1 Overview of foreign wind energy development According to statistics, the global wind energy resources are at 500,000 TW*h/year. Considering factors such as society and geographical environment, the actual wind energy resources that can be developed are about one-tenth of the total wind energy resources. Wind power originated in the 1970s. Due to the dual pressures of the environment and energy, the U.S. government gave a priority to the development of wind power. The series of preferential policies has promoted the development of wind power, and it has also enabled people to truly understand wind power. Wind power technology matured in the 1980s. Since many countries have successively established wind power scientific research institutions and development departments, the single machine capacity of wind turbines has doubled, and its availability has also been increased to over 95%, making wind turbines practical targets. Grid-connected wind turbines were successfully developed from 20 to 50 kW in the 80's to 500 to 800 kW in the 1990s and 1 to 2 MW in the mid-90's. They were commercialized. At present, 3 ~ 6MW prototypes have been successfully developed and will be mainly used in offshore wind farms. The main investors in wind power have undergone major changes. Countries, regions, power departments, financial institutions, and consortia have all raised funds for wind power development and construction. Wind power worldwide is growing at a rate of 30% every year. The cumulative installed capacity of the world for the year is shown by.
From a worldwide perspective, German wind power is the largest in the world, with a cumulative installed capacity of 6,107 MW. The total installed capacity of the United States is the world's largest installed capacity of the top four manufacturers in 1998 accounted for 70% of the market share. According to the Danish Wind Turbine Manufacturers Association According to statistics, in 1998, Danish manufacturers produced 1210MW wind turbines with a production value of 1 billion U.S. dollars. It is speculated that global wind turbine manufacturers will sell 2 billion U.S. dollars. The average annual growth rate of the wind turbine manufacturing industry in the 1990s reached 30%, and it will have the same growth rate in the coming years. Wind turbine manufacturing is one of the fastest growing industries in the world.
2 Overview of China's wind energy development China's wind energy resources are extremely rich. The theoretical reserve is 1.6 billion kW, and the total amount of wind energy resources that can be exploited and utilized in the country is 253 million kW, which is greater than the country's hydropower resources. According to the conditions of resources, land, transportation, and power grids, it is determined that there are about 50 wind farms with development conditions in the near future, distributed in 11 provinces across the country, including Xinjiang Daban City, Inner Mongolia Huitengxile, Hebei Zhangbei, Jilin Tongyu, Shanghai Chongming, Guangdong Nanao and other places all have the conditions for installing 100MW. Since the 1970s, the state has encouraged the development of small, stand-alone wind turbines in order to solve the problem of electricity use in western pastoral areas, eastern islands, and remote mountainous areas. Domestic wind power scientific research institutions are mainly engaged in the research and development of small wind turbines and form a considerable scale. At present, there are 180,000 such wind turbines in China, and 600,000 residents in areas where the grid cannot reach solve the power problem. The production capacity, production volume, and social possession of small wind turbines in China are the highest in the world.
In 1993, China explicitly proposed that wind power should be used as an industry. In the past few years, the country formulated the “Wind by the Wind†plan. This plan aims to establish a joint venture, introduce technology, and through digestion and absorption, achieve independent development and design and manufacture of large-scale wind turbines. The House has also formulated a "bright project" to develop and utilize renewable energy sources, including wind energy, to provide electricity for areas far from the grid. Thanks to the support of the government, in the mid to late 1990s, China’s wind power achieved considerable development. The number and scale of wind farms gradually expanded, and many successful experiences in construction, operation, and management were achieved. The initial development of wind power was scale-up. The ability and conditions. At present, more than a dozen companies in the country are engaged in the construction and development of wind farms with a capacity of 2,610 MW, 2,341 MW in Denmark, and 2,836 MW in Spain. Wind power in Europe accounts for 75% of the world. According to the plan, the installed capacity in Europe in 2010 will reach 40,000 MW by 2020. Annually reached 100,000 MW. Denmark plans that by 2030, renewable energy including wind energy can provide 40 to 50% of the country's electricity consumption. In the past 20 years, the wind turbine industry has developed into a professional high-tech industry. Wind turbine manufacturers are concentrated in a few companies, most of them European companies. For the world's top ten wind turbine manufacturers cumulative production in 2000.
camp. There are more than 20 wind farms of different sizes installed, and the installed capacity has exceeded 400 MW. It is an annual cumulative installed capacity in China.
According to the plan, the cumulative installed capacity in China will reach 1500MW by 2005, the installed capacity will reach 4000MW from 2006 to 2010, and the total installed capacity will reach 7000MW from 2011 to 2015. 3 Blade technology advances with the increasing capacity of wind turbines. The length also increases. From the 200KW wind turbine blade length of 10m to a length of 21m of 600KW. 1~2MW wind turbine blades are 30~40m in length. The longest blades are currently about 60m long. The increase in blade length has greatly increased the difficulty of blade design, materials and manufacturing. Therefore, the progress of large-scale blade technology is the progress of design, materials, processes, and equipment integration technologies.
