A complete set of information on submarine cables

According to incomplete statistics, the total length of China's coastline exceeds 18000 km and there are more than 5000 islands. From a worldwide perspective, the length and number of coastlines are larger and more. With the depletion of global petrochemical energy and the increase of human demand for electricity, human production activities gradually move towards the ocean, such as offshore wind turbine power generation, marine tidal energy, marine natural gas and oil exploitation, and there is only one way to obtain energy, that is submarine cable. In 2012, China's cable manufacturing scale surpassed that of the United States to become the world's first cable manufacturing country, but it must be clear that a considerable number of high-end products, such as XLPE insulated 500kV ultra-high voltage power cables and ultra-high voltage large cross-section submarine AC / DC power cables, mostly rely on imports. In September 2012, China wire and cable industry conference was held in Shanghai. At the conference, Dow Chemical, Nordic chemical, Portia, Germany and other material and equipment suppliers mentioned the most word is "submarine cable". At the Asian cable Summit Forum held in Shanghai on November 27, 2012, the most mentioned word by many cable manufacturers and supporting suppliers at home and abroad is "submarine cable". Therefore, we in the cable industry can't help asking - is the manufacturing spring of submarine cable in China coming? This paper briefly introduces the materials, equipment, executive standards, installation and laying details and precautions of submarine cables.

Current situation of submarine cable production at home and abroad

Submarine cables have been developed, produced and laid for nearly 170 years. In 1850, the first submarine cable in human history was laid between Britain and France; China's first submarine cable was completed in 1888. There are two cables, one between CHUANSHI island in Fuzhou and Huwei in Taiwan, and the other from Anping in Tainan to Penghu, which were organized and laid by Liu Mingchuan, then governor of Taiwan.

Submarine cables are divided into: impregnated paper wrapped insulated cables, oil filled cables and extruded cables (XLPE crosslinked polyethylene insulation and EPR ethylene propylene rubber insulation). Impregnated paper wrapped insulated and oil filled cables are basically eliminated due to the limitation of water depth and laying drop. At present, XLPE insulated cable is the most widely used.

According to the current transmission mode, submarine cables can be divided into AC transmission and DC transmission. At present, some large foreign cable enterprises, such as Italy Prius, Japan tengcang cable, Japan Guhe Co., Ltd., Japan Sumitomo electrician, France nexen, South Korea ls and American general cable, have the ability to continuously produce ultra-high voltage and large cross-section DC submarine cables, and have the soft joint technology of submarine cables, At the same time, it can provide an integrated solution for installation and laying; China's submarine cable is only in its infancy. At present, there are few domestic enterprises with submarine cable production capacity.

AC and DC extruded XLPE insulated submarine cables

As for the selection of AC and DC submarine cables, it is generally believed that DC submarine cables have less loss and transmit more power. The specific research on the relationship between AC and DC submarine cables and laying distance has not been reported in China. The Italian cable company Pressman presented the relationship between AC and DC submarine cables and laying distance at the Nordic chemical energy infrastructure seminar held in New York on October 4, 2011. 

Relationship between AC and DC cables and laying distance

As shown in the above figure, the ordinate is the voltage level and the abscissa is the cable laying length. It can be seen that when the submarine cable laying length exceeds 120km, presman's choice is DC cable, while when the submarine cable laying length is less than 110km, AC cable is the better choice. The most essential difference between DC and AC cables is the performance of insulating materials (mechanical and electrical properties, such as inhibiting space charge accumulation). Compared with AC cables, DC cables have longer length, longer degassing time, higher requirements for XLPE cleanliness, better scorching performance and longer continuous production time. At present, the cable materials (including conductor shielding, insulation shielding and insulation materials) of high-voltage and ultra-high-voltage XLPE insulated submarine cables produced by all cable manufacturers in the world are almost from Nordic chemical and Dow Chemical.

