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What is the procedure of reducing the sheath losses in sheaths of the three single core cables in a 3-phase system ?


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The sheath losses, which is proportional to the conductor losses, can be reduced by cross bonding the sheaths of the sheaths of the three single core cables. Since the three sheath voltages are 120° apart therefore in cross bonded cables the net sheath voltage will be zero when the single core cables are placed at the vertices of an equilateral triangle. Practically, in many cases the symmetry of the cable arrangement becomes impossible. In that case, the three voltages in series will not be quite balanced and some residual voltage will appear which no doubt results in the relatively small amount of sheath losses. In order to completely eliminate the sheath losses, the sheath voltages are balanced by transposing by transposing the cables as in case of overhead lines along with cross bonding.


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