Abstract: In the wind turbine transmission system, the gearbox is an important component, and the bearing is a key device that directly determines whether the gearbox can operate normally. Because the bearings are in a rolling state for a long time, faults often occur, causing the generator set to fail to operate normally. In serious cases, it will damage the service life of the power grid. The main causes of bearing failure are bearing pitting corrosion, high temperature or shaft surface wear. This article focuses on the analysis and analysis of fault diagnosis of gearbox bearings in wind turbines, and provides a reference basis for methods to solve gear bearing failures.
Keywords: wind turbine; gearbox; bearing; vibration; fault diagnosis
The bearings in the gearbox have the functions of transmitting motion, torque and speed change. Once the bearing fails, it will seriously affect the normal use of the gearbox. If gears fail, 60% of them are caused by gear failure. At present, when diagnosing gearbox faults, vibration methods, oil analysis methods, and chaos diagnosis and identification methods are used. When the gearbox enters the operating state, the components in the gearbox, including shafts, gears, bearings and other parts, will be in a state of vibration. Affected by the vibration, the bearings will suffer from pitting corrosion, or due to high temperature, shaft surface wear, etc. , causing the bearing to be unable to continue working, seriously affecting the normal operation of the generator set.
1 Gearbox failure analysis method
When a gearbox fails, the staff needs to fully analyze it, mainly analyzing the errors in the gear tooth shape, resonance in the box, bearing pitting, high temperature, shaft surface wear, shaft bending, etc. Through an in-depth understanding of the fault characteristics of the gearbox, the staff should follow the fault analysis standards and use acceleration time domain analysis, frequency domain analysis and other methods to collect the signals emitted by the gearbox under vibration and analyze the signals generated by the gearbox. Parameters such as average vibration energy and time domain peak value are used as research objects to determine the overall vibration of the gearbox. The speed time domain analysis method is used to diagnose the average vibration energy, time domain signal peak and other parameters to determine the cause of the gearbox failure. The spectrum analysis method is used to detect the meshing frequency, acceleration signal and natural frequency of the outer ring of the gearbox under the vibration state in order to find the triggering factors of the gearbox failure. At present, gearbox fault analysis is usually carried out in an industrial field environment. In order to obtain more accurate fault analysis data, the symptom status of the gear is generally detected, and the location and scope of influence of the gear fault are truly reflected. and nature, etc., to provide the necessary reference basis for the staff, so as to take targeted measures to solve the failure of the gear box.
2 Typical fault diagnosis of wind turbine transmission system
2.1 Structural diagnosis of wind turbine transmission system
At present, the generator and mechanical transmission system are important components of the wind turbine system and are responsible for stabilizing the normal operation of the generator set. In wind turbines, gearboxes, generators and bearings will frequently fail under vibration conditions. In particular, bearings are prone to pitting corrosion, shaft surface wear and other faults, and in high temperature environments, the life of the gears will be shortened. service life. In addition, as key equipment for providing kinetic energy for wind turbines, parts such as gearboxes, bearings, and couplings will be impacted by loads of varying degrees. Under different loads, it is easy to cause transmission system failures.
Figure 1 Gear box and generator measuring point distribution map
When the wind turbine is running, driven by the transmission system, the wind energy is converted into mechanical energy, and then the mechanical energy is transported to the generator, and finally electrical energy is generated. The transmission system is mainly composed of main shafts, couplings, high-speed shafts and other devices. Each device has a different structure, and the location, scope and nature of bearing failures during operation are also different. The main shaft is the key device connecting the wind wheel and the gear box. When the wind wheel rotates, it transmits energy to the gear box through changes in torque. Driven by the gear box, the axial force generated will act on other devices. A coupling is a component that connects two different devices. When the coupling rotates, it will drive the other two devices to rotate together. The power generated under different motion states requires the coupling to have functions such as buffering and vibration reduction. Couplings usually consist of a driving shaft and a driven shaft. The high-speed shaft is a device that connects the speed-increasing gearbox and the generator. The high-speed shaft remains in a high-speed state and can drive the generator to rotate at high speed to generate electric energy.
2.2 Typical fault diagnosis of wind turbine transmission mechanism
Converting wind energy into electrical energy usually requires wind turbines to operate in harsh environments such as strong winds all year round. When designing wind turbines, the minimum temperature is set at minus 20°C. However, the minimum temperature in many areas can be as low as minus 40°C, and wind turbines also need to withstand strong winds, which will increase the load on the unit. It is very easy to cause transmission system failure. Especially in mechanical transmission devices, bearings will suffer from pitting corrosion or shaft surface wear. If the staff fails to solve the fault in time or fails to replace the faulty parts, the scope of the fault will continue to expand, eventually leading to the failure of wind power generation. The machine is damaged.
2.2.1 Gearbox fault diagnosis
Parts such as gears, rolling bearings and shafts are important parts of the gearbox. When analyzing faults in gears, rolling bearings and shafts, the cause of the gearbox failure can usually be determined with the help of vibration signal frequency characteristics and fault characteristics. Wind turbines usually maintain a high speed during operation. Once a fault occurs, the parts in the gearbox will produce noise and be accompanied by irregular vibrations. When detecting the time domain, frequency domain and amplitude of the vibration signal, the staff will obtain a lot of fault data, the most obvious is gear fault and rolling bearing fault data. Once the operating speed of the wind turbine increases, the above faults will Appear.
