The gearbox in a wind turbine is an important mechanical component, and its main function is to transmit the power generated by the wind wheel under the action of the wind to the generator and make it get the corresponding speed.
Introduction:
Generally, the rotation speed of the wind wheel is very low, far less than the rotation speed required by the generator to generate electricity. It must be realized by the speed increasing effect of the gear pair of the gear box, so the gear box is also called the speed increasing box. According to the general layout requirements of the unit, sometimes the drive shaft (commonly known as the large shaft) directly connected to the wind wheel hub is integrated with the gear box, or the large shaft and the gear box are arranged separately, during which expansion sleeves or couplings are used Connected structure. In order to increase the braking capacity of the unit, a brake device is often installed at the input or output end of the gearbox, and combined with blade tip braking (fixed-pitch wind wheel) or variable-pitch braking device to jointly brake the transmission system of the unit .
note:
As the unit is installed in vents such as mountains, wilderness, beaches, islands, etc., it is subject to irregular changes in direction and load and the impact of strong gusts. It is subjected to severe heat and cold and extreme temperature differences all year round, and the natural environment is inconvenient for transportation. The gearbox is installed in the narrow space on the top of the tower. Once it fails, it is very difficult to repair it. Therefore, its reliability and service life are much higher than those of ordinary machinery. For example, the requirements for component materials, in addition to the mechanical properties under normal conditions, should also have characteristics such as cold brittleness resistance under low temperature conditions; the smooth operation of the gearbox should be ensured to prevent vibration and shock; adequate lubrication conditions should be ensured, and so on. For areas with huge temperature differences between winter and summer, appropriate heating and cooling devices should be equipped. Also set up monitoring points to remotely control operation and lubrication status.
Different forms of wind turbines have different requirements, and the layout and structure of gearboxes are therefore different. In the wind power industry, fixed parallel shaft gear transmission and planetary gear transmission are the most common for horizontal axis wind turbines.
Influence of natural conditions:
Wind power generation is affected by natural conditions. The emergence of some special meteorological conditions may cause the wind turbine to malfunction. The small nacelle cannot have a solid base like on the ground. The power matching and torsional vibration of the entire drive train Factors are always concentrated on a weak link. A lot of practice has proved that this link is often the gearbox in the unit. Therefore, it is particularly important to strengthen the research on the gearbox and pay attention to its maintenance.
Through the introduction of advanced technology from German RENK, the company has successfully developed various marine and land-use wind power gearbox series products ranging from 1.5MW to 5MW. At present, 5MW wind power gearbox prototypes have been connected to the grid for power generation, and mass production has been achieved, and the on-site operation is in good condition. The overall scheme design of wind power gearboxes can be designed with different speed ratio structures according to user requirements, and can also be designed with high prototype, high temperature, low temperature and low wind speed type speed increasers according to user requirements.
Increased unit capacity of single unit The increase of unit capacity of wind power unit is conducive to improving the utilization rate of wind energy, reducing the footprint of the wind farm, reducing the operation and maintenance cost of the wind farm, and improving the market competitiveness of wind power.
On the one hand, all offshore wind turbines are transformed from onshore wind turbines, and the complex offshore natural conditions make the failure rate of wind turbines remain high, such as the world’s largest offshore wind farm in Denmark’s Horn Reef Wind Farm, 80 offshore wind farms The unit failure rate exceeds 70%. On the other hand, the grid will not be able to withstand the huge power provided by large-scale offshore wind power sites. Therefore, the large-scale development of offshore wind power still needs to solve the problems of generating units and supporting facilities for the Internet.
Variable-speed constant-frequency technology is quickly promoted. At present, wind turbines operating at constant speed on the market generally adopt asynchronous generators with a dual-winding structure and operate at two speeds. In the high wind speed section, the generator runs at a higher speed; in the low wind speed section, the generator runs at a lower speed. Its advantages are simple control and high reliability; the disadvantage is that the rotation speed is basically constant and the wind speed often changes, so the unit is often in a state with a low wind energy utilization factor, and wind energy cannot be fully utilized.
With the advancement of wind power technology, wind turbine development and manufacturers began to use variable-speed constant-frequency technology, and combined with the application of variable-pitch technology to develop variable-pitch and variable-speed wind turbines. Compared with wind turbines operating at constant speeds, wind turbines operating at variable speeds have the advantages of large power generation, good adaptability to changes in wind speed, low production costs, and high efficiency. Therefore, variable-speed wind turbines are also one of the future development trends. German companies are currently the company that produces the most variable-speed wind turbines in the world.
Direct-drive and semi-direct-drive wind turbines Direct-drive wind turbines use multi-pole motors and impellers directly connected for driving, eliminating the need for gearboxes with high failure rates, high efficiency at low wind speeds, low noise and long life , The advantages of low operation and maintenance costs. In recent years, the share of installed capacity of direct-drive wind turbines has increased significantly, but due to technical and cost reasons, wind turbines with speed-increasing gearboxes will still dominate the market for a long time in the future. Semi-direct drive is a drive mode between gearbox drive and direct drive. It uses a first-stage gearbox to increase speed, has a compact structure, and has a relatively high speed and a small torque. Compared with the traditional gearbox drive, the semi-direct drive increases the reliability of the system; and compared with the large-diameter direct drive, the semi-direct drive reduces the volume and weight of the system through a more efficient and compact cabin arrangement.
