Concept of Placement of Fiber-Optic Sensor in Smart Energy Transport Cable under Tensile Loading

Abstract

Due to the exponential growth in offshore renewable energies and structures such as floating offshore wind turbines and wave power converters, the research and engineering in this field is experiencing exceptional development. This emergence of offshore renewable energy requires power cables which are usually made up of copper to transport this energy ashore. These power cables are critical structures that must withstand harsh environmental conditions, handling, and shipping, at high seas which can cause copper wires to deform well above the limit of proportionality and consequently break. Copper, being an excellent electric conductor, has, however, very weak mechanical properties. If plasticity propagates inside copper not only will the mechanical properties be affected, but the electrical properties are also disrupted. Constantly monitoring such large-scale structures can be carried out by providing continuous strain using fiber-optic sensors (FOSs). The embedding of optical fibers within the cables (not within the phase) is practiced. Nevertheless, these optical fibers are first introduced into a cylinder of larger diameter than the optical fiber before this same fiber is embedded within the insulator surrounding the phases. Therefore, this type of embedding can in no way give a precise idea of the true deformation of the copper wires inside the phase. In this article, a set of numerical simulations are carried-out on a single phase (we are not yet working on the whole cable) with the aim of conceptualizing the placement of FOSs that will monitor strain and temperature within the conductor. It is well known that copper wire must never exceed temperatures above 90 °C, as this will result in shutdown of the whole system and therefore result in heavy maintenance, which would be a real catastrophe, economically speaking. This research explores the option of embedding sensors in several areas of the phase and how this can enable obtaining strain values that are representative of what really is happening in the conductor. It is, therefore, the primary objective of the current preliminary model to try to prove that the principle of embedding sensors in between copper wires can be envisaged, in particular to obtain an accurate idea about strain tensor of helical ones (multi-parameter strain sensing). The challenge is to ensure that they are not plastically deformed and hence able to transport electricity without exceeding or even becoming closer to 90 °C (fear of shutdown). The research solely focuses on mechanical aspects of the sensors. There are certainly some others, pertaining to sensors physics, instrumentation, and engineering, that are of prime importance, too. The upstream strategy of this research is to come up with a general concept that can be refined later by including, step by step, all the aspects listed above.

Fiber-Optic Sensors (FOS) for Smart High Voltage Composite Cables—Numerical Simulation of Multi-Parameter Bending Effects Generated by Irregular Seabed Topography

“…The locations chosen for FOS-sensor embedding in the phase (middle, helical-wound around the wires or even in XPLE, at various distances from the conductor) have been discussed in detail elsewhere [ 1 ]. Test configurations that were considered were FOS linear placement along the wires and/or within XPLE, and helical-wound around copper wires.…”

“…In the model that is suggested, a single phase of the 35kV Nexans submarine power cable is considered ( Figure 2 and Figure 3 , Table 1 ), 2XS2YRAA 18/30(36) kV [ 1 ] . Owing to its high- and low-temperature performance, XPLE is recommended for high-voltage electric cables [ 26 ].…”

“…Bending loading is considered applied on the bottom face of the submarine cable as shown in the Figure 4 . As detailed in a previous article [ 1 ], the same assumptions have been considered, i.e., the bending loading is applied along the lateral axis of the submarine cable with a magnitude of 80 MPa (it is assumed that the cable is submitted to hydrostatic pressure at a depth of 8000 m), and both the axial ends of the submarine cable are constrained with all the degrees of freedom fixed.…”

“…Indeed, it is clear that the carbon neutrality economy needs renewable energy sources and associated technologies to be developed at a huge scale, which imposes passes through upgrading and large development of infrastructures (both existing and new ones). A lot of research has been devoted to offshore energy structures in recent years, especially on large-dimension wind blades and high-voltage electrical transport cables [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]. The world is changing, and so are its energy needs.…”

“…In a previous article [ 1 ], structural health monitoring (SHM) using the optimal placement of FOS sensors inside a cable phase was proposed and demonstrated promising results, in the case where the cables are stressed in tension. In this new prospective article, numerical simulations were carried out in order to conceptualize the placement of FOS this time under bending stress.…”