The principle of cable torsion and its impact on cables

In addition to the cable's self-rotation around the axis under the influence of its own weight and internal oil pressure, additional torsion is also caused by the torsional effect of the traction steel wire rope itself and the different curves in the cable path, such as up, down, left and right.

Torsion is detrimental to cable insulation paper and metal sheaths. Excessive twisting of cables can cause the insulating paper to wrinkle, become loose, and even break. However, there is no definite data on how much Angle to turn in order to minimize such adverse effects. In conclusion, the smaller the twisting Angle, the better.

The conductive core, radial reinforced copper tape and axial reinforced copper tape (or armoring wire) of single-core oil-filled cables have latent torque stress during the winding process. This stress is the root cause of torsion (i.e., untwisting or loosening) in the cable and determines the magnitude and direction of the cable's self-rotation around the axis. Especially when single-layer longitudinal copper tape armoring is adopted, the longitudinal armoring torque stress plays a dominant role in torsion. To accurately determine the Angle and direction of the cable torsion, a torsion test as shown in Figure 5-6-3 was conducted. The length of the test cable is 6.4 meters, with a cross-sectional area of 600mm ². It is armored with single-layer longitudinal helical reinforced copper tape, and the self-weight of the cable is 27 kilograms per meter. The upper end is suspended and fixed, and a load of 3 tons is applied to the lower end. The maximum torsion Angle at the suspension point is measured to be 100° to 110°. As the cables used in the test are relatively short, the torsion Angle may be even larger during actual laying.