Page 45 - Analysis Report of Global Market in the Submarine Cable Field (2017)

Spiral winding angle is generally less than 30°. But for the flexible HVDC 3.3 Bending performance design
submarine cable, the limitation of its structure, performance and the The flexible HVDC cable subjected to bending load frequently during
production process, adopt a diameter of 6 mm galvanized steel wire operation, it needs good bending flexibility, the bending performance
armored for the conventional elastic modulus of 200 GPa, the number design is very important. In order to improve the performance of the
of galvanized steel wire 75 and spiral armoring is one layer, which makes whole cable bending, the following points in bending performance
the type (2) tensile design parameters can be adjusted the only armored design should be considered: a. Internal metal conductor to be spiral.
spiral angle. Formula 2 shows the flexible HVDC cable sheath (diameter b., The outer armored wire layer of armored spiral angle can not be too
6 mm galvanized steel wire armored layer 75 elastic modulus is 200 GPa) small. In order to make the tensile reinforced flexible HVDC submarine
change of tensile stiffness with armored helix angle curve. Final steel cable design to meet the design index of bending performance. Using the
wire armored spiral angle is 18.6° can obtain the cable tensile stiffness following formula to design flexible HVDC cable armoring layer flexural
550 MN, which meet the design requirements of the tensile performance rigidity Kb,a,
of flexible HVDC submarine cable.
Figure 2 Tensile rigidity of armoring layer with the helix angle Change
curve In formula (4) The unit of Kb,a is kN•m , I i is the moment inertia of the
2
single spiral armored steel wire layer i and vi is the flexural cross section
coefficient of the single spiral armored steel wire of layer i.

It is limited by its structure, properties and production process, the
flexible HVDC cable armoring layer determined use diameter 6 mm
galvanized steel wire 75 elastic modulus of 200 GPa one armor layer,
which makes the formula (4) bending design parameters can be adjusted
only armored spiral angle. Fig. 4 shows the curve of the bending stiffness
with the spiral angle of the armor on the basis of meeting the design
of tensile stiffness (i.e., the extent of the sheath helix angle at 10°~30°).
Final steel wire armored spiral angle of 18.6°, can obtain the cable
bending stiffness is 30.5 kN•m2, which can meet the design requirements
armoured spiral angle of the bending performance of flexible HVDC submarine cable.
3.2 Design of torsion resistance Figure 4 Curve of bending rigidity of armored layer with spiral angle
The flexible HVDC submarine cable is easily subjected to torsion
load during operation, the torsional angle is large, so the torsion
resistance design is very important. The armored layer of the
flexible HVDC cable can not only provide tensile ability, but also
can provide the ability of anti torsion. Using the following formula
design flexible HVDC cable armoring layer torsional stiffness Kn,a,

(3)
2
In formula (3): The unit of K na is kN•m J c G c means overall
torsional rigidity of center cable core.
It is limited by its structure, properties and production process, the
flexible HVDC cable armoring layer determined use diameter 6
mm galvanized steel wire 75 elastic modulus of 200 GPa one armor
layer, which makes the formula (3) torsional design parameters can armoured spiral angle
be adjusted only armored spiral angle. Fig. 3 shows a curve of the 3.4 Minimum breaking force design
torsional rigidity varying with the spiral angle of the armor on the In accordance with the provisions of the ISO 13628-5 3.1.32 the standard
basis of the design satisfying the tensile stiffness (i.e., the extent of armored units in the non bending stress failure criterion for failure of
the sheath helix angle at 10°~30°). Final steel wire armored spiral DC submarine cable structure, the flexible HVDC submarine cable
angle is 18.6° can obtain the cable torsional stiffness 290 kN•m2, minimum breaking force (tensile strength) design value should sum can
which is meet the requirements of torsion resistance design of withstand the maximum tensile force of each steel wire armored. Using
flexible HVDC submarine cable. the following formula to design flexible HVDC submarine cable tensile
force Fb,
Figure 3 Curves of torsion stiffness of armored layer with screw angle

In formula (5) Fb is the minimum breaking force of armored steel
wire, kN, and σsi is the yield strength of layer i steel wire. According
to the determined by tensile and torsional and bending properties of
the armored steel wire related parameters and the spiral angle can be
calculated by minimum tensile force of the flexible HVDC submarine
cable is 677 kN, which can meet the design requirements for the
minimum tensile force of flexible HVDC submarine cable.
armoured spiral angle
3.5 Min. bending radius design
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