But what is outrageous is that Norway's submarine cables have frequently broken since last year, and once occurred in November 2021 and January 2022, and under natural conditions, the submarine cables are unlikely to be destroyed.

Following the mysterious leakage of the " Norwegian-1" and " Norwegian-2" pipelines that transport natural gas to Europe, the submarine cable of Norwegian- broke for unknown reasons.

is different from the natural gas transmission pipeline. Submarine cable not only plays the role of in transporting energy , but also an important channel for stabilizing communication services and financial network . But what is outrageous is that Norway's submarine cables have frequently broken since last year, and once occurred in November 2021 and January 2022, and under natural conditions, the submarine cables are unlikely to be destroyed.

submarine cable: What exactly does it do?

submarine cable is referred to as submarine cable , which refers to a cable laid inside or on the seabed , and the transmission medium is wrapped with dense insulating material . The specifications of submarine cables are thicker and thinner, and the cables in the deep sea are thinner (related to the environmental disturbance intensity). The common diameter of modern cables is 25mm and weighs about 1.4 tons per kilometer.

According to the function, submarine cables can be divided into power cable and communication cable . The former is mostly used for power transmission in projects such as offshore wind power , with a short laying distance, while the latter is used to connect communications to different countries and regions, with a range and length far exceeding power cables.

Since the laying of the first submarine cable of in the 1850s, the global cable construction scale and design concept have been continuously developed. The current cable is no longer limited to a single function. fiber -power composite cable can simultaneously realize the function of transmitting power and signals. It has both conductor and fiber .

It is estimated that submarine cables carry more than 95% of the world's data transmission and international voice, and its advantages are difficult to replace by other communication methods. Compared with traditional wireless telegraphs, submarine cables can achieve long-distance voice communication, which is more secure and less likely to be intercepted. Compared with satellite communication, the advantages of submarine cable communication are also clear at a glance: higher cost performance, larger communication capacity, and faster transmission speed. This is because the signal transmitted by the submarine cable is a beam rather than a current. The communication carrier is an optical fiber made of glass. The diameter of a single optical fiber is only 0.1mm, it is light in weight and soft in texture. Hundreds of optical fibers are bundled into optical cables, which increases the communication capacity. The beam is transmitted in a total reflection mode, with low loss, and can almost realize instantaneous communication .

In addition, submarine cable communication is not affected by electromagnetic interference , the transmission signal is stable, the reliability is high, and the raw material for making optical fibers ( quartz ) is also very cheap. With many advantages, the submarine cable project has naturally received attention from all countries. The construction scale has expanded rapidly since the 1990s. Now the world has built a complete submarine cable communication network.

Europe is one of the regions with the highest density and largest scale of submarine cable laying in the world. The complex submarine cable lines form the "underwater artery" of Internet data. Among them, Norway's submarine cable is an important puzzle for European network data, and the impact of the breakage accident cannot be underestimated!

submarine cable comes with its own three-layer "protective film"

submarine cable has an unparalleled status in the field of communications, and the laying environment determines that it is often impacted by submarine currents and friction from submarine materials. Therefore, the design of submarine cables is very particular and comes with a protective layer when they leave the factory.

Take the current mainstream fiber-power composite cable as an example, and its core parts are conductors and optical fibers. Among them, the conductor requires good conductivity and is generally made of copper or aluminum. In contrast, copper has better current carrying capacity than aluminum, and the use of copper conductors can also reduce the use of outer materials such as lead and steel wire.

But with the same transmission capacity, the cost of copper conductor cable is 1.1~1.8 times that of aluminum conductor cables, and the cost of copper material is more expensive. But even so, most manufacturers still choose copper as the power supply conductor, which shows that the quality of submarine cables is more important than economics.

When it comes to quality, the key is to look at three major protective layers: insulation-shielding layer , protective layer and armor layer .

1, insulation-shielding layer.The insulating materials include crosslinked polyethylene and ethylene propylene rubber . The former is the most widely used and the English abbreviation is XLPE. This material is high-grade polyethylene containing organic peroxide , which is more heat-resistant and corrosion-resistant than ordinary polyethylene .

