Submarine cables are wires wrapped with insulating materials and laid on the seabed for telecommunication transmission. Submarine cables are divided into submarine communication cables and submarine power cables. Modern submarine cables all use optical fiber as the material for transmitting telephone and Internet signals. 1850 The world's first submarine cable was laid between Britain and France. The first submarine cable in China was built in 1888.

brief introduction

Submarine cable is a conductor wrapped in insulating material, which is laid under the seabed and rivers for telecommunication transmission. Modern submarine cables all use optical fiber as the material for transmitting telephone and Internet signals. 1850 The world's first submarine cable was laid between Britain and France. The first submarine cable in China was completed at 1888. There are two cables, one is between Ishikawa Island in Fuzhou and Huwei (Danshui) in Taiwan Province Province, with a length of 177 nautical miles, and the other is from Anping to Penghu in Tainan, with a length of 53 nautical miles.

classify

Submarine cables are divided into submarine communication cables and submarine power cables. Submarine communication cables are mainly used for communication services. Laying submarine cables is expensive, but it is highly confidential. Submarine power cable is mainly used to transmit high-power electric energy underwater, which has the same function as underground power cable, but its application occasions and laying methods are different. Because the submarine cable project is recognized by all countries in the world as a complex and difficult large-scale project, and the complex technology is applied to environmental exploration, marine physical investigation and cable design, manufacture and installation, there are only a few submarine cable manufacturers in the world, mainly Norway, Denmark, Japan, Canada, the United States, Britain, France, Italy and other countries, which provide laying technology in addition to manufacturing. At present, the domestic manufacturers that can produce submarine power cables are Shenyang Cable Factory and Shanghai Cable Factory. At present, the submarine power cables used in China still need to be imported.

use

Submarine communication cables are mainly used in long-distance communication networks, long-distance islands, cross-sea military facilities and other important occasions. The laying distance of submarine power cable is much shorter than that of communication cable, which is mainly used for land islands, crossing rivers or harbors, connecting drilling platforms or interconnecting drilling platforms from land. In general, the use of submarine cables to transmit electric energy is undoubtedly more expensive than overhead cables with the same length, but it is often more economical than using small isolated power stations for regional power generation and more profitable in offshore areas. This kind of cable is widely used in countries with many islands and rivers.

Ethnicity

1858, people laid the world's first submarine cable between North America and Europe. 1866, Britain laid a submarine cable connecting Britain and the United States in the Atlantic Ocean. Compared with land cables, submarine cables have many advantages: first, they don't need to dig tunnels or support with supports, so the investment is low and the construction speed is fast; Second, except for the landing area, most cables are at the bottom of the sea under certain test, and are not damaged by natural environment such as wind and waves and interfered by human production activities. Therefore, the cable is safe and stable, with strong anti-interference ability and good confidentiality. 1876, after Bell invented the telephone, new contents were added to submarine cables, and the pace of laying submarine cables on a large scale in various countries accelerated. 1902 global submarine communication cable completed. 1906, the world's first laser came out, and people began to use the characteristics of laser transmission in optical fiber to transmit information. 32 countries and regions in the world have established the most modern global communication network through submarine optical cables, which can carry out 300,000 telephone calls or data transmission at the same time. Submarine optical cable is also developing rapidly in China. 1993 The Sino-Japanese submarine optical cable system can open 7560 telephone circuits. 1997, Shanghai Nanhui built a world-class optical cable (flag), connecting 20 countries around the world, and can open120,000 telephone circuits. Now China has started to build two optical cables, China-US and Asia-Europe, and the total communication capacity will soar to 654.38+0.32 million.

