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Determination of fault characteristic parameters of wind power turntable bearing

Wind power generation equipment is expensive, with harsh operating environment and high disassembly cost. Once there is a failure, huge claims may be generated, so the wind power generator group should seek life of no less than 20 years and the warranty period of 5 years [1]. Wheel bearing in the process of design, manufacture, installation and use can produce all kinds of fault, including: rolling element and raceway pitting wear which resulted in increased clearance, oil free dry friction, maintains a fracture, rolling element and raceway serious abrasion and potholes, inner and outer ring and the upper and lower connection of metal structure is loose, metal structure, cracks, etc. [2]. These faults can be shown by vibration. In the actual use process, there will be some problems such as the temperature of raceway grease increasing and the power of driving motor increasing. However, due to the low speed (1-26 r/min) and large bearing capacity (the mass of blades and engine room reaches more than ten tons) of wind power rotary table bearings, they are not sensitive to the vibration generated, and some faults are not easy to be found [3].

At present, the problems facing the fault diagnosis of wind turbine rotary table bearing are [4] : (1) the bearing speed is very low, and the calculated fault frequency is very low. The high-pass filter will filter out the frequency below 3 Hz, coupled with the influence of environmental noise, so that the spectrum analysis effect is very poor or even impossible to carry out; (2) The interval of each fault impact is long, and it is difficult to detect the fault signal accurately by using the impact method; (3) The impact response frequency generated by the fault point is low, and the higher frequency component cannot be excited.

Wind turbine rotary table bearings usually only make small amplitude reciprocating rotation, many occasions for a long time in a static state, while bearing complex alternating load. Therefore, its failure mechanism is different from the rolling contact fatigue of ordinary bearings, and the design theory of ordinary bearings cannot solve the design and quality problems of rotary table bearings very well [5]. The experience of fault diagnosis is very little. Therefore, how to solve this problem has become a hot research topic in many countries. According to the literature [6-10], the world’s major famous enterprises have their own laboratories and test equipment, but they are always in the stage of technical blockade, and only publish partial pictures related to tests in advertisements or websites. Literature [11-12] studies the relationship between average friction torque, raceway wear and life. In reference [13], the fault diagnosis and test study of port turntable bearing are carried out. In reference [14-15], low speed and heavy load rotary table bearings of steel rolling were studied, and stress wave and wavelet analysis were used for fault diagnosis. On the basis of years of experimental research, literature [16-17] studies the bearing stiffness, raceway wear, starting torque, fatigue life and tooth root strength of wind power rotary table bearings, and considers that the main parameters for fault diagnosis and detection of wind power rotary table bearings are as follows: The number of running laps of the bearing, raceway wear, vibration acceleration, friction torque, raceway crack, grease temperature and driving motor power, etc. However, the parameter indexes characterizing the performance characteristics of wind turbine rotary table bearing still need to be deeply discussed in combination with tests.

Bearing fatigue life test

1.1 Test device

The comprehensive performance test device of wind turbine rotary table bearing is composed of mechanical part, hydraulic system and measurement and control system. The test device is loaded by the hydraulic cylinder, and the axial force, radial force and overturning moment can be applied to the bearing at the same time. The hydraulic motor drives the turntable bearing to rotate and simulates the actual running state of the bearing. At the same time, the data is collected by the test sensor, and stored and processed.

1. 2 Detection Parameters

Once the rotor bearing fails, its vibration, temperature, friction torque, noise and tooth root stress will change. Through the corresponding signal processing technology, the useful characteristic parameters can be extracted from the complex signal, which can characterize the running condition of the bearing, and the diagnosis of the turntable bearing can be realized by analyzing these characteristic parameters.

Friction torque can reflect the working performance, power consumption, life and safety performance of wind turbine rotary table bearing, which is mainly derived from the contact friction resistance between rolling body and raceway. Generally, friction torque is mainly caused by applied load [18]. When the turntable bearing is faulty, the running resistance will increase. In view of the randomness and complexity of the friction torque of the rotary table bearing, it is difficult to obtain the exact value by the method of theoretical analysis. Therefore, the friction torque of the rotary table bearing can be measured by the test, and the

Evaluate bearing performance and running condition.

Under normal circumstances, the friction of the rotary table bearing consumes energy in the form of heating, and the friction temperature rise of the rotary table bearing is comprehensively affected by the heat generated by each moving pair and the room temperature [19]. When the rotary table bearing starts to run, due to the rise of the friction running temperature, after running for a period of time, the temperature balance is reached, and the change of raceway temperature remains relatively constant with the environment temperature. When the raceway spalling, iron debris mixed with grease, ball and channel wear, resulting in the increase of bearing friction torque, causing heat, so that the rotary bearing temperature rise further increases. Temperature rise will easily lead to local burns of bearing parts, damage of lubrication film, and aggravate bearing wear. Therefore, it is very necessary to monitor the temperature of the rotary table bearing.

