The wind power generation equipment is expensive, the operating environment is harsh, and the disassembly cost is high. Once it fails, it may cause huge claims. Therefore, the wind power generation unit requires a life of not less than 20 years and a warranty period of 5 years. During the design, manufacture, installation and use of slewing plate bearings, various failures will occur, including: Pitting wear of rolling elements and raceways leads to increased clearance, no oil-free dry friction, broken cages, serious rolling elements and raceways Wear and pits appear, the connecting bolts between the inner and outer rings and the upper and lower metal structures are loose, and the metal structure has cracks. These faults can be manifested by vibration. In the actual use process, there will also be problems such as the increase in the temperature of the raceway grease and the increase in the power of the driving motor. However, due to the low rotational speed (1-26 r/min) of the wind turbine slewing bearing, the large load (the mass of the blade and the nacelle reaches more than ten tons), and the insensitivity to the generated vibration, some faults are not easy to be found.
At present, the problems faced in the fault diagnosis of wind turbine turntable bearings are: (1) The bearing speed is very low, and the calculated fault frequency is very low. The high-pass filter will filter out the frequencies below 3 Hz, and the influence of environmental noise will make the spectrum analysis very poor or even impossible; (2) The interval between each fault impact is long, and it is difficult to use the impact method to accurately (3) The impulse response frequency generated by the fault point is low, and the higher frequency components cannot be excited.
Wind power slewing bearings usually only reciprocate in a small range, and in many occasions, they are in a static state for a long time and bear complex alternating loads at the same time. Therefore, its failure mechanism is different from the rolling contact fatigue of ordinary bearings, and the design theory of ordinary bearings cannot well solve the design and quality problems of slewing bearings. There is very little experience for its fault diagnosis. Therefore, how to solve this problem has become a research hotspot in various countries. The world's major well-known companies have their own laboratories and test equipment, but they are always in the stage of technical blockade, and only publish partial pictures related to the test in advertisements or websites. On the basis of years of experimental research, the load-bearing stiffness, raceway wear, starting torque, fatigue life and tooth root strength of wind turbine slewing bearings are studied. It is believed that the main parameters for fault diagnosis and detection of wind turbine slewing bearings are: , raceway wear, vibration acceleration, friction torque, raceway cracks, grease temperature and drive motor power, etc., but the parameters that characterize the performance characteristics of wind turbine slewing bearings need to be further discussed in combination with experiments.
1 Bearing fatigue life test
1.1 Test device
As shown in Figure 1, the comprehensive performance test device of wind turbine slewing bearing consists of mechanical part, hydraulic system and measurement and control system. The test device is loaded by a hydraulic cylinder, which can simultaneously apply axial force, radial force and overturning moment to the bearing. The hydraulic motor drives the turntable bearing to rotate to simulate the actual operating state of the bearing. At the same time, the data is collected through the test sensor, and stored and processed.
Fig. 1 Schematic diagram of comprehensive test device for wind turbine slewing bearing
1.2 Detection parameters
Once the slewing bearing fails, its vibration, temperature, friction torque, noise and tooth root stress will all change. Through the corresponding signal processing technology, the useful characteristic parameters that can characterize the bearing operating conditions can be extracted from the complex signals, and the diagnosis of the slewing bearing can be realized by analyzing these characteristic parameters. The friction torque can reflect the working performance, power consumption, life and safety performance of the wind turbine slewing bearing. It mainly comes from the contact friction resistance between the rolling element and the raceway. It is generally believed that the friction torque is mainly caused by the external load. When the slewing bearing fails, the running resistance will increase. In view of the randomness and complexity of the friction torque of the slewing plate bearing, it is difficult to obtain the accurate value by the method of theoretical analysis. Therefore, the friction torque of the slewing plate bearing can be detected by experiments, and the performance and operation of the bearing can be evaluated based on this.
Under normal circumstances, the friction of the slewing bearing consumes energy in the form of heat, and the temperature rise of the slewing bearing friction is affected by the heat generated by each motion pair and the room temperature. When the slewing bearing starts to run, due to the rise of friction running-in temperature, after running for a period of time, the temperature balance is reached, and the change of raceway temperature remains relatively constant with the ambient temperature. When the raceway is peeled off, iron filings are mixed into the grease, and the ball and the raceway are worn, resulting in an increase in the friction torque of the bearing, causing heat generation, and further increasing the temperature rise of the slewing bearing. The increase in temperature can easily lead to partial burns of bearing parts, destroy the lubricating film, and aggravate bearing wear. Therefore, it is very necessary to monitor the temperature of the slewing bearing.
The vibration analysis of the turntable bearing is the most effective diagnostic method. According to the previous test results, the vibration direction of the turntable bearing is located in its axial direction, close to the drive motor. In order to study the parameters that characterize the operation of the slewing bearing, the temperature rise, friction torque and vibration acceleration of the wind turbine slewing bearing were detected. The sensor layout of the test rig is shown in Figure 2, where the temperature sensor is placed in the mounting hole and in contact with the grease.
Fig. 2 Sensor layout of wind turbine slewing bearing test device
1.3 Test bearing parameters
Accelerated life test was carried out on a company's 033.50.2410 wind power slewing bearing. The test bearing parameters were: the center diameter of the channel was 2410 mm, the diameter of the steel ball was 50 mm, the number of balls was 140, the contact angle was 45°, and the number of external teeth was 135. The bearing is a double-row four-point contact ball bearing, the outer ring is a gear ring, the material is 42CrMo, and the steel ball material is GCr15. When the number of stress cycles reaches 1 million, the theoretical fatigue limit of the material is reached. In the test, the maximum rotation of the turntable bearing is 1.5r/min, 50% of the full load, and the test runs for a total of 71.6 days.