Type and scope of application

Impregnated paper-wrapped cable-suitable for lines with AC less than 45kV and DC less than 400kV, and submarine cable can only be installed in water with water depth less than 500m; Independent oil-filled cable-suitable for DC or AC lines up to 750kV. Because the cable is oil-filled, it can be laid in the sea with a water depth of 500m without any difficulty; Extruded insulated (XLPE insulated, EPDM insulated) cable-suitable for AC voltage up to 200 kV. Compared with polyethylene, ethylene propylene rubber can prevent branching and local leakage, and make submarine cables play a more effective role; "Oil pressure" pipeline cable-only suitable for several kilometers long cable system, because it is mechanically limited to pulling extremely long cables into the pipeline; Inflatable (pressure-assisted) cables-Inflatable cables wrapped in impregnated paper are more suitable for long submarine cable networks than oil-filled cables. However, it is difficult to design cables and their accessories because of the need to operate under high pressure in deep water, which is usually limited to 300 meters.

manufacturing process

The whole manufacturing process of submarine power cables is basically the same as that of general power cables, but there are some special requirements for the mechanical strength and corrosion protection of cables, which require the cable length to be extended as much as possible. The manufacturing process of impregnated paper cable and extruded insulated cable is briefly described as follows. Impregnated paper cable is wrapped with insulating paper first, then vacuum-dried, oil-soaked, and then lead sheathed after conductor core is completed. At this time, you must keep squeezing. The extrusion of extremely long cable core is an extremely important step, which must be carried out day and night. The core of the oil-filled cable passes from the storage tank to the lead press through the siphon conveying pipe, and the degassed oil is injected into the pipe and flows to the core in the opposite direction to isolate the contact between the core and the air. After the wire core is wrapped with lead sheath, it needs to be coiled on the rotating platform (if it is an oil-filled or inflatable cable, a proper amount of metal reinforcing material can be added separately), then the cable is wrapped with polyethylene sheath (extrusion of polyethylene sheath is also a continuous operation), and finally two layers of galvanized steel wire armor are wrapped and coated with oil and hemp for impregnation. In the final production process, lead sheath and metal belt must be grounded through polyethylene sheath at an appropriate stage. The production process of cross-linked polyethylene cable and ethylene propylene rubber insulated submarine cable is similar to that of paper insulated lead sheathed cable except for extrusion vulcanization of synthetic rubber insulation layer, but lead sheath is not used.

