2023 February the Second Week KYOCM Technical Knowledge: Application analysis of wind energy gearbox bearing

At present, the wind power gearbox is a very important part of the whole wind turbine. Due to the impact of variable load and strong gust all the year round, it is different from the ordinary gearbox in manufacturing, design and maintenance. The application practice at home and abroad shows that the bearing is one of the weakest links in all parts of the wind power gearbox. Therefore, the necessary application analysis of the bearing is an important means to ensure the reliability of the gearbox.

1. Analysis of bearing lubrication of wind power gearbox

As we all know, the rotational speed of the input shaft of the wind power gearbox is generally 10-20 rpm. Due to the relatively low rotational speed, it is often difficult to form the oil film of the input shaft bearing, that is, the planetary carrier support bearing. The function of the oil film is to separate the two metal contact surfaces during the bearing operation to avoid direct contact between metal and metal. We can introduce a parameter λ To characterize the lubrication effect of the bearing（ λ It is defined as the ratio of oil film thickness to the sum of two contact surface roughness). If λ If it is greater than 1, it means that the thickness of the oil film is enough to separate the two metal surfaces, and the lubrication effect is good; And if λ If it is less than 1, the thickness of the oil film is not enough to completely separate the two metal surfaces, and the lubrication effect is not ideal. Since the wind power gearbox generally uses ISOVG320 viscosity circulating lubricating oil, if it is found that λ If it is less than 1, we can only improve the lubrication effect by reducing the roughness of the bearing raceway and roller. In addition, in the design of the gearbox, the planetary carrier support bearing should try to avoid the size of the bearing at one end being too small. In the actual application analysis, we found that even if the life meets the conditions, this design will lead to very low linear speed of the small bearing, and the oil film cannot be formed even more.

2. Analysis of Bearing Bearing Bearing Area of Wind Power Gearbox

In general, only part of the rollers of the running bearing bear the load at the same time, and the area where the rollers are located is called the bearing bearing area. The size of the load bearing bears and the size of the running clearance will affect the bearing area. If the load bearing area is too small, the roller is prone to slip in actual operation. For the wind power gearbox, if the design of the main shaft adopts the scheme of double bearing support, theoretically only the torque is transmitted to the gearbox. In this case, after a simple stress analysis, it is not difficult to find that the load of the planet carrier support bearing is relatively small, so the bearing bearing area is often small, and the roller is prone to slip. At present, in the design of wind power gearbox, two single-row tapered bearings or two full-roller cylindrical bearings are generally used for the planetary support bearings. We can improve the bearing area by properly preloading the tapered roller bearing or reducing the clearance of the cylindrical roller bearing.

In addition, the analysis of the bearing area can help us understand whether there is only one bearing row of the double-row bearing. At present, many wind power gearbox manufacturers adopt the scheme of tapered roller bearing plus cylindrical roller bearing on the high-speed shaft, which solves the problem of pitting and peeling of the ball bearing in the traditional scheme of ball bearing plus cylindrical roller bearing, but this scheme must pay attention to a problem, that is, to avoid the phenomenon of single-row bearing of double-row tapered roller bearing. The single-row load bearing of double-row tapered roller bearing is very harmful: on the one hand, the actual load bearing capacity of the bearing is greatly reduced, resulting in a sharp reduction in fatigue life, and on the other hand, the non-stressed row of rollers is easy to slip. Through the analysis of the bearing area, we can know whether the selected double-row tapered roller bearing has the problem of single-row bearing, and we can take targeted measures. The speed of the high-speed shaft of the wind power gearbox is generally 1100-2000 rpm. Due to the high speed, the selected clearance value of the bearing is generally larger than that of the bearings at other positions, but the large clearance is also easy to cause the single-row bearing.

If it is found that the phenomenon of single-row bearing does exist, it can be considered to use tapered bearings with different taper angles in pairs. In a word, the analysis of bearing bearing bearing area can help us better understand the operation status of bearings, so as to optimize the selection of bearings and improve the design of gear box.

3. Stress analysis of bearing of wind power gearbox

One of the biggest characteristics of the wind power gearbox that is different from the ordinary gearbox is the irregularity of the load it bears. Taking the 1.5MW gear box currently popular in China as an example, the general nominal power value is 1660KW, but the maximum power value in the load spectrum can generally reach about 5000KW, about three times the nominal power value. The maximum reverse power value can generally reach about twice the nominal power value, and they are often used to check the safety static load factor. When the power value is far greater than the nominal power value, the probability of bearing stress concentration will greatly increase, which is particularly prominent in the low-speed intermediate shaft. The reason is that the low-speed intermediate shaft generally uses hollow shaft, which has relatively poor stiffness and is prone to eccentric, while eccentric can aggravate the occurrence of stress concentration.

In view of the application characteristics of the wind power gearbox, the above mainly introduces several key points that must be paid attention to in the selection and analysis of the wind power gearbox bearing from the bearing bearing bearing area, lubrication, stress concentration and other aspects, hoping to avoid some of the problems mentioned above, so as to improve the reliability of the wind power gearbox and reduce the downtime of the wind turbine.

More about KYOCM Combined Bearing：

Composite bearing is a kind of roller bearing which can bear both radial load and axial load. The structure of the combined bearing is axial and radial bearing running at 900 °, the main load is borne by the radial bearing, and the axial bearing bears the lateral thrust.

Combination bearing is used together with profile guide rail or channel steel. There are two main types of profiles, I and C profiles. The combined bearing slides into the profile guide rail to generate the required linear movement. The combined bearing is welded with the flange plate for installation according to the application requirements. The assembly is mainly used for precise heavy vertical and horizontal movement.

https://www.kyocm.com/products/Combined-Bearing/743.html

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