Enhanced modelling of multi-core cables and redefined calculation of its screen/sheath losses and internal thermal resistances.
With an important update introduced in November, the modelling of two- and three-core cables has been extended. Cableizer goes beyond the IEC and allows the use of screen and sheath simultaneously for all cables, which was possible already for single-core cables and has now been extended to multi-core cables. Additionally, for three-core cables, we introduced the selection of all possible combinations of common or separate screen and sheath:
With these changes, the blog entry Calculation of internal thermal resistances of multi-core cables from March 27, 2015 is no longer valid to a large extend.
These changes posed several challenges regarding visualisation of the cable in the preview, the separate calculation of the screen and sheath losses and last and most difficult the calculation of the thermal resistances for all possible cases with respect to bedding and serving of screen wires, the creation of isotherms through sheath layers and/or tape screens, possibility to have corrugated aluminium and copper sheath and the presence of armour layours.
Especially the formulas for the cable-internal thermal resistances have been updated significantly:
In contradiction to the new edition of the IEC, the calculation of $T_3$ is identical for all cases and only covers the thickness of the jacket and a potential additional layer on top. The influence of corrugation of the sheath (please refer to IEC 60287-2-1, chapter 220.127.116.11) and of the filler material for unarmoured three-core cables with separate tape screens (chapter 18.104.22.168) is covered in $T_2$ instead.
|common screen/sheath||separate screen & common sheath||separate screen/sheath|