In addition to the insulation layer, the conductor and optical fiber are also wrapped with shielding layers, such as conductor shielding and insulation shielding. According to the survey, most manufacturers use three-layer extrusion and dry crosslinking tubes to make crosslinked polyethylene cables, forming the " conductor shielding-insulation-insulation shielding " system for the conductor, forming a stable media interface, and the shielding effect is quite ideal.

2, protective layer. There are protective structures inside and outside the submarine cable, with metal lead sleeves and semiconductor PE jackets inside, which can protect metals from corrosion and wear. The inner sheath is mostly made of polyethylene, and some styles also add carbon black semiconducting polyethylene to produce polymer sheath. The protective structure of the outer layer of

also has a variety of material combinations, such as: rubber cotton tape, PP inner cushion layer, asphalt layer and PP outer cushion layer. Among them, the nominal thickness of the rubber cotton tape is 0.1 mm, the inner cushion layer is 2.0 mm, the asphalt layer is 0.5 mm, and the outer cushion layer is 4.0 mm. The outer layer has direct contact with seawater and has strong corrosion resistance. In order to facilitate underwater identification, the outer layer is generally marked with color.

3, armor layer. In addition to insulation and protective materials, armor is also a key component of submarine cables. The so-called armored is made of bronze, brass , copper or aluminum, and other metals twisted at a certain pitch according to the extension direction of the cable. The common ones are 1 to 2 layers. Therefore, the armor layer has a metallic structural strength, which can provide mechanical protection for submarine cables.

With these three layers of protection, the submarine cable can withstand the test of most submarine environments and its normal service life can reach 15 to 20 years. In addition to the wear and corrosion protection of the material itself, engineers also protect the cables by burying, trench, pipe penetration and covering . The mainstream burying protection is to bury the cables 2.5~3.0m deep in the seabed, minimizing the influence of natural factors.

Only in rare cases can the submarine cable be destroyed, such as shark bites, earthquakes, tsunamis and other disasters. However, the incidence of the above factors is very low and is not the main reason for cable damage.

Scientists have conducted statistics on submarine cable repair accidents in the Atlantic Ocean and Caribbean Sea. The results show that between 1959 and 1996, the proportion of natural failures in all cable accidents was less than 9%, and more than 90% of cable accidents were related to human activities.

human factors that cause cable failure are more common in trawler operations and ships break down . Of course, it is not ruled out that someone deliberately destroys it. What is really difficult is that the undersea cable laying environment is hidden and there is a lack of evidence of underwater monitoring. Once it is damaged, it will be difficult to repair and it will be difficult to find out the culprit.

submarine cable has a fault. How difficult is it to repair?

The maintenance of submarine cables is one of the biggest difficulties in marine engineering. Compared with onshore cables, the maintenance time of submarine cables is more urgent, the construction risk is high, and it is significantly affected by the weather and depth of the sea area, and the maintenance cost is dozens to hundreds of times higher.

The first step in submarine cable repair is to find the breaking point. For fault location, the multimeter and megohmmeter are generally used to detect the ground insulation resistance and phase-to-phase resistance of the fault cable, and initially determine the nature of the fault. Then use optical time domain reflector (OTDR) or spread spectrum time domain reflector (SSTDR) to measure the fault points, and initially infer the relative distance between the break point and the platform or land.

The second step is to send the repair ship to the fault prediction point, anchor in place, and place a marking float near the breakpoint. The key procedure is to use grab with rigid pointed tips to drag and pull back and forth on the seabed, "rake-style" salvage cables. Then tie the faulty cable with a float to get out of water, and use the same method to remove the cable at the other end, and connect the cables at both ends on the deck.

The next process is roughly the same as the maintenance of land cables: cut off the fault point, perform DC resistance measurement of conductors, insulation measurement, voltage withstand test , and then connect the connector after confirming that there is no fault.

The last step is to check the connected submarine cable to ensure insulation performance and communication quality. According to the maintenance requirements, the length of the access submarine cable is longer than the original fault submarine cable, and finally laid in the seabed in a U-shaped shape.

Norway has obviously accumulated rich experience in cable maintenance. In addition, the break point is close to the platform and the seawater depth is suitable. It is expected to be repaired in a few days to a week. As for the truth about the accident investigation, I believe the truth will be revealed, and we will wait and see.