In addition to the significant increase in installed capacity, the development of wind power has a very significant technological development. From the power regulation, four kinds of technologies are currently prevailing in the world: award-winning stall control, variable pitch, active stall control, variable speed constant frequency. Most of the current MW wind turbines use variable speed constant frequency technology. The different adjustment methods of the wind turbine have special requirements for the aerodynamic design of the blade and even the structure of the blade. The blade is one of the key components of the wind turbine, involving pneumatic, composite material structure, technology and other fields, especially the design and manufacture of the MW-class large-scale composite material blade is very difficult. Therefore, its price accounts for about 18% to 22% of the unit. Foreign leaves are specialized in production and are concentrated in several specialized companies. The most famous blade company is Denmark's LM company. By 2000, it had produced 60,000 blades. In that year, it produced 7,200 blades, which accounted for 45% of the world market. There are 12 factories in the world, and it employs 2,200 people. Global sales service network. There is a department specializing in the research and development of blades at the headquarters. The main topics are blade structure dynamics, lightning strikes, pneumatics, and structural tests. Vesta, one of the world's top ten manufacturers of wind turbines, supports its own production of blades. Its wind turbines account for 17% of the world market. Germany's NOI mainly produces MW wind turbine blades. In recent years this monopoly by specialized blade manufacturers has been broken. Some well-known wind turbine manufacturers began to produce their own blades, such as Nodex's 1.5MW variable-pitch blades. Other large companies such as Bonus, Game8e, and Enercon are also developing MW blades.
China has a certain gap with foreign countries in the design and manufacturing technology of FRP blades. Blade technology is a key technology for wind turbines. Foreign large companies are not willing to transfer technology or co-produce them. In order to make glass fiber reinforced plastic blades domestically, the relevant government departments attach great importance to the research and development of the blades and support the research and development projects of the blade. Research projects include "Seventh Five-Year Plan" "Study on FRP Blades for Small Wind Turbines", "Eight-Five-year Development of Fifty-Five 200KW Wind Turbine FRP Blades" and "Development of FRP Blades for 300KW Wind Turbines", Special Fund for Scientific Research Institutes * 660KW Wind Turbine FRP Blade Industry ". During the “15th Five-year Plan†period, the country listed MW-class wind turbines as a *863* project, including a 1.3MW fixed-pitch stall control wind turbine, a 1MW, and a 1.5MW variable-speed constant-frequency wind turbine. The supporting blades are listed as special sub-topics. After many years of research, China has developed 200-750KW series of large-scale wind turbine FRP blades, forming a batch of children's production, laid the foundation for the localization of wind turbines.
4 Problems in Blade Technology Aerodynamic design includes wind turbine aerodynamic design and aerodynamic performance calculations. According to the overall performance requirements of the wind turbine, the diameter of the rotor, the number of blades, the rotation speed, the chord length, the blade thickness, and the twist angle distribution were determined. The aerodynamic shape design can use Wilson's pneumatic performance optimization aerodynamic shape. The theoretical design shape must be corrected considering the blade structure and process requirements. When the aerodynamic shape is determined, the aerodynamic performance can be calculated. For wind turbines with fixed pitch stall control, parameters such as output power, Cp value and thrust of wind turbines with different installation angles should be obtained to determine the initial installation angle of the blades and the stall performance of the wind turbine. For a variable pitch variable speed wind wheel, the wind wheel performance with different installation angles and different rotation speeds is calculated to determine the adjustment mode of the wind wheel operation. Wind turbine blades are developed from conventional NACA44 and NACA230 airfoils to wind turbine-specific airfoils, such as NACA63, FX77, and NREL-S. These airfoils have a relatively high lift-to-drag ratio, and aerodynamic performance is insensitive to blade surface contamination. China has not yet developed its own airfoil type, and it has adopted foreign ones. Since no complete aerodynamic performance data was collected on the airfoil, the aerodynamic design of the blade was significantly affected.