The external gears of wind power gearboxes generally adopt the carburizing quenching gear grinding process. Due to the introduction of a large number of high-efficiency and high-precision CNC forming gear grinding machines, the finishing level of wind power gearboxes has been significantly improved. The large ring gear size and high machining accuracy requirements of wind power gearboxes should be reflected in the tooth-making process and heat treatment deformation control of the helical internal gear.
The machining accuracy of the case, planet carrier, input shaft and other structural parts of the wind power gearbox has a very important influence on the meshing quality of the gear transmission and the life of the bearing. The quality of the assembly also determines the life of the wind power gearbox. The level of reliability. Therefore, the acquisition of high-quality and high-reliability wind power gearboxes requires strict quality control in every aspect of the manufacturing process, in addition to the design technology and necessary manufacturing equipment support.
For the main gearbox of a wind turbine, once the oil is polluted by water and cannot be found and treated in time, the impact is undoubtedly fatal. This includes reducing the viscosity of the oil, destroying the oil film, accelerating the oxidation of the oil, leading to the precipitation of additives, and then Cause parts damage.
In order to ensure the safety of the oil in the main gearbox of the fan, preventing water from entering the system is an effective way to deal with water pollution, such as regular replacement and installation of moisture-proof respirators, but when the system is polluted by water, corresponding treatment methods should also be taken .
Install a suction tube in the bypass filter system of the wind turbine gearbox, built-in super absorbent polymer, the water absorption efficiency is as high as 95%. The oil is heated, and the water evaporates in the dryer without causing the oil to be oxidized at excessively high temperatures. The high-vacuum dehydration machine can remove 80% to 90% of the dissolved water.
A large part of the failures of wind power gearboxes are caused by gears. The gear operating environment is more complicated, long-term overload, poor lubrication, incorrect installation of bearings or gears, and poor meshing of the gears themselves will cause gear failures and shortened life. .
Vibration detection is currently a comprehensive and effective detection method for detecting wind power gearbox failures. As long as the use of suitable vibration detection equipment to collect data and analyze can determine the operation of the gear, timely repair and replacement of faulty parts to ensure the normal operation of the equipment, even Prevent early failures to extend the life of components.
When the gear of a wind power gearbox wears, the amplitude of the sideband of the meshing frequency will increase significantly. In severe cases, the natural frequency of the gear will appear and there will be frequency modulation. Generally, when the load is high, a very high meshing frequency and its harmonic frequency will appear. The gear meshing frequency and its harmonics are modulated by the rotation frequency, and natural frequency vibration occurs; when the gear is misaligned, higher harmonics of the gear meshing frequency are generally generated, and the amplitude of the first frequency is lower and the amplitude of the two times and three times is higher.
After the vibration data is collected, the meshing frequency of the gear can be calculated according to the data such as the number of teeth and the speed of the wind power gearbox, and the characteristics in the time domain or frequency spectrum can be used to diagnose the fault of the gearbox. However, in practical applications, because there are multiple sets of gears and bearings in the gearbox, the speed is not static. Spectrum analysis often has various frequencies, some of which are very close, making it difficult to identify.
At this time, we need to combine the amplitude analysis based on the position of the measuring point. For each gearbox, when it is in good working condition, collect the reference frequency spectrum, and compare it with the reference frequency spectrum in condition monitoring and fault diagnosis. problem.
Wind power generation uses wind to drive the rotation of windmill blades, and then increase the speed of rotation through a speed increaser to promote the generator to generate electricity. According to the current windmill technology, power generation can start at a breeze speed of about three meters per second.
The wind turbine is composed of a nose, a rotating body, a tail and blades. Each part is important. The blades are used to receive wind and turn into electricity through the nose; the tail keeps the blades always facing the direction of the incoming wind to obtain large wind energy; the rotating body can make the nose flexibly rotate to realize the function of adjusting the direction of the tail ; The rotor of the machine head is a permanent magnet, and the stator winding cuts the magnetic lines of force to generate electricity.
The nacelle contains the key equipment of the wind turbine, including gearboxes and generators. Maintenance personnel can enter the nacelle through the wind turbine tower. The left end of the nacelle is the rotor of the wind turbine, namely the rotor blades and shaft. The rotor blades are used to catch the wind and transmit it to the rotor axis.
The low-speed shaft of wind power generation connects the rotor shaft with the gear box. The low-speed shaft is on the left side of the gear box, which can increase the speed of the high-speed shaft to 50 times that of the low-speed shaft. High-speed shaft and its mechanical brake: The high-speed shaft runs at 1500 revolutions per minute and drives the generator. It is equipped with an emergency mechanical brake, which is used when the aerodynamic brake fails or when the wind turbine is being repaired.
The electronic controller of wind power generation includes a computer that constantly monitors the status of the wind power generator and controls the yaw device. In order to prevent any malfunction, the controller can automatically stop the rotation of the wind turbine and call the wind turbine operator through the telephone modem.
The hydraulic system of wind power is used to reset the aerodynamic brake of the wind generator; the cooling element contains a fan to cool the generator. In addition, it contains an oil cooling element for cooling the oil in the gearbox. Some wind turbines have water-cooled generators.