2 Test results and analysis
2.1 Fault Characteristics
After the test, the slewing bearing was disassembled, and the damage of the steel ball and the channel was checked. The inner and outer ring soft belts were peeled off. The surface of the rest of the channel was smooth, with a small number of slight indentations in the local area, and no other damage such as pitting occurred. The steel ball is not damaged. The topography of the inner channel of the slewing bearing is shown in Figure 3.
Fig. 3 Morphology of the inner channel of the slewing bearing after the fatigue test
2.2 Analysis of detection parameters
2.2.1 Trend analysis of friction torque
The variation law of the friction torque of the test bearing is shown in Figure 4. According to the analysis of the fitting curve, the wind turbine slewing bearing has a negative clearance fit at the beginning of operation, and the frictional resistance is the largest at this time. The smallest, only 8. 096 kN m. With the pitting of the soft belt in the channel due to wear, the iron filings enter the grease, resulting in increased friction and increased friction torque. Therefore, the friction torque can be used as an effective parameter for judging the wear condition of the slewing bearing raceway. For real-time judgment, a mathematical model needs to be established for quantitative judgment.
Time/Days
Fig. 4 Friction torque curve and fitting curve
2.2.2 Analysis of temperature rise change of lubricating grease
The variation trend of grease temperature rise and its fitting curve are shown in Figure 5. It can be seen from Figure 5 that the temperature rise fluctuates severely.
Time/Days
Figure 5. Grease temperature rise curve in fatigue test
The analysis shows that: in the initial running-in stage of the test, the wind turbine slewing bearing has a negative clearance fit, the frictional resistance is large, and the heat generated is also large, so the temperature rise shows an increasing trend; the test reaches a stable stage after 18 days; Due to the increase in clearance and the running-in of various components, the frictional heat generation decreases, and the temperature rise tends to decrease; after 56 days, the temperature rise begins to increase again, which may be caused by the failure of the bearing raceway. Therefore, the grease temperature rise can be used as an important parameter for judging whether the slewing bearing channel is faulty.
2.2.3 Analysis of Vibration Acceleration Variation
The time-domain curve of vibration acceleration is shown in Figure 6 (g in the figure is the acceleration of gravity), the wind turbine slewing bearing is a negative clearance fit, due to the intensification of wear, the vibration is relatively large in the early stage of operation; with the mechanical running-in, the vibration amplitude decreases slowly ; When the running-in is completed, the vibration tends to be flat and the vibration amplitude tends to be stable; when the channel fails or the wear continues to increase, the vibration increases again. From the vibration acceleration envelope curve (Fig. 7), it can be seen that it is similar to the variation law of the torque, first falling and then rising.
Time/Days
Fig.6 Axial acceleration curve of fatigue test
Time/Days
Fig.7 Axial acceleration envelope of fatigue test
2.2.4 Joint judgment
The joint judgment combined with the driving friction torque, the temperature rise of the channel grease and the vibration envelope is shown in Fig. 8. It can be seen from Figure 8 that the friction torque is consistent with the inflection point of the temperature rise at 56 days, which shows that the time when the channel failure occurs can be determined by combining the trend graph of the grease temperature rise and the friction torque. In order to qualitatively and quantitatively analyze the above-mentioned experimental phenomena, an empirical model needs to be established. According to the above test data, piecewise fitting is performed, and the fitting formula of friction torque and time is:
y=0. 668x2-0. 580x+9. 684, x ∈ ( 0, 30)
y=-0. 008x + 8. 787, x ∈ (30, 45)
y=1.385x2-1.524x+12.288, x ∈ (45,76),(1)
The fitting formula of the temperature rise and time of the channel grease is:
y=0. 351x3-4. 1x2+1. 427x+16.021,(2)
The fitting curve formula of acceleration amplitude envelope and time is:
y=0. 0000013x2-0. 0001x+0. 0026.(3)
From the trend of the test data and the fitting formula, the following judgment conditions can be drawn:
At the beginning of the test (run-in stage), the slope of the friction torque curve is negative, the slope of the grease temperature rise curve is positive, and the slope of the envelope curve on the acceleration is negative;
In the middle stage of the test (stable stage), the slope of the friction torque curve is negative, the slope of the grease temperature rise curve is negative, and the slope of the envelope curve on the acceleration tends to zero;
In the later stage of the test (fault occurrence stage), the slope of the friction torque curve is positive, the slope of the grease temperature rise curve is positive, and the slope of the envelope curve on the acceleration is positive.
Time/Days
Fig.8 Joint judgment of fatigue test parameters
3 Conclusion
Through the data analysis and curve fitting of the temperature rise, friction torque and acceleration of the test bearing grease, it can be seen that when the friction torque, the fitting curve of the grease temperature rise and the first derivative of the envelope on the vibration acceleration are all positive, Indicates that the wind turbine slewing bearing channel is faulty. The joint judgment of the three has higher reliability than the single fault judgment. To make a threshold judgment, it is necessary to accumulate the results of multiple experiments to make a more accurate judgment.
4 More about VAFEM Slewing Bearings
As a precious high quality Slewing Bearings manufacturer and supplier in China, VAFEM can guarantee the quality and precision of the products through complete testing technology and advanced equipment.
Slewing Bearings are designed for large load-bearing capability and can manage a full range of heavy-duty mechanical equipment. These devices have the capacity for horizontal, vertical or inclined operations of many varied applications. Each element may be custom designed to work independently or harmonize with existing equipment.
These High-Quality Slewing Bearings are mainly used in the Excavators, Mobile Cranes, Tower Cranes, and also widely used in the Construction Machinery, Light Industry Machinery, Metallurgical Mining Machinery, Environmental Protection Machinery, Petrochemical Machinery, Engineering Vehicles, Ship Port Machinery and more gradually.
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2022-09-21