Commercial large-scale wind turbine blades have a typical structural form. The root forms of the blades are mainly glued metal flanges, such as those produced by Vestas; glued metal bolts, such as LM blades; T-bolts, such as blades produced by NOI, Aerpac. The root end of the above-mentioned form has a relatively large carrying capacity, the curve of the root end transition section is soft, and the weight is lighter, so that the bulky appearance of the flanged flange is changed. The profile of the blade basically adopts the structure of the skinned main beam. The main girder may be in the form of an integral box girder, such as Vestas blades, or in the form of double channel steels, such as LM blades, or with stiffener structures. At the front and rear edges of the profile, the stability calculation is used to determine whether the sandwich structure is used. Most of the bending load on the blade is borne by the main beam. The skin plays aerodynamic shape and can take part of the load. This section structure can reduce the weight of the blade, mention the strength and rigidity of the blade, and avoid the local instability caused by the bending of the blade. Blade skins are usually reinforced with felt or bi-directional fabrics. The main beam is reinforced with a higher degree of unidirectional fabric to increase strength and stiffness. The core material can be PVC foam or Balsa wood. With the increase of length, the weight of FRP blades increases greatly. The radius of the blades and the radius of the rotor are approximately R29. For example, the single blade weight of 40m long blades is 10T, and the single blade weight of 50m long blades is 16T. The weight of blades increases, and the weight increases. The fatigue load caused by the blade's own weight also increases the load on other components of the unit. To reduce blade weight, carbon/fiber hybrid reinforcement can be used, such as carbon fiber reinforced main beams, or all carbon fiber reinforced blades. Some foreign experts pointed out that the blade is larger than 40m, carbon fiber should be used, but LM company believes that even larger blades, in theory, can also be used glass fiber reinforced plastic, glass fiber / epoxy solution can be used. Even so, the company is also conducting research on carbon fiber blades. Currently, Nodex has developed a 43.8m carbon/*fiber hybrid blade with a weight of 9.6T. Enercon is developing a carbon fiber blade with a diameter of 112m for the wind turbine, which is used for 4.5MW commercial onshore and offshore wind farms. Enron and N0I's Vestas are also developing carbon fiber blades for applications ranging from 3 to 5 MW offshore/onshore commercial aircraft. According to European and American experts, the carbon/glass hybrid enhancement can reduce the blade weight by 30% and reduce the cost by 15% for MW-class large-scale wind turbine blades. It also reduces the national standards for blade tip rotor blades and certification of wind turbines by China Classification Society. The specifications all require a blade structure test to verify the accuracy of the design and the quality of the manufacturing process. The structural tests mainly include the static strength and stiffness of the blade under design load, the first-order flapping and pendulum frequency of the blade, and the fatigue test. Foreign wind turbine manufacturing industry in developed countries such as Denmark, the Netherlands, and the United States all have national blade testing centers and are authorized by the government to conduct blade certification. China has not yet established a national wind turbine testing center, and structural tests of blades have been conducted at the factory under the guidance of classification societies.
The full-scale blade fatigue test is an important test content and it is verified in the laboratory whether the blade can be used for 20 years. According to the fatigue load spectrum of the blade, the fatigue load alternating time reaches 10* order of magnitude in the 20-year service life. The frequency of fatigue loading is generally the first-order frequency of the blade. For a large blade at around 1 Hz, the loading speed is 1 to 2 times/8. To accelerate the fatigue test speed, the load should be increased, and the loading frequency is generally 100 to 5 million times. 2~3 months. The test load spectrum should be determined according to the damage equivalent principle. We conducted 300 kW and 660 kW blade fatigue tests in laboratories. The tests were carried out 5 million times and passed the certification of the classification society.
Most of the large wind turbine blades use open mold technology. The aerodynamic surface and the working surface half shell are formed on two female molds respectively. The main beam of the blade and other glass steel components are formed on special molds, and then glued and assembled into integral blades. The blade forming process has evolved from an early hand lay-up process to a more advanced process. Such as LM company uses VARTM process. The application of this process solves a series of technical problems of molding large glass steel components. This technology can increase fiberglass fiber content and increase strength. Vestas uses a prepreg process. The German NOI company uses a wet prepreg process. Because of the influence of market, technology, and funds, most manufacturers of FRP blades in China use the wet hand lay-up process and cure at room temperature. The process is relatively simple and does not require warming and pressurizing devices. With the development of China's wind power industry, the market needs more quality glass fiber reinforced plastic blades, the use of advanced molding process is the only way. At present, domestic manufacturers have begun research work in this area.
Most countries in the world require the installed wind turbines to be certified to ensure their quality. The EU proposes to adopt the IEC standard uniform certification rules and requirements. The technical standard relating to blades in the IEC series of standards is IEC1400 -1* Wind Turbine System Safety. This standard stipulates the conditions of blade load, local safety factor, inspection requirements, etc.; IEC1400 -23* Wind Wheel Blade Measurement Technology.†It specifies the method for static stiffness measurement, frequency measurement and fatigue testing of blades. China Wind Turbine Standards Committee A series of standard specifications have been formulated, among which the standard for large-scale wind turbine blades is “wind turbine blades for wind turbines.†This standard basically refers to the IEC standard and Lloyd's standard. In terms of structural design, etc., China Marine Classification Society has established a wind turbine certification standard, and the promulgation and implementation of national standards and certification standards enables domestic manufacturers to design and produce complete machines and components in accordance with internationally equivalent technical requirements. Quality control enables products to participate in domestic and international competition at a high starting point.
5 The important components such as the main shaft, transmission and motor applied to the nacelle cover and the shroud are all installed in the nacelle cover. Therefore, the nacelle cover mainly protects the equipment from the environment and provides personnel installation and maintenance conditions. The diversion is mainly used to improve the aerodynamic performance of the wind wheel. Although the technical content of these two components in the unit is not good, the manufacturers of wind turbines have very few requirements for their manufacture because the appearance quality has an impact on the manufacturer's brand. I worked with Vestas to produce nacelle covers and shrouds for 660 kW units. Under the guidance of the experts of the other party, the company uses the other party's technology to manufacture molds and products. Currently, it has been able to mass-produce fiberglass cabins and shrouds for domestic wind turbine manufacturers.
6 Conclusion Wind energy is one of the fastest growing few industries in the world today. With people's increasing emphasis on energy crisis and environmental issues, it is expected that wind energy will continue to maintain rapid growth for a long period of time, and it will also become an important application field for FRP composite materials.
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