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Fiber Optic Sensor to Monitor Strain and Temperature Within Cables

In an article published in the journal Sensors, researchers demonstrated that by the judicious placement of a fiber-optic sensor (FOS), strain and temperature within copper cables submitted to bending could be monitored.

fiber optics, copper cables

Study: Fiber-Optic Sensors (FOS) for Smart High Voltage Composite Cables—Numerical Simulation of Multi-Parameter Bending Effects Generated by Irregular Seabed Topography. Image Credit: TakaYIB/Shutterstock.com

Need for High-Voltage Electrical Transport Cables

Reaching carbon neutrality may be accomplished in several ways, one of which is developing dependable renewable energy sources, such as wind energy generated offshore.

The International Energy Agency (IEA) predicts that offshore wind energy will be listed as the top power source in Europe within two decades. Large-scale development of renewable energy sources and related technologies is required for a carbon-neutral economy, necessitating infrastructure expansion and upgrades. As a result, recent years have seen a significant increase in the focus placed on studies concerning offshore energy infrastructure, particularly with large-scale wind blades and high-voltage electrical transport cables.

Shutdowns and their Effects

High-voltage cables may have an upfront performance loss during shipping, handling, and embedding in seabeds. This may increase usage restrictions in hostile media, such as seas, and early shutdown risks. Shutdown results in high fiscal losses and generates major challenges, which might have catastrophic implications.

In addition to the costs associated with their operation and maintenance, offshore cables are susceptible to failures, which account for eighty percent of the total financial losses and insurance claims. In the previous seven years, more than 90 offshore cable failures have been documented, resulting in over 350 million dollars worth of insurance claims.

The Decline in Cable Effectiveness

The plastic deformation of copper, which may occur under relatively light loads and directly influence other physical qualities, is mostly to blame for the decline in cable effectiveness. This demonstrates that monitoring what occurs within high-voltage cables used for offshore farms in real-time and with high precision is necessary. This can be accomplished by inserting sensors of various types in the area surrounding the cables. These sensors help monitor the levels of deformation and temperature of the copper while it is in service. One example of such sensors is fiber-optic sensors (FOS).

Embedding FOS in Copper Wires

A method that involves putting FOS in between copper wires or inside the insulator XLPE (cross-linked polyethylene) is presented in this study. Phase monitoring and fine bending are the primary focuses of the placement method. A numerical simulation analysis is also presented as part of the projected work, which may assist other engineers in locating the most appropriate and cost-effective solutions.

Properties of XPLE and Copper

A single phase of the Nexans submarine power cable rated at 35 kilovolts is taken into consideration in this model. Because of its excellent performance both at various temperatures, XPLE is best for use in high-voltage electric cables. The Young's modulus of XPLE has been shown to decrease with increasing temperature, in contrast to the material's thermal expansion, which exhibits the opposite tendency. Copper expands by less than 3% over the same temperature range, but the thermal expansion coefficient goes up by 5% over the same temperature range of 25 to 105 degrees Celsius.

Conclusion

Incorporating FOS as a kind of structural health monitoring (SHM) inside a high-voltage phase of a smart electric cable designed for offshore use is an effective and dependable method for continually monitoring critical structures. The key advantage of this method is remote monitoring. This idea was first presented in an earlier investigation of the tensile loading of the smart energy transport cable in another research. However, this study focused on crucial bending characteristics, which are particularly important when considering the topography of steep sea beds.

Under bending, which may mimic the uneven topography of sea bottoms, the multi-axial strains value of copper and FOS wires were compared. The best results were obtained by placing FOS in a straight line parallel to the main copper wire. Engineering problems involving significant FOS-copper friction may lead to sensor failure without appropriate FOS-coating technologies. The embedding of FOS at a distance of 1mm within the XLPE is another location that exhibits promising outcomes.

Future Prospects

This study did not address the specific situation of a cable that bends on sloppy seabeds. Instead, the purpose of the study was to provide a model for the use of embedded fiber-optic sensors and to consider all the research that needs to be done to further recommend this technology to cable makers. The numerical model can visualize numerous embedded FOS situations and related monitoring scenarios, aiding engineers in future cable design.

Reference

Monssef Drissi-Habti, Abhijit Neginhal, Sriharsha Manepalli and Valter Carvelli (2022) Fiber-Optic Sensors (FOS) for Smart High Voltage Composite Cables—Numerical Simulation of Multi-Parameter Bending Effects Generated by Irregular Seabed Topography. Sensors. https://www.mdpi.com/1424-8220/22/20/7899

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

Taha Khan

Written by

Taha Khan

Taha graduated from HITEC University Taxila with a Bachelors in Mechanical Engineering. During his studies, he worked on several research projects related to Mechanics of Materials, Machine Design, Heat and Mass Transfer, and Robotics. After graduating, Taha worked as a Research Executive for 2 years at an IT company (Immentia). He has also worked as a freelance content creator at Lancerhop. In the meantime, Taha did his NEBOSH IGC certification and expanded his career opportunities.  

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