Wind turbines generally require a life span of 20 to 25 years, with varying failure rates over that life span. Wind turbines are complex machines that include electrical components, sensors, hydraulic systems, yaw motors, rotor blades, mechanical brakes, gearboxes, generators, etc. Failure of any of these components can cause downtime of varying duration.We first mainly talk about the impact of frequent start/stop and pitch bearing failure of wind turbines on the service life of wind turbines.
The failure rate is higher in the first three years. This is due to the need to address the new wind turbine model or the need to make adjustments to the operating controls. Once the initial "break-in" period is over, the turbine will usually operate reliably for the next 15 years. Thereafter, the turbine begins to wear out and the failure rate climbs.
1.The frequent start and stop of the wind turbine will have an impact on the life of the wind turbine
1.1 The shortening of the life of the inverter MCB in the wind turbine
(1) There is an upper limit to the number of times the inverter MCB operates in the wind turbine, which is generally 10,000 times.
(2) How to reduce the number of starts and stops of the wind turbine as much as possible while not affecting the normal power generation of the wind turbine?
(3) First of all, the cut-in wind speed of the wind turbine can be adjusted according to the wind condition of the wind field in the region. Most of the 1.5MW wind turbine cut-in wind speed is set at 3m/s, such as the wind field in the summer for the dry wind period, the average wind speed does not exceed 5m/s, so the cut-in wind speed of the wind turbine can be adjusted to 5m/s, so that the wind turbine will not reach the start wind speed, it can not be connected to the grid, the MCB will not act, but also to avoid the low wind speed (2m/s-5m/s) in the case of unstable wind conditions lead to frequent wind turbine .This not only does not achieve the purpose of wind power generation, but also reduces the service life of MCB.
1.2 frequent start and stop of the wind turbine on the wind turbine communication slip ring is also a certain impact
When the wind turbine is running normally, the toner inside the communication slip ring can be taken away, but with frequent start/stop, the toner impurities inside the slip ring cavity will not be blown away easily, which will lead to unclean slip ring cavity and have a certain impact on the communication channel inside the slip ring, causing the pitch communication failure.
1.3 Shortening of the life of the pitch motor
(1) summer wind turbine hub temperature is relatively high, the control wind blade open and close the propeller motor itself in a hotter temperature service, then if the low wind conditions in the frequent open and close the propeller, the start current is larger, the heat can not be timely dissipated, the motor temperature can not be lowered, the motor internal coil is the form of enameled wire, so the paint is easy to fall off in this case, resulting in coil The burn, damage to the pitch motor.
(2) The wind turbine runs all year round, the parts will fail at any time, causing the shortening of the fan life. Such as inverter, gear box, generator, pitch system, etc. are the core components of the wind turbine, only the timely maintenance of these components to extend the life of the wind turbine, which highlights the importance of routine maintenance and inspection of the wind turbine. The health of the wind turbine to do a good job, so as to prevent in advance, to achieve the real state of repair.
(3) inspection of the wind turbine is best to do a monthly cabin inspection, arrange a special person to do a detailed inspection of the cabin and tower parts, timely detection of problems, solve problems and make records.
2.Pitch bearing
2.1 About Pitch Bearings
As a core component of wind turbine, the pitch bearing directly affects the consistency, stability and accuracy of the entire pitching action. With the gradual aging of domestic wind turbines in service, coupled with extreme weather, unpredictable load fluctuations and other factors, the wind turbine pitch bearing may fail unexpectedly, resulting in a decline in the life of the wind turbine, through the design of the pitch bearing upgrade, the life of the pitch bearing can be extended by up to 10 years, extending the life of the wind turbine at the same time, to improve the operating efficiency of the wind turbine and reduce downtime.
Variable pulp is the wind turbine blade change angle process, variable pulp bearing is used for variable pulp mechanism bearing, which is located in the rotor hub and blade connection position, in the hydraulic drive can be adjusted to the blade to suit the wind conditions of the best angle, variable pulp bearing maintenance costs are high, requiring a long life.
Pitch bearings are designed for a 20-year service life (approximately 175,000 hours) and typically consist of gothic arch races with deep grooves and the largest ball balls. The ball balls are evenly distributed by disc-shaped spacers or cage separators.
Single-row, four-point or double-row, eight-point contact designs provide excellent load capacity, and the bearing raceways allow the balls to be loaded from any direction simultaneously. Ideally, the pitch bearing would never rotate more than 90° during its entire service life, but the fact that the pitch bearing is subjected to very small (<5°) oscillation angles under heavy loads can put a lot of stress on the pitch bearing components, as well as rapid degradation of the bearing lubricant due to vibration and lead to adhesive wear.
Most of the wind turbines in China are located in remote and complex environments, and the position of the pitch bearing is at the top of the wind turbine tower, so the problem cannot be found by regular inspection and observation.
2.2 Causes of Pitch Bearing Failure: Lubrication
The classical failure modes predicted by standard bearing calculation models (i.e. fatigue spalling and Brinell spalling) are not actually common causes of pitch bearing failures. Common failures are usually the result of poor lubrication. Lubrication-induced failures include vibration wear (erroneous Brinell wear), corrosion, debris settling and surface-induced fatigue. Damaged separators, stripped races, split balls and locked bearings can all be signs of poor lubrication in pitch bearings. Many of the failures classified as load-based may actually be due to problems caused by grease degradation.
Because wind turbines are subjected to harsh weather conditions, proper lubrication methods must be designed to ensure maximum machine uptime and minimal maintenance. Proper grease selection is the first and most important step. Pitch bearing grease must be resistant to water washout and contain a durable additive package that protects against high loads and vibration. Using a continuous feed lubrication system also allows grease fill to be added or adjusted as needed in the field without the need for technicians to climb.
2.3 Causes of Pitch Bearing Failure: Overload Operation
Although lubrication is the primary cause, overload operation failures are also an area of concern. Overloads usually occur because the bearing lacks the rigid support of the hub assembly, resulting in an imbalance in which a portion of the raceway carries most of the load. Load and operation induced failures include component rupture (rolling ball elements, ball separators, seating), separator lock-up and raceway core breakage. As mentioned above, lubrication conditions can also exacerbate these failures.
In a pitch bearing, the contact area between the ball and raceway forms an ellipse that is centered on the raceway contact angle. Under higher thrust or overturning loads, the contact ellipse can overflow the physical limits of the raceway (truncation). The likelihood of contact truncation increases with the ratio of bearing diameter to thickness, or with the reduction of external support.
Severe contact truncation produces a stress rise that can lead to path edge fracture or ball splitting into fragments. Finally, the calculation relies on a set of conditional assumptions that sometimes bear little resemblance to real life. Bearings with new seals, fresh grease and mounted on a solid, perfectly flat surface in a clean room may last for decades.
2.4 Pitch bearing upgrade method
(1) Increase the path surface area and strengthen the seat ring
(2) Separating ring and raceway geometry
(3) Seal upgrade
(4) Improve raceway durability
(5) Proper storage, packaging and handling
(6) Customized solutions to extend fan life
2.5 Benefits of Pitch Bearing Upgrades
(1) Improved wind turbine reliability even in harsh environments
(2) Extended seal and bearing life
(3) Reduced operation and maintenance costs
(4) Improved pitch control for better performance
In order to optimize turbine performance, operators must perform planned and unplanned maintenance. Multiple departments are set up to monitor the status of the turbines in all aspects, and to identify problems for timely maintenance and upgrades to extend the life of the wind turbines as much as possible and thus create better benefits.
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