Comparison of current carrying capacity of XLPE insulated 500kV AC and DC cables

As shown in the figure, the abscissa is the nominal section of the conductor. The ordinate is the conductor current carrying capacity. The three lines in the quadrant are DC cable, steel wire armored AC cable and flat copper wire AC cable from top to bottom. It can be seen from the figure that DC cable has obvious advantages in current carrying capacity when the section of 500kV cable exceeds 1000mm2.

Brief introduction of single core and three core optical fiber composite submarine cable

Generally speaking, at present, the most widely used single core and three core optical fiber composite submarine cable is the structure shown in the figure below, that is, the circular compact stranded copper conductor is used for 800mm2 and below, and the split conductor structure (5 or 6) XLPE shielding and insulation are used for 1000mm2 and above. The optical fiber distribution is generally placed in the filling layer or steel wire armor, and the optical fiber in Figure 4 is placed in the filling layer.

XLPE insulation 220kv-1 × Structure diagram of 800mm2 optical fiber composite single core and three core submarine cable

At present, it is recognized in the industry that steel wire armor is preferred for single core and three core submarine cables for a variety of reasons, such as strong mechanical force will be applied during submarine cable laying, and good tensile performance is required. As for the selection of single core and three core cables in the same project, at the Asian cable Summit Forum held in Shanghai on November 27, 2012, a domestic cable enterprise made a comparative analysis in combination with the losses of conductor, metal shield and armor. See the following table for details:

Comparison and analysis of 220 kV Single core and three core submarine cables

Production, transportation and laying of submarine cables

The selection of insulating materials with excellent electrical performance also requires relevant equipment and convenient transportation channels, as shown in the production flow chart below. The equipment for producing submarine cables include: double head or multi head on-line annealing large puller, 120 coil (or more) 630 steel wire armouring machine, 150 lead pressing machine, 3 × 4500 or 3 × 10000 and above vertical cable forming machine, 200kV or 500kV catenary or vertical tower AC / AC line, etc; Generally, the production of submarine cables must be close to the river channel for convenient transportation. The required transportation equipment include: on-site circulation active turntable, yard turntable, transportation ship, etc.

Basic production process of submarine cable

Submarine cable laying is a huge and complex project, which mainly includes three stages: Cable Route Exploration and cleaning, submarine cable laying and buried protection. At present, almost all submarine cables produced by domestic cable manufacturers in China seek third-party laying. Looking at the world, the only cable enterprises that can produce and lay their own cables are presman, nexen, LS and other giants. Some enterprises have developed submarine cable laying robots for practical operation. Figure 6 shows the submarine cable laying ship and laying site. 

Submarine cable laying ship and installation site

The R & D, production, laying and maintenance of submarine cables abroad have formed standardized operations. The key technologies of submarine cables are the internal and external shielding and insulation of large-length submarine cables, flawless extrusion, combined cable forming, soft joint and optical fiber unit structure research (composite submarine cable). In recent years, China has vigorously developed offshore wind power and oil and gas projects, which requires a large number of submarine cables to transmit power and communication, which has injected a good prescription into the weak Chinese cable industry. The 2012 Seminar on deepwater oil and gas drilling and production equipment and technology in the South China Sea held in Beijing in November 2012 sent a message that it is urgent for China to develop marine resources. At present, China's domestic cable and supporting enterprises only occupy the link of design, processing and manufacturing in the submarine cable industry chain, while the cable materials and equipment in the upstream and the installation and laying in the downstream are monopolized by foreign countries such as Nordic chemical, trest and pressman. Here, the author suggests that powerful cable enterprises can try to participate in Nordic chemical Dow Chemical and other raw material suppliers (once Sino US relations deteriorate, the above two cable material enterprises will block the supply of raw materials, which will have a bad impact on China's high-voltage and ultra-high-voltage cable industry), learn from some enterprises to set up factories in joint venture or cooperation with foreign first-class cable enterprises, purchase or cultivate professional submarine cable installation teams. The nationalization of China's submarine cable industry chain still has a long way to go.