Study on Crosslinkable insulating materials for th

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Research on Crosslinkable insulating materials for high-voltage cables

power cables are an important part of the wire and cable industry. In the field of power cables: 1 ~ 10kV belongs to low-voltage cables, 10 ~ 35kV belongs to medium voltage cables, 110 ~ 220 makes the air in the studio unable to circulate fully, kV belongs to high-voltage cables, and 500kV belongs to ultra-high voltage cables

foreign countries began to produce high-voltage cross-linked polyethylene power cables in the 1970s. At present, foreign ultra-high voltage cross-linked polyethylene insulated plastic and ultra-high voltage cross-linked polyethylene insulated cables can reach the withstand voltage level of more than 500kV. Foreign UHV polyethylene insulated cables have been very mature and have established a complete system from polyethylene based materials, high-voltage cross-linked polyethylene insulating plastics to high-voltage cross-linked polyethylene cables

China's wire and cable industry started relatively late, but developed rapidly. After more than 17 years of accumulation and development since it was officially made in 1991, China's high-voltage power cable manufacturing has been quite mature, except for the ultra-high voltage grade. The domestic high-voltage cross-linked cable has established a perfect evaluation system, and the actual operation of more than 17 years has proved that China's high-voltage power cable has high stability

according to the current cable market situation in China and the development trend of industry demand, the top priority is to improve the scientific and technological content of cables, improve the technical level, and realize the high-end product structure. High voltage cross-linked cables of 110kV and above are urgently needed varieties of wires and cables in China at present

in addition, some major changes will take place in the national energy policy during the Eleventh Five Year Plan period. Reasonably solving the imbalance of national power resources and reducing the overall cable operation cost will become one of the themes of the eleventh five year plan. Especially after the financial storm, the infrastructure construction in the government's plan to stimulate domestic demand may be advanced. These changes will bring great development opportunities to China's high-voltage cross-linked power cables

on the premise of production equipment, market and opportunities, vigorously developing domestic high-voltage cable varieties has the following significance:

1. Change the current situation that China's low-end low profit products are rich, processed into cathode materials that can be sold for more than 100000 yuan per ton, and the lack of medium and high-grade products

2. Complete the upgrading of domestic cables and the adjustment of enterprise structure

3. Take the localization of the whole high-voltage cable industry chain as an effective means to stimulate domestic demand

II Prediction of the domestic market prospect of insulating materials for high-voltage cables

the sharp increase in the use of high-voltage cross-linked power cables in China will drive the rapid development of the high-voltage cross-linked polyethylene insulating material market. According to the development needs of the market of high-voltage cross-linked power cables, we made a prediction of China's high-voltage cross-linked polyethylene insulation material as follows:

Table 1 high-voltage cross-linked polyethylene insulation Market Prediction

we collected the specifications and samples of similar foreign products, and compared their performance with the existing domestic medium voltage insulation materials. At the same time, we also collected the national standard gb/t11017 for high-voltage cables The appendix has material requirements (see Table 2 for details), and analyzes IEC International Electrotechnical Commission standards and national high voltage cable standards. See Table 3 for relevant data:

Table 2 cross linked polyethylene plastic for domestic medium voltage power cables, national standard for high voltage cables

and comparison table of measured performance values of foreign high voltage products

from the comparison of these data, we can see that the insulating materials for high voltage cables are compared with conventional medium and low voltage insulating materials, The key lies in the improvement of impurity level, which is mainly reflected in two aspects: first, the minimum size requirement of impurities becomes smaller. The following table lists the requirements of national cable standards for impurities in cable materials; The second is the change of impurity type requirements. The insulating material for high-voltage cables requires to control the size of gel. The details are as follows:

Table 4 Comparison of requirements for high-voltage XLPE insulation and medium and low-voltage XLPE insulation. We can see from the above table that the polyethylene base material for high-voltage cables must at least meet the requirement that the maximum impurity size must be less than 0.10mm, but at present, our polyethylene base material cannot reach this level. This requirement proposed in the national standard is only the basic requirement of high-voltage cross-linked insulating materials. From our research on foreign products, we can know that compared with our current products, foreign high-voltage cross-linked insulating materials have greatly improved in electrical properties, impurity levels, impurity types, and the stability of polymer molecular weight. At present, the levels that can be achieved abroad are as follows (to significantly improve the project):

Table 5 current level of high-voltage polyethylene insulation plastic abroad (which can be used for 220kV high-voltage cables)

it can be seen that the detection and control of the impurities of base materials and insulating materials is the key to the development of insulating materials for high-voltage cables. However, it is not enough to purify only by impurity filtration and control. If domestic high-voltage insulating materials really want to reach the international advanced level, they also need the support of petrochemical enterprises for the development of high cleanliness base materials and cable manufacturing enterprises. The localization of high-voltage insulation materials is inseparable from the cooperation of upstream and downstream enterprises

IV The current situation, difficulties and potential advantages of the development of domestic high-voltage cable insulating materials

match with power cables when the calibration is completed, although China's domestic XLPE insulating materials have also experienced several years of development, at present, the highest voltage withstand grade of China's domestic XLPE insulating materials is only 35kV, and the high voltage withstand grade of 35kV and above XLPE insulating materials have been occupied by imported products for a long time, The development of domestic high-voltage cross-linked polyethylene insulation materials lags behind the development of high-voltage power cables. The main reasons for this phenomenon are:

