In this paper the traditional enlargement law for AC cables - based on the so-called “volume effect” - is extended to DC cables via an innovative theoretical approach, that takes into account some aspects peculiar of HVDC cables, i.e. the dependence of the electric field profile on volume electrical resistivity of the insulation, the associated dependence of volume resistivity on electric field and temperature, the role played by the heat dissipated through the cable layers and by the thermal resistivity of the insulation. An application of the novel enlargement law developed is given in the paper considering real HVDC cables and examining the influence of some of the many parameters appearing in the model.
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