Wind power gearbox: structure, type and damage type popular science

In the field of wind power, the wind power gearbox is a vital component. It converts the low-speed and high-torque power generated by the wind rotor under the action of wind into the high-speed and low-torque power required by the generator, thereby driving the generator to generate electricity.

1.Structure of wind power gearbox

The wind power gearbox is mainly composed of an input shaft, an output shaft, a gear set and a lubrication system. The input shaft is the part that transmits the low-speed rotational motion of the wind rotor to the gear set. It is usually made of high-strength alloy steel to withstand the requirements of high torque and high-speed motion. The output shaft is responsible for transmitting the high-speed motion of the gear set to the generator.

The gear set is the core part of the wind power gearbox. It consists of multiple gears and realizes the transmission effect through the meshing between the gears. Gears are generally made of alloy steel to withstand high loads and high-speed working requirements. Common gear sets include main shaft gears, intermediate gears and output gears. The main shaft gears are connected to the input shaft, the intermediate gears connect the main shaft gears and the output gears, and the output gears are connected to the output shaft.

The lubrication system is an important part of ensuring the normal operation of the gear set. It usually consists of an oil tank, an oil pump, an oil pipe and a filtration system. The lubricating oil is transported to the moving parts of the gear set through the oil pump to play a role in lubrication and friction reduction. It can also cool the gear set and maintain its normal working temperature.

2.Types of wind power gearboxes

According to the traditional type, wind power gearboxes can be divided into cylindrical gear speed increasers, planetary speed increasers and combined gearboxes.

The cylindrical gear speed increaser has a simple structure and is suitable for parallel shaft transmission. Its advantages are relatively mature manufacturing technology and low cost, but the transmission load capacity is relatively weak, the structure is relatively long, and there are more large shells required for casting.

The planetary speed increaser has the advantages of high load capacity and compact structure and transmits power through the planetary gear train. It can divert power and reasonably apply internal meshing to make power distribution more reasonable and improve transmission efficiency. However, the manufacturing precision requirements of the planetary speed increaser are high, and the structure is complex.

The combined gearbox combines the design of the planetary stage and the cylindrical gear stage, taking into account high transmission efficiency and space optimization. This type of gearbox has both the high load-bearing capacity and compact structure of the planetary speed increaser and takes advantage of the simple structure of the cylindrical gear speed increaser. It is a common type.

3.Types of damage that may occur in wind power gearboxes

Gear damage
Gear damage is one of the common faults of wind power gearboxes, mainly including micro pitting, bonding, static indentation and broken teeth.

Micro pitting mainly forms some dark spots on the surface of the gear, which are actually tiny dents. The cause of its formation is related to the roughness of the gear surface and the thickness of the oil film, such as frequency load, speed change, tooth surface roughness, oil cleanliness, tooth surface hardness, etc. Preventive measures include keeping the lubricating oil cool, clean and water content, monitoring the quality and particle size of the lubricating oil, and monitoring the vibration and load changes of the gearbox.

Bonding is the formation of some fine stripe-like traces on the gear surface, which is consistent with the sliding direction of the gear teeth and occurs on the tooth surface. The main cause is the high-speed heavy load between the tooth surfaces, which leads to a rapid increase in the temperature of the tooth surface, as well as lubrication failure and insufficient hardness of the tooth surface. The preventive measures are similar to those for micropitting, and lubrication should be ensured at the beginning of meshing.

Static indentation is a fine mark formed on the tooth surface, which is a contact corrosion. After a long period of shutdown, meshing will often occur between the two teeth of the gear part, resulting in static indentation. The preventive measure is that in the case of a long-term shutdown, the wind turbine must be idled within a certain period to ensure sufficient lubrication and convert the contact surface.

Broken teeth are a very serious type of gear damage. The causes include insufficient hardness of the tooth surface, continuous operation of ultra-high load, and hard objects falling between the tooth surfaces. Broken teeth can only be repaired by replacing gears.

Bearing damage mainly occurs on the ball of the bearing and the raceway of the bearing, which is manifested as severe wear, static indentation and corrosion of the ball. The main causes are insufficient lubrication, exceeding the limit load, poor solubility when changing different types of lubricants, and long-term shutdown and storage. The preventive and maintenance measures are to ensure sufficient lubrication, ensure the quality of the lubricant, and conduct oil inspections on schedule.

The main features of a cracked case are the gear ring and housing. The causes include large impact load on the gearbox, excessive vertical axial load of the fan, and material problems of the gearbox case. The prevention and maintenance methods are to regularly check the condition of the gearbox. If the case cracks, the machine needs to be shut down immediately.

Rust mainly exists on the outside or inside of the gearbox. The causes are paint peeling off the outside of the case, long-term storage of the gearbox, and improper maintenance. It may also be caused by damage to the anti-rust oil film of the internal parts of the case. The prevention and repair methods are to check the case and internal conditions of the gearbox regularly. If rust occurs on the outside, it is necessary to repaint and remove the rust. If rust is found inside, it can be polished.

There are many reasons for oil leakage, mainly manifested as penetration at the joint of the gear ring and the case, leakage of the high-speed shaft and the low-speed shaft, and leakage of the lubrication and cooling system pipelines. For example, loose bolts of the gear ring and the case, wear of the sealing strip, wear of the packing, etc., may all lead to blockage of the oil return hole. The preventive and maintenance measures are to replace the air filter regularly, regularly check the condition of the gearbox where oil is prone to leak and the damage to the rubber strips in the sealing parts, and ensure that there is no problem with the selected model.

The damage to the connecting bolts mainly occurs at the connection between the box body and the gear ring, and the main form of damage is bolt breakage. The main influencing factors are the impact load on the gearbox, the quality of the bolts themselves, and whether the bolts are loose or not tightened according to the specified torque. The preventive and maintenance measures are to check the condition of the bolts of the gearbox, tighten them according to the specified torque when assembling the bolts, and if the bolts are deformed or broken, they must be shut down immediately.

Damage to the mechanical pump
The function of the mechanical pump in the gearbox is to apply lubricating oil to each bearing part, which is generally located at the high-speed end. The operation belongs to high-speed operation, so it is also prone to problems. The damage characteristics of the mechanical pump are generally rust and breakage of the gears. The cause of the formation is due to long-term storage, no anti-rust treatment, or damage to other parts. The prevention and maintenance method is that the high-speed shaft needs to be rotated regularly for long-term storage. If the mechanical pump is replaced, it can be done in the cabin. If the mechanical pump is running abnormally, it needs to be shut down immediately.

Abnormal noise and vibration
If there is a problem in the gearbox, it is most likely to be manifested through abnormal noise and vibration. Once the gearbox is found to have abnormal noise and vibration, it needs to be inspected and repaired in time to avoid further expansion of the fault.

Abnormal oil temperature and oil pressure are mainly manifested in high gearbox oil temperature, high or low oil pressure, etc. The main factors for high gearbox oil temperature are insufficient cooler cooling capacity design, improper main engine room ventilation structure design, lubrication system temperature control valve failure, etc. The factors affecting the abnormal gearbox lubrication oil pressure include lubrication system branch failure, lubrication system failure, etc.