Cables are essential for linking remote and offshore energy sources to the grid. Offshore wind farms are generally constructed because the wind speed at sea is in most cases higher than on land, which results in a large increase in energy production. Offshore wind speeds also tend to be more stable than on land, and a more stable wind input provides a more productive source of energy. There are a lot of big cities right on the water. Obviously, they require a great deal of energy. Building offshore wind farms is a surefire way to supply nearby cities with the electricity they need. This article will examine their importance and the engineering challenges encountered during their installation.
Comparison with overhead transmission lines
Submarine and underground electrical wiring offer advantages over traditional overhead lines. To transmit and distribute electricity, an overhead line uses bare conductors held aloft by a pole or tower. An insulated cable that runs beneath the ground for the purpose of distributing and transmitting electricity is known as an underground cable. Overhead lines employ a smaller diameter of conductor whereas cables run underground need a substantially larger conductor. The voltage rating of overhead lines is around 765 kV, which is greater. The voltage rating of underground wires is somewhat lower. The standard limit is 66 kV.
Overhead lines have a higher carrying capacity at the moment. The capacity to transport current is lower for underground wires. Insulation needs to be reduced for overhead lines. Insulation is unnecessary for overhead lines. In most cases, this occurs at the support's points of contact. It is necessary to insulate underground cables more. The reason behind this is that the insulating layer must cover the entire conductor. Moreover, communication lines in the area may be disrupted by overhead lines but being buried beneath the Earth's surface, underground cables do not disrupt communication lines. When distributing and transmitting electricity across long distances, overhead lines are utilized. Transmission and distribution of power over short to medium distances is accomplished through the use of underground cables.
Engineering challenges
Installing cables underground or in the water is an extremely difficult engineering project. When laying cables underground, it's important to think about the soil type, where utilities are located and how important it is to maintain surface work as unbroken as feasible. Underwater cable installation is already a complex procedure, but laying the cables exactly on the seabed — which often involves very deep water — needs specialized vessels and methods. The cables must be robust enough to resist the corrosion, strong currents, and possible damage from fishing gear that is common in severe seas.
The underground wires may also be more difficult to inspect and maintain on a regular basis than the lines above ground, necessitating new methods and equipment. Insulation degradation, poor heat dissipation, ground movement, water penetration and unseen physical damage during installation all contribute to underground cables having a shorter lifespan compared to overhead lines. Many offshore wind farms are located hundreds of kilometers or even tens of kilometers away from the onshore grid. So, HVDC technology, which is superior to AC systems for long-distance power transmission, must be used.
Techniques being used to address engineering challenges
1. Trenchless technologies:
- Horizontal directional drilling (HDD): This technique involves drilling a narrow bore beneath the surface, allowing the cable to be pulled through without extensive excavation. This minimizes disruption to the environment and existing infrastructure.
- Pipe jacking: This method involves creating a tunnel beneath the surface using hydraulic jacks, through which the cable is then inserted. It is particularly useful in urban areas with limited space for open trenching.
2. Advanced cable design:
- High-temperature superconducting (HTS) cables: These cables operate at extremely low temperatures, enabling them to carry significantly more power with minimal energy loss. They are cooled down to extremely low temperatures using liquid nitrogen or liquid helium to activate the superconductivity phenomenon and operate at near-zero resistance. This is particularly beneficial for long-distance transmission and reduces the need for large, bulky cables.
- Extruded dielectric cables: These cables use a solid dielectric material instead of oil, reducing the risk of leaks and environmental contamination. They also have a smaller footprint and are easier to install.
3. Submarine cable installation techniques:
- Dynamic cable laying: This method involves laying the cable directly from a specialized cable-laying vessel, allowing for precise placement on the seabed even in deep water. A specialized cable-laying vessel is a deep-sea-going ship specifically designed and equipped to lay underwater cables on the ocean floor.
- Ploughing: This technique involves using a plough to bury the cable beneath the seabed, protecting it from fishing gear and other potential damage. A plough is a specialized piece of equipment towed behind a cable-laying vessel. It's designed to create a trench in the seabed as it moves, burying the cable beneath the surface.
4. Monitoring and maintenance:
- Fiber optic sensors: These sensors are embedded within the cable and can monitor its condition in real time, allowing for early detection of faults and potential problems. For instance, Fiber Bragg Grating (FBG) sensors are embedded within the fiber optic cable and respond to specific environmental conditions like temperature, strain and pressure
- Remotely operated vehicles (ROVs): These underwater robots can be used to inspect and repair cables, reducing the need for expensive and time-consuming diving operations.
Conclusion
To ensure that the produced clean energy reaches customers and contributes to a sustainable energy future, submarine and underground cables are essential for transmitting the generated electricity over vast distances. The installation of submarine cables is significantly challenging, necessitating specialized vessels and methods to precisely lay the cables on the seabed, frequently in extremely deep water. Strong currents, corrosion and the possibility of damage from fishing gear are all elements that these cables must be able to endure in the hostile marine environment.