Structural development

From 65438 to 0988, the transoceanic submarine optical cable (TAT-8) system was laid between the United States, Britain and France, with a total length of 6,700 kilometers. This cable contains three pairs of optical fibers, each pair of optical fibers has a transmission rate of 280 MB/s, and the relay station is 67 kilometers away. This is the first communication submarine optical cable across the Atlantic Ocean, marking the arrival of the era of submarine optical cable. 1989, the submarine cable across the Pacific Ocean (full length 13200 km) was also successfully built. Since then, submarine cables have replaced coaxial cables in the field of transoceanic intercontinental submarine cables, and submarine cables are no longer laid between oceans and continents. Optical fiber has large transmission capacity and long distance between relay stations, which is suitable for long-distance communication on the seabed. The optical fiber used in submarine cable is more demanding than that used in terrestrial cable; It requires low loss, high strength, long manufacturing length and long relay distance of optical fiber, generally more than 50 kilometers, and the transmission performance of optical fiber will not change within 25 years. In terms of the structure of submarine optical cable, it is required to withstand strong pressure and tension, especially deep-sea optical cable (optical cable laid on the seabed with water depth exceeding 1000m). In addition to the weight of the optical cable itself, the dynamic stress exerted by the waves on the optical cable should be added during the laying and maintenance. Under such a large load, the strain of optical cable should be limited to 0.7 ~ 0.8%. The structure of submarine optical cable requires firmness and light material, but light metal aluminum cannot be used, because aluminum and seawater will undergo electrochemical reaction to produce hydrogen, and hydrogen molecules will diffuse into the glass material of optical fiber, increasing the loss of optical fiber. Therefore, the submarine optical cable should not only prevent hydrogen from being generated internally, but also prevent hydrogen from infiltrating into the optical cable from the outside. Therefore, in the early 1990s, carbon-coated or titanium-coated optical fibers were developed, which can prevent hydrogen permeation and chemical corrosion. The optical fiber joint also requires high strength, and it is required to keep the strength of the original optical fiber and the surface of the original optical fiber from being damaged. According to the above requirements and characteristics, the basic structure of submarine optical cable is to spirally wind the optical fiber that has been coated once or twice in the center and strengthen the component (made of steel wire). Several typical structures of deep-sea optical cable: deep-sea optical cable, in which the optical fiber is sheathed in a spiral U-shaped groove plastic skeleton, and the groove is filled with ointment or elastic plastic body to form the fiber core. The fiber core is wrapped with high strength steel wire. In the winding process, all gaps should be filled with waterproof materials, and then a layer of copper tape is wound on the steel wire and welded, so that the steel wire and copper tube form a combination of compression and tension. This copper tube is also a conductor for transmitting the current of remote power supply. Steel wire and copper tube should be sheathed with polyethylene. This compact multi-layer structure is to protect the optical fiber, prevent the optical fiber from breaking, prevent the seawater from invading, and at the same time bear great tension and pressure when laying and restoring. Even with such strict protection, in the late 1980 s, there were cases where the polyethylene insulator of deep-sea optical cable was bitten by a shark and caused power failure. The remote power supply of submarine cable system is very important, and the repeaters along the submarine cable depend on the remote power supply of the landing office. The digital repeater used in submarine optical cable has many functions, which is several times larger than the analog repeater of submarine optical cable. Power supply requires high reliability and cannot be interrupted. Therefore, in shark infested areas, two layers of steel belts and one layer of polyethylene sheath should be added outside the submarine optical cable. In 1990s, submarine optical cable and satellite communication have become the main means of contemporary intercontinental communication. China participated in the construction and investment of 18 international submarine optical cable from 1989 to the end of 1998. The first international submarine optical cable system to land in China was1Sino-Japanese (C-J) submarine optical cable system built in February 1993. 1996 In February, the submarine optical cable between China and South Korea was completed and opened, landing in Qingdao, China and Taian, South Korea respectively, with a total length of 549 kilometers; 1997165438+1October, China participated in the construction of the submarine optical cable system (FLAG), which is the first intercontinental optical cable system to land in China, and has landed in Britain, Egypt, India, Thailand, Japan and other countries and regions 12, with a total length of 27,000. The Asia-Europe submarine optical cable system extension project initiated by China Telecom and Singapore Telecom is under construction. The system connects Asia, Europe and Oceania, and has landed in 33 countries and regions with a total length of 38,000 kilometers. It is the longest submarine optical cable in the world. Advanced 8-wavelength wavelength division multiplexing technology is adopted, and the design capacity of trunk route is as high as 40 Gb/s, landing in China, Shanghai and Shantou, 65438. The business volume of intercontinental communication undertaken by submarine optical cable has increased year by year, which has surpassed the business volume of satellite communication and become the main force of modern intercontinental communication.

Performance indicators and inspection methods

Mainly electrical performance indicators and mechanical and physical performance indicators. These indexes and inspection methods are the same as those of power cables with underground submarine cable structure. Electrical performance index: DC resistance and AC impedance of conductor; Insulation resistance of insulation layer; Dielectric loss; Current carrying capacity; Capacitance and inductance of cable; Induced voltage and current of metal sheath. Mechanical and physical performance index: mechanical strength of cable; Tensile strength and elongation of conductor; Mechanical and physical properties of insulating layer materials, etc. Inspection method: China mainly adopts the standards recommended by IEC, including IEC60502, IEC540, IEC 60/KOOC-0/4/KOOC-0/-KOOC-0/~ IEC 60/KOOC-0/-4, etc. Most cable manufacturers in the world have their own standards, mainly JIS in Japan, BS in Britain and CSA in Canada.

Because submarine cables want to be made longer to reduce the number of joints, it is best to produce them along the coast. Its packaging should be different from other cables. Usually, cables are wound on cable storage reels or turntables for transportation to cable laying ships, which transport cables to laying areas. Cable laying ship is specially designed and built for laying cables. The ship must also be equipped with facilities such as gantry crane, cable winch and oil injection system, but other ships equipped with additional mechanical equipment specially used for laying cables can also be used.