Wind turbines are usually located in environments with strong winds, generally in harsh areas such as wilderness and islands. The load generated by wind has irregular characteristics and will produce a strong impact on the wind turbine in an instantaneous state, which will cause damage to the wind turbine. Causes failure of wind turbines. At present, the maximum speed of wind turbines can be as high as 1,500 revolutions per minute. During long-term high-speed operation, the gearbox will generate high temperature and heat. At the same time, under the action of load, the gearbox will malfunction. At present, common faults in gearboxes include local faults and distributed faults. Local faults include gear damage, bending fatigue, etc., and distributed faults include tooth surface wear, bearing damage, etc. The fault forms that occur include the following: First, broken teeth. After the gear is subjected to periodic stress, cracks will appear at the root, and after a long period of load, the gear will have broken teeth; secondly, gear tooth surface fatigue. When the gearbox is in motion, it is affected by mechanical mechanics, and the force generated causes the gears to slide relative to each other. However, pitting corrosion, destructive pitting corrosion, and surface crushing occur on the tooth surface. The gear tooth surface appears in a fatigue state, and the fault state is manifested by the meshing frequency of the vibration signal, an increase in vibration energy, an increase in energy amplitude, etc.; third, the tooth surface is glued. After the gear is subjected to high-speed and heavy load, the gear box is in a high-temperature state. At this time, the tooth surface is affected by high temperature and pressure, and wear and other conditions will occur on the tooth surface. In addition, when the gears are relatively sliding, the teeth The surface is not sufficiently lubricated, resulting in gluing failure on the tooth surface.
2.2.2 Rotor misalignment fault diagnosis
Wind turbines are large mechanical equipment. The generator sets are usually placed tens of meters above the ground, and are affected by the wind. It is difficult to install bulky generator sets, and it is impossible to ensure accurate centering of the rotor. If the rotor fails to remain in the aligned state, during long-term operation of the generator set, under the combined influence of wind and high operating temperatures, the damper in the gearbox will deform, causing the rotor and bearings to be unable to remain in the aligned state. , at this time, the power station unit will vibrate irregularly, causing the axes of the front and rear rotating devices to be unable to remain in the same straight line, causing bearing failure. Rotor misalignment failure is not only difficult to install, but also caused by the following reasons: First, the rotor in motion will cause different differences between the driven rotor and the active rotor due to changes in this variable. Dynamic conditions; second, different expansion conditions occur in the bearing seat of the rotor; third, deformation or displacement of the casing; fourth, uneven settlement of the foundation where the generator is located; fourth, bending of the rotor, causing the unit to An unbalanced rotation condition occurs.
2.2.3 Rolling bearing fault diagnosis
In the transmission system, rolling bearings are important devices. Rolling bearings generally consist of an inner ring, an outer ring, rolling elements and a cage. The installation of rolling bearings in the generator set takes advantage of the advantages of rolling bearings such as high efficiency, easy lubrication and low friction resistance. However, rolling bearings will make loud noises during use, and at the same time, they cannot withstand large impact forces. If the rolling bearing fails, it can easily cause extensive damage to the generator set. When analyzing rolling bearing faults, the main fault characteristics are divided into the following aspects: First, the inner ring of the bearing appears to be peeled off or pitted. When the spectrum is used to detect the inner ring, there will be obvious harmonic changes; secondly, there will be peeling or pitting corrosion in the outer ring. Using spectrum for detection, the fault characteristics at this time are no frequency conversion and no amplitude modulation; third, when the rolling elements are peeled off or pitted, obvious modulation peak group characteristics will appear at the fault location; fourth, the cage is deformed or fall off. Using spectrum for detection, it was found that characteristic frequencies and harmonics appeared in the cage. In addition, the failure forms of rolling bearings are divided into the following types, namely fatigue spalling failure, wear failure, crack and fracture failure, and indentation failure.
2.2.4 Generator fault diagnosis
Generator failures can be divided into stator winding failures and bearing failures. When a stator winding failure occurs, the winding will be damaged, worn, cracked, etc. At this time, the winding cannot provide insulation function. When a bearing fault occurs, faults in different parts will produce different vibration signals. Taking rotor misalignment as an example, such problems will be classified as eccentric faults. In addition, the rotor and stator are supported by bearings, and the bearings will bear large radial loads. Under the action of large loads, the bearings will fail. Under normal circumstances, bearings will suffer damage, pitting, and wear to the inner and outer rings, and the vibration of the bearing will increase the probability of failure.
3 Conclusion
To sum up, when a wind turbine fails, it is necessary to determine the cause of the failure of the wind power system from a scientific perspective. Once a wind turbine unit fails, staff should fully analyze the traditional systems in the unit and investigate the fault factors of different devices in the system one by one. However, due to the influence of fault diagnosis conditions, the failure of the gearbox bearing in the generator set can only be simulated and analyzed through theoretical basis and experimental methods, and accurate data cannot be obtained through online testing. When analyzing gearbox bearing faults, technologies such as composite fault diagnosis and hybrid intelligent fault diagnosis should be used as fault detection methods to help improve detection efficiency and efficiently handle bearing faults.
references:
[1] Wang Chaohui, Cui Houxi. Application of cepstrum analysis method to fault diagnosis of wind turbine gearbox
[2] Fu Zhi, Guo Bojiang. Research on fault diagnosis of wind turbine gearbox bearings
[3] Liu Chenghao, Ma Yuze. Wind turbine gearbox vibration test and analysis
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