, as well as on the stochastic optimization method based on differential evolution. The effect of the new formula on cable rating is illustrated in a numerical example. Index Terms--External thermal resistance, numerical modeling, optimization methods, underground cables.