Vibration analysis of the rotary table bearing is the most effective diagnostic method [20-21]. According to previous test results [16-17], the vibration direction of the rotary table bearing is located in its axial direction, close to the driving motor. The temperature rise, friction torque and vibration acceleration of the wind turbine rotor bearing were measured in order to study the parameters characterizing the operation of the rotor bearing. The sensor layout of the test device is shown in FIG. 2, where the temperature sensor is placed in the mounting hole and contacts with the grease.

1. 3 Test bearing parameters

For a company 033. 50. The speed life test of 2410 type wind turbine rotary table bearing was carried out. The test bearing parameters were as follows: channel center diameter 2410 mm, steel ball diameter 50 mm, ball number 140, contact Angle 45°, outer tooth number 135. The bearing is a double-row four-point contact ball bearing, the outer ring is a gear ring, the material is 42CrMo, the steel ball material is GCr15. When the number of stress cycles reaches 1 million times, the theoretical fatigue limit of the material is reached, and the maximum speed of the turntable bearing in the test is 1. 5 r/min, 50% full load, the test runs 71. 6 days.

2 Test results and analysis

2. 1 Fault Characteristics

After the test, the rotary table bearing was decompressed to check the damage of the ball and the channel. The soft belt of the inner and outer ring appeared peeling, the surface of the other channels was smooth, there was a small amount of slight indentation in the local area, no pitting corrosion and other damage phenomena, and the ball was not damaged. Groove morphology of rotary table bearing.

2. 2 Detection parameter analysis

  1. 2. The variation rule of friction torque of test bearing is shown in FIG. 4. According to the analysis of the fitted curve, the wind turbine rotor bearing has a negative clearance fit at the beginning of operation, and the friction resistance is maximum at this time. With the running in between components, the clearance increases and the friction torque decreases correspondingly. The friction torque reaches the minimum at 56 days, only 8. 096 kN · m. With the pitting of the soft belt in the channel due to wear, the iron filings enter the grease, leading to the increase of friction and the rise of friction torque. Therefore, the friction torque can be used as an effective parameter to judge the wear condition of the raceway of the turntable bearing. In order to make real-time judgment, it is necessary to establish mathematical model for quantitative judgment.

3.2. 2. Analysis of temperature rise of grease

The variation trend of grease temperature rise and its fitting curve are shown in FIG. 5. It can be seen from FIG. 5 that the fluctuation of temperature rise is serious.

The analysis shows that: in the initial stage of the test, the wind turbine rotor bearing has a negative clearance fit, and the friction resistance is large, and the heat generated is large, so the temperature rise shows an increasing trend. The experiment reached a stable stage on the 18th day. After 30 days of the test, the friction heat generation decreases and the temperature rise decreases due to the increase of clearance and the running-in of each component. After 56 days, the temperature rise began to increase again, which may be caused by bearing groove failure. Therefore, the temperature rise of grease can be used as an important parameter to judge whether the turntable bearing channel is faulty.

2.2. 3. Analysis of vibration acceleration change

The time-domain curve of vibration acceleration is shown in FIG. 6 (g is the gravity acceleration in the figure). The wind turbine rotary table bearing has a negative clearance fit, and the vibration is relatively large at the early stage of operation due to the aggravation of wear. The vibration amplitude decreases slowly with mechanical running-in. When the run-in is completed, the vibration tends to be gentle and the vibration amplitude tends to be stable. When the channel fails or the wear continues, the vibration increases again. As can be seen from the vibration acceleration envelope curve (FIG. 7), it is similar to the change law of torque, which decreases first and then rises.

2. 2. 4 Joint judgment

The joint judgment of driving friction torque, channel grease temperature rise and vibration envelope is shown in FIG. 8. It can be seen from FIG. 8 that the inflection point of friction torque and temperature rising at 56 days is consistent, indicating that the time of channel failure can be determined by combining the trend diagram of grease temperature rise and friction torque.

The following judgment conditions can be obtained from the trend of test data and the fitting formula:

At the initial stage of the test (running-in stage), the slope of the friction torque curve is negative, the slope of the temperature rise curve of the grease is positive, and the envelope of the acceleration is oblique

Rate is negative; The slope of the friction torque curve and the temperature rise curve of the grease are negative and the slope of the envelope curve on the acceleration tends to zero in the middle (stationary phase) of the test.

The slope of the friction torque curve at the later stage of the test (failure stage) is positive, the slope of the grease temperature rise curve is positive, and the slope of the envelope on the acceleration is positive.

conclusion

Based on the data analysis and curve fitting of the temperature rise, friction torque and acceleration of the test bearing, it can be seen that when the fitting curve of the friction torque, temperature rise of the grease and the first derivative of the envelope on the vibration acceleration are positive, it indicates that the wind power turntable bearing channel is out of order. The combined judgment of the three factors has higher reliability than that of single fault determination. If the threshold is to be judged, it is necessary to accumulate the results of several tests to make a more accurate judgment

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