VNIIKP RF TF Cable Untwisting and Elongation Under Tensile Force

To form a cable-in-conduit conductor (CICC) a cable should be inserted into a jacket under tensile force that is increasing with length of insertion. This tensile force can lead to both elongation and untwisting of a cable with increase of a twist pitch. The untwisting can also be induced by stress accumulated in the material during the cabling process. Understanding the untwisting process is very important, because the twist pitch of a cable inside a CICC strongly affects properties such as ac loss. In this paper, we present the results of an experiment on RF toroidal field (TF) cable sample tensile tests using the ≪Hitachi Cable≫ (Japan) tensile machine, and also the results of an experiment performed at the jacketing line in the Russian Scientific R&D Cable Institute (VNIIKP) after TF cable reinsertion. In the latter experiment, twist pitches were measured along the full cable length. A model to calculate untwisting and stretching processes has been developed. The results of the calculations are compared with the experimental data.