Based on the large demand of medium and low voltage Cable Manufactor in China, the manufacturing level and equipment level of cable industry, the new product technology and the gap with the international advanced level, the following suggestions are put forward for the follow-up development:
One is the standard of medium and low voltage power cables. In combination with the implementation of IEC standards, technical requirements of low and medium voltage power cables at the user end and the need of entering the international market in China, a high-quality medium and low voltage power cable product and accessories standard system with Chinese characteristics is established, including product standards, material standards, laying and installation of various application scenarios used in the standard type, and operation and maintenance specifications.
Second, the material of medium and low voltage power cable. At present, XLPE insulation is widely used (and some low voltage power cables use PVC insulation). It should be affirmed that XLPE material is a very mature technology and indispensable nowadays. Based on the environmental protection, manufacturing process optimization and product performance improvement, the research, development and application process of new materials, including thermoplastic PP elastomer materials, etc., should be accelerated.
Third, we will eliminate backward equipment in an orderly manner and promote transformation and upgrading. Based on the fact that the current industry capacity of medium and low voltage aac cables is too excess, advanced and backward production equipment coexists, and the quality of crystal production is uneven, it is suggested that the evaluation standards should be formulated through the third-party professional institutions, and the production equipment with low efficiency, high energy consumption, unstable quality, high operation and maintenance cost and environmental impact should be eliminated in an orderly manner, and the transformation and upgrading should be encouraged, Encourage the application of high-performance production equipment, digital and information technology and advanced detection technology.
Fourth, enterprises producing medium and low voltage power cables should strengthen management innovation. Improve lean management, guide agglomeration and scale, constantly adopt new processes and materials, improve product price performance, meet customer demand with high-quality products and services, and promote the improvement of industry manufacturing level.
3.66kv-500kv power cable
(1) market demand
The power cables with rated voltage of 66kV and above belong to the range of high voltage and ultra-high voltage cables in China. According to the different system voltage, it can be divided into 66kV, 110KV, 220kV, 330kV and 500kV, among which 220kV and above voltage class belongs to UHV cable. According to the voltage type, it can be divided into two types: AC cable and DC cable. According to the insulation type, it can be divided into XLPE and oil immersed paper insulated cable (including oil filled cable), which has been rarely used in China, only about 100 km of the line in operation. According to the application scenario, it can also be divided into onshore cable and submarine cable. At present, the power cable with Extruded Crosslinked polyethylene insulation is widely used.
The structure of XLPE insulated high-voltage cable is usually relatively fixed, mainly single core cable, including conductor, conductor shield, XLPE insulation, insulation shield, semi-conductive buffer layer, wrinkled aluminum sheath and non-metallic outer sheath. The typical cable structure is shown in Figure 2-5.
High voltage power cable is mainly used in power transmission system, including the transmission to the large load center, the new energy base (wind power, photovoltaic, etc.), and long-distance island power supply. The main users are national grid, southern power grid, power generation groups and large-scale industrial and mining enterprises.
By the end of 2018, the power cables of 66kV and above of the national grid have 14595 lines, with a length of 27874km, with an annual growth of about 12%. In addition, with the rapid development of offshore wind power in China, the demand for high voltage cables (especially submarine cables) is in a “blowout” state, and the annual demand for 66kV and above high-voltage submarine cables exceeds 2000 km.
The annual consumption of high voltage and UHV power cables is about 15000km.
(2) capacity of existing equipment
The equipment of power cable with rated voltage of 66-500kv includes conductor stranding equipment, three-layer insulation extrusion equipment (vertical cross-linking production line VCV, high performance catenary production line hccv), wrapping machine, aluminum press or welding wrinkled aluminum sleeve production line and sheath extruder.
The investment in production equipment is large, and the key equipment is vertical cross-linked production line VCV and high performance catenary production line hccv. The capacity of the equipment determines the capacity of high voltage power cable. The annual capacity of each VCV production line is usually 300km and that of hccv is about 400km.
According to the equipment of more than 100 VCV production lines in China, the annual capacity of power cable with rated voltage of 66-500kv has exceeded 40000km. In addition, the capacity of hccv production line has fully met the market demand and there is still considerable overcapacity.
(3) technical innovation and existing problems
The technology of high voltage power cable in China mainly comes from mature technologies in developed countries such as Europe and Japan. The scenario adaptability of high voltage cable application is particularly important. In the high voltage cable products, the depth and breadth of technical innovation in China are not enough.
At present, the technical innovation that has been applied in high voltage cables mainly focuses on the outer layer of cable, such as non-metallic outer sheath, including flame-retardant outer sheath, double outer sheath with extruded semi conducting and termite proof sheath.
There is no significant technological innovation on the internal structure of cable and raw materials. The main raw materials and production equipment are imported. According to the application practice over the years, for the power cable with rated voltage of 66-500kv, the following problems still exist in technical innovation at present:
First, the insulation materials and semi conducting shielding materials mainly rely on import, including the insulation and shielding materials for AC and DC cables, especially the ultra purified insulation materials and super smooth shielding materials. Although domestic material enterprises have developed, they have not yet fully localized;
Second, the evaluation of the quality and operation status of high voltage cable is not systematic, and it can not fully reflect the operation life of high voltage cable in various scenarios;
Third, all key production equipment rely on import, such as: vertical cross-linking production line (VCV) and catenary cross-linking production line (hccv) equipment, and domestic equipment manufacturers have not invested enough to realize localization;
Fourth, the structure of the semi conducting buffer water barrier of high voltage cable has not been fully verified for its long-term applicability and structural reliability;
The fifth is that the metal sheath structure is basically wrinkled aluminum sheath, and the research on the gap design and process cooperation of buffer layer is not enough;
Sixth, the conductor structure is basically a tight pressed circular stranded conductor or split conductor, and the research on improving the current distribution of large section conductor is not enough;
The technology of accessories for UHV (500kV) is not mature.
The reasons for the above problems are many aspects. Besides the late start of high voltage cable in China, the application and basic research are weak, it is also related to the power operation system in China. The power system in China has been centralized management for a long time, integrated management of transmission and distribution and operation and maintenance. On the one hand, it ensures the overall reliability of power supply, but there is also a single design and line engineering model. The application of personalized research and new technology for application scenarios is relatively slow, which makes the upstream industry innovation insufficient.
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