Calculation of the internal thermal resistance and ampacity of3-core screened cables with fillers

摘要

All 3-core cables require fillers to fill the space betweenninsulated cores and the belt insulation or a sheath. The equations givennin IEC 287 and in the Neher-McGrath paper (1957) for the internalnthermal resistance of 3-core cables were developed for paper insulatedncables. For such cables, it was assumed that the insulation and fillernmaterials have the same thermal resistivities. In reality, in 3-corencables a variety of materials are used as fillers. The majority of thesenwill have a higher thermal resistivity than the insulation. In thenprevious paper, a new formula was developed to compute the value of theninternal thermal resistance of belted cables taking into account thenthermal resistivity of the filler. In this paper, screened cables arenconsidered and a new formula for the computation of the internal thermalnresistance of such cables is presented. The effect of filler resistivitynon cable ampacity is also discussed