1. China has dominated the medium and low voltage cable market for a long time, and lacks attention and Research on the high voltage cable industry chain. The consequence is the lack of technology of insulating materials for high-voltage cables, which cannot compete with foreign materials. This leads domestic cable manufacturers to rely on imports when they really need to produce high-voltage cables. In the financial crisis, foreign countries implement trade protection today, this problem is likely to continue to be amplified

2. There is a lack of highly purified and stable polyethylene based materials in China, and only a few enterprises in the world can provide them. Polyethylene base material is a key problem in the development of insulating materials for high-voltage cables. Having ultra clean high-voltage polyethylene is the premise of the industrialization of high-voltage cross-linked polyethylene insulating materials

however, we should also see that China has a broad high-voltage cable market. Once the problems of insulating material technology and base material are solved, it is very beneficial to stimulate domestic demand, develop economy and even promote the development of national industry

v As an enterprise engaged in the processing and modification of materials for wires and cables for many years, our company has rich production experience and excellent development team in insulating materials for medium and low voltage wires and cables. As early as 2006, we began to explore and study materials for high voltage cross-linked cables

unlike medium and low voltage insulating materials, there is no reference model for the development of high voltage insulating materials. We start from the mechanism and based on the medium voltage insulating materials, Establish the following development ideas:

1. Remove impurities in raw materials by certain means

2. Use impurity detection equipment to carry out central control of products

3. Adopt appropriate material transportation methods

4. Carry out air purification in the non enclosed areas of products or raw materials

5. Determine the pressure resistance grade of products with the final impurity detection results

in addition, the process route should be confirmed in the pilot test, The equipment is designed jointly with the equipment manufacturer according to the research results, forms a synchronous research topic with the main raw material suppliers, and establishes the corresponding quality control indicators

the production of high-voltage insulating materials is actually a process control, which is the inevitable choice to keep the risk in the material manufacturer. The products produced by the same process and equipment are not necessarily all qualified high-voltage insulating materials, and the qualified finished products are finally tested

VI Research and development status of new Shanghua high voltage cable insulating materials

1. Research on impurity detection methods

for the impurity detection of insulating materials for high voltage cables, a set of impurity detection methods is studied. Using CCD imaging principle to scan the thin strip extruded by the product, and using the change of impurity gray to characterize the impurities with high precision, it can not only reflect the type, size, current situation and quantity of impurities in time, but also classify the products according to the inspection results. The schematic diagram is as follows:

Figure 1 Schematic diagram of impurity detection

Figure 2. The impurities of a domestic polyethylene raw material are operated according to different standards. The detection results

2, impurity types, causes of formation, removal methods and control research of the whole process

impurity types can be subdivided into impurities, metals and gel. The causes of formation are different. Impurities mainly exist in the base material, which can be removed by filtration and selection of the base material, Metal is mainly introduced when the material is transported by air, and the removal method can start from the transportation mode

(1) filtration process

here are some test data of the test results of the size of a polyethylene impurity in China by using different filtration mesh numbers:

table 6 impurity detection after different filtration

below are the changes in the morphology, size and quantity of impurities before and after filtration. We can see that through our filtration design, the number of impurities is greatly reduced, and large polyethylene gel is filtered, This is a good illustration of the filtering effect

Figure 3 impurity morphology before filtration Figure 4 impurity morphology after filtration

(2) base material selection

another way of impurity removal method is to select the base material. Whether to obtain suitable raw materials is one of the keys to the development of high voltage cable insulation materials. By analyzing foreign products and raw materials and communicating with foreign raw material factory experts, We put forward the following requirements for insulating materials for high-voltage cables:

Table 7 requirements for polyethylene raw materials of insulating materials for high-voltage cables

(3) high purity production environment

high purity production environment is an important condition for the production of insulating materials for high-voltage cables. According to the table below, we can see that such purification level can meet the actual production needs of insulating materials for high-voltage cables

Table 8 table of purification level and corresponding impurity size (data source: ISO)

in our pilot construction, we put forward the production environment requirements of 10000 grade production environment and 1000 grade packaging and feeding ports for the insulating materials used for high-voltage cables

(4) material and product transportation

for the problem of metal impurities, we have made special treatment on the inner surface of the metal pipe that the materials may contact during air transportation, so as to minimize the generation of metal impurities during long-term transportation. In addition, the conveying air also passes through several filtration systems, which also plays a role in reducing the introduction of impurities

through the study of impurity removal methods, combined with raw materials, purification and transportation, we have obtained stable process control to ensure the low impurity of insulating materials for high-voltage cables

3. Research on formula and process technology

(1) use and selection of peroxides

as materials for medium and low voltage cables, polyethylene with excellent dielectric properties is still widely used as raw materials for insulating materials for high-voltage cross-linked cables at home and abroad, and the way of cross-linking is to adopt chemical cross-linking that can provide polyethylene with uniform and high cross-linking degree

chemical crosslinking requires peroxide. Before peroxide is added, it needs to undergo sedimentation filtration and filtration

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