Figure 1 Fault Distribution Caused by Fan Components
Fault distribution caused by different parts in wind turbine.
Fig. 2 downtime caused by failure of fan components.
Downtime caused by different parts and components in wind turbines
1 ? blade
Blade (blade) is the core component of wind turbine to capture wind energy, and its working environment is harsh. Even when the fan works normally, the blades often bear high stress, which is prone to the following faults: due to pollution, peeling and other reasons, the surface roughness of the blades increases; Due to the loose structure, the material in the blade moves and the rain enters the blade through cracks, which leads to the imbalance of the blade. Blade deformation, pitch control failure and other reasons cause aerodynamic imbalance of blades; Faults such as cracks on the blade surface or internal structure caused by fatigue and lightning strike.
When the blade is cracked or deformed, it will release high frequency (generally 1 kHz ~ 1 MHz), time-varying, non-stationary and transient acoustic emission signals. Therefore, acoustic emission detection has been successfully applied to the detection and evaluation of blade damage. Due to the failure of blades, the rotor blades are unevenly stressed, and these stresses will eventually act on the engine room through the transmission of the main shaft, which is easy to cause the engine room to shake. Caselitz P et al. collected low-frequency (0. 1 ~ 10 Hz) vibration signals by installing multiple vibration sensors on the spindle, and successfully analyzed the faults such as unbalanced blade rotation by using the algorithm.
2 gearbox
Gear box is a transmission component connecting the main shaft of the fan and the generator, and its function is to increase the low speed on the main shaft to a relatively high speed to meet the speed requirements of the generator. Gearbox is generally composed of one-stage planetary gear and two-stage parallel gear transmission, which has harsh working conditions, complex working conditions and high transmission power. Planetary gears, high-speed shaft side bearings, intermediate shaft bearings, planetary gear transmission side bearings and their lubrication systems in gear boxes are prone to failure. During the operation of wind turbine, due to the action of alternating stress and impact load, gears are prone to tooth surface wear, tooth surface scratch, pitting and tooth breakage. Bearings are prone to wear, raceway slip, roller slip, outer ring deviation and other faults. Although gearbox is not the most common component of wind turbine, the downtime and maintenance time caused by gearbox failure is the longest and the maintenance cost is very high. Therefore, the fault diagnosis and prediction of gearbox has been widely concerned. Huang Q and others successfully diagnosed the gearbox fault by analyzing the vibration signal of gearbox and using wavelet neural network method. In addition, analysis methods based on information such as bearing temperature, lubricating oil temperature and oil abrasive particles have also been proposed for gearbox fault detection.
3 Motor (generator or motor)
Doubly-fed generator and permanent magnet synchronous generator are widely used in current wind turbine technology. Among them, the speed of doubly-fed wind turbine is relatively high, and its rated speed is 1 500 r /min. Therefore, a gearbox is needed in the turbine to increase the speed, which makes the turbine heavier and the generator runs at high speed with certain noise pollution. The motor is an asynchronous generator, the converter is connected to the rotor, and the power of the converter can flow in both directions. Variable speed and constant frequency operation is realized by AC excitation adjustment of the rotor. The operating range of the unit is very wide, and good power output can be obtained in the range of 60% ~ 1 10% of the rated speed.
Direct-driven wind turbine is directly coupled with the rotor of the motor through the wind wheel, and the speed of the motor is low, generally tens of revolutions per minute. Direct-driven wind turbines generally use permanent magnet synchronous motors, which have large starting torque. The stator winding is connected to the power grid through a full-power converter, and the working range of the turbine is very wide. However, the generator has complex structure, large diameter and high cost. In addition to generators, motors are also widely used in yaw and pitch control systems of wind turbines.
Motor faults are usually divided into electrical faults and mechanical faults. Electrical faults include winding short circuit, open circuit, overheating, three-phase imbalance and so on. Mechanical failures include overheating and damage of bearings, abnormal air gap between stator and rotor, wear and deformation of rotating shaft, etc. Through the analysis of signals such as vibration, current and temperature, the motor fault can be detected.
4 Yaw, pitch and braking system
The yaw system has two main functions:
1) make the wind turbine follow the wind direction;
2) Because it is easy to wind the cables from the engine room by tracking the wind direction, the yaw system can be used to solve the problem of cable winding when the wind is too strong.
The function of pitch control system is to change the torque of wind turbine by controlling the angle of blades when the wind speed changes, so as to obtain aerodynamic force and realize power control. When the wind speed is too high or the fan fails, adjust the blades to the feathering state to realize braking. Yaw and pitch systems work frequently, and the yaw and pitch bearings bear large torque. The yaw bearings are partially exposed to the environment and are easily damaged by dust and salt (water) fog corrosion. Due to its working characteristics of incomplete rotation, pitch bearings are prone to poor lubrication, leading to bearing wear and other failures. The braking system is used to prevent the rotor blades from rotating too fast and stop the wind turbine when other parts of the wind turbine fail. Due to the wear of friction plates and excessive stress, the braking system is also prone to failure. Hydraulic system has excellent characteristics such as small unit volume, good dynamic response, large transmission force and large torque, which plays an important role in yaw, pitch control and braking system of wind turbine. Hydraulic circuits interfere with each other, which makes its failure mechanism complex and failure modes diverse. Common faults of hydraulic system include hydraulic oil pollution, oil leakage, electromagnetic valve, overflow valve fault, hydraulic pump fault, oil overheating, abnormal vibration and noise.
5 converters and transformers
With the increase of single capacity of wind turbine, it is becoming more and more important whether the electrical system can run reliably. According to statistics, the electrical system is the subsystem with the highest failure rate in the wind turbine, and the electrical system failure accounts for about 20% of all failures of the wind turbine. Although the downtime of the fan caused by electrical failure is not long, the frequent failure of the electrical system will also lead to high maintenance costs. With the further improvement of wind turbine capacity, the fault frequency of electrical system will also increase.
The failure of electrical system usually refers to the failure of electronic components such as capacitors, printed circuit boards or power semiconductor devices (such as MOSFET and IGBT) due to overvoltage, overcurrent, overheating, vibration and excessive humidity. Their faults account for 30%, 26% and 265,438+0% of electrical system component faults respectively.
6 control systems and sensors
The control system of wind turbine plays an important role in yaw, pitch, cable laying and protection. Control systems usually include various sensors, controllers and actuators. Sensors collect various signals and send them to the controller for analysis, processing and logical operation. The actuator controls and protects the subsystem of the wind turbine to ensure that the wind turbine works in a safe, reliable and optimized state.
Various sensors are installed in the wind turbine, such as anemometer, wind vane, speed decoder, position encoder, temperature sensor, pressure sensor, vibration sensor and yaw sensor. Due to the harsh working environment, the sensor failure rate is high. Statistics show that more than 14% and more than 40% of the faults of wind turbine are caused by the faults of the sensor itself and the sensor-related system respectively.
Besides sensors, other faults of control system can be divided into hardware faults and software faults. Hardware faults include control board circuit faults and servo mechanism faults. Software failures are characterized by occasional system crashes and inactivity, which are usually caused by unreasonable design and memory overflow. This fault can be eliminated by restarting the control system and other actions.