Page 46 - Analysis Report of Global Market in the Submarine Cable Field (2017)

Wire and Cable

The flexible HVDC cable can withstand tensile, bending and torsional 3.7 Numerical simulation
loads during installation and working process, in accordance with the The structure of the flexible HVDC submarine cable is more complex,
provisions of the relevant standards, in the bending process to yield based on the relevant theory on the design of mechanical properties,
strain of each unit failure criterion, take the maximum as the minimum further through the finite element analysis software of mechanical
bending radius of the whole. In the design of flexible HVDC submarine parameters of the design of numerical simulation verification. Because
cable minimum bending radius of Rmin, using the following formula: the numerical simulation software can clearly display the internal
In formula (6) Rmin unit is m, D is unit O.D., ～max is the unit max. components of the cable under load, the interaction between the
stress and strain components, so it can fully simulate the actual stress
of submarine cable. Tab 2 shows the design theory of physical and
mechanical properties of the flexible HVDC cable value and simulation
strain, and Rd is the distance between the center of the unit and cable. value. Thus, the agreement between them is very good, and the numerical
By calculation, the minimum bending radius of the flexible HVDC simulation values of the relevant tensile properties can meet the design
submarine cable is 2.535 m, which is meet the minimum bending radius requirements of tensile load, which also fully verifies the reliability of the
of the design requirements of flexible HVDC submarine cable. theoretical analysis.
Tab 2 Physics and mechanics of flexible HVDC submarine cable
3.6 Tensile bending performance design
In the process of flexible HVDC submarine cable using, load is the
most common combination of stretching and bending, so the bending
performance design is very important.The following theoretical
calculation formula is used to design the bending performance of the
flexible HVDC submarine cable

In formula (7) εt is the strain under tensile load, F is tensile force,
Kt,a is tensile stiffness, εb is bending strain, R is circle radius, α is
helix angle, ρ is the radius of curvature.
4. Process optimization of electrical performance
The loading capacity of the armored is determined by the ultimate In the process of development of the flexible DC cable, found that the
stress state, when (where σs is yield strength, μ is safety insulation production process has an important influence on its electrical
coefficient, σy is maximum equivalent stress), armored layer performance. In order to make the electrical performance of the flexible
capacity reached a critical state, the formula (7) can be changed into HVDC submarine cable is developed to meet the requirements, must
F and a equation: be insulated for the production of submarine conductivity, space charge
distribution and dielectric properties of the strict control. Thus, [1]
carried out in-depth research on the optimization of production process
of cable insulation
In formula (8) εy is the equivalent strain, and α is the helix angle.
Formula (8) can be abbreviated as:
4.1 Process optimization,test design and sample preparation
In the production of cable insulation optimization, choose different process
conditions (degassing process, crosslinking temperature and pressure)
formula (9) σax is axial stress, and f is a combination function of
curvature radius and tension. produced 5 pieces of flexible HVDC cable samples, as shown in Tab 3
Tab 3 Flexible HVDC cable samples with different process conditions of
The tension bending loads (bending performance) curve verification, trial
evaluation of the flexible HVDC cable bending performance. Figure 5
shows the installation work and corresponding when the armored yield
when the HVDC cable tension curve bending performance. Obviously,
the maximum tensile force of the flexible HVDC submarine cable is 472
kN, the minimum bending radius is 2.535 m, the maximum tensile force
of flexible work to meet the HVDC submarine cable and the minimum
bending radius of the design requirements
Figure 5 Performance curves of tension and bending during installation
and operation
installating
working
4.2 Analysis of test results of process optimization
4.2.1 Analysis of test results of insulation conductivity
In order to understand the different process conditions (degassing
process, crosslinking temperature and pressure) influence on the
conductivity of insulated flexible HVDC submarine cable, submarine
cable insulation of the 5 specimens were γ conductivity test, the test
results are shown in Figure 6, A. is not degassing: conductivity of sample
1 is minimum, which is result from t has more crosslinking by-products
46 minimum curvature radius