With the rapid development of the national economy, wind power, as one of the clean energy sources, has attracted increasing attention. Wind turbines are an important component of wind power generation systems, and their operation and maintenance are extremely important. The working environment of wind turbines is extremely harsh, with long-term exposure to extreme high and low temperatures, high humidity, and large dust. Most of them are located in remote areas, making maintenance inconvenient. Therefore, ensuring their long-term stable and reliable operation is a basic requirement. Wind turbines are large rotating equipment, and the importance of lubrication is self-evident.
As is well known, different lubricants need to be configured for different lubrication objects. The lubrication system of wind turbines mainly includes two parts: one is the liquid lubricating oil lubrication used for the main gearbox, yaw pitch gearbox, and hydraulic system components, and the other is the semi-solid lubricating grease lubrication used for the main shaft bearings, yaw ring gears, pitch bearings, etc.
1. Main gearbox lubrication
Except for direct drive wind turbines, other forms of turbines require the use of gearboxes, which transmit power through gear pairs. The main gearbox of the wind turbine is shown in Figure 1.
Figure 1 Main gearbox
Component composition of the main gearbox
Common gear pairs: The commonly used gear pairs in the main gearbox include spur and helical cylindrical gear pairs, and planetary gear systems.
(1) The spur and helical cylindrical gear pair consists of a pair of gears with parallel shafts. The teeth of a spur cylindrical gear are parallel to the gear shaft, while the teeth of a helical cylindrical gear are at a certain angle to the axis. The herringbone gear has two rows of inclined teeth on each gear.
(2) A planetary gear system is a gear transmission system in which one or more so-called planetary gears revolve around a sun gear and also rotate on their own. The schematic diagram is shown in Figure 2.
Figure 2 Schematic diagram of planetary gear system
In the actual application of wind turbine main gear system, the common form of Z is a mixture of planetary gear system and parallel axis gear system. The commonly used tooth profile in spur gears, helical gears, and herringbone gears is the involute tooth profile. This tooth shape means that when the base circle rotates uniformly, the tooth surface undergoes uniform displacement, and the contact line is a straight line.
Gearbox classification: There are many types of gearboxes for wind turbines, which can be traditionally classified into cylindrical gearboxes, planetary gearboxes, and gearboxes that are combined with each other; According to the number of transmission stages, it can be divided into single-stage and multi-stage gearboxes; According to the arrangement of the transmission, it can be divided into expansion type, diversion type, coaxial type, and hybrid type.
Box and bearing structure: The transmission gear pair is placed inside the box, and the box must have sufficient rigidity to withstand force and torque to prevent deformation and ensure the quality of the transmission. When producing boxes in large quantities, ductile iron and other high-strength cast iron boxes are often used, which have good vibration damping and are easy to cut. However, when producing single pieces or small batches, welding or a combination of welding and casting boxes are often used.
In order to facilitate assembly and regular inspection of the meshing status of gears, an observation window is usually provided on the box body, and a connected hook is usually installed next to the machine base for lifting the entire gearbox. In addition, the gearbox is installed on an elastic support made of high-strength rubber and steel pads to reduce the vibration transmitted by the gearbox to the engine room and machine base. The box body is also equipped with a breathable cover oil level indicator, oil injector, and oil drain hole. Cylindrical roller bearings, tapered roller bearings, self-aligning roller bearings, etc. are commonly used in gear boxes. Among all rolling bearings, self-aligning roller bearings have large bearing capacity Z, and can be widely used in supporting parts that bear large loads or are difficult to avoid coaxial errors and large deflections.
Sealing device: The sealing device at the shaft extension of the gearbox can prevent lubricating oil from leaking out on the one hand, and prevent impurities from entering the box on the other hand. There are two commonly used sealing devices: non-contact sealing and contact sealing.
(1) Non contact sealing: Commonly used are gas membrane sealing and filter membrane sealing, which can achieve zero leakage of sealing medium, completely eliminate environmental pollution, and all non-contact seals will not cause wear and tear, with a long service life.
(2) Contact seal: Contact seal is a seal that uses sealing components. The sealing components should be reliable, durable, have low friction resistance, easy to assemble and disassemble, and should be able to improve sealing ability with increasing pressure and facilitate automatic wear compensation. Lip seals are commonly used for rotating shafts.
Requirements for the operating conditions of the main gearbox lubricating oil
As the core transmission component of wind turbines, considering that the friction pair of the main gearbox has both low-speed heavy load and high-speed light load conditions, and operates in harsh environments, the lubricating oil used for it has high viscosity, extreme pressure anti-wear performance, emulsion resistance, and oxidation resistance? There are high requirements for qualitative and thermal stability, rust and corrosion resistance, and foam resistance.
Main gearbox lubricating oil monitoring indicators and cycles
(1) Essential monitoring indicators: kinematic viscosity (40 ℃), moisture content, elemental content, PQ index, infrared analysis, ferrography analysis, cleanliness, and acid value are selected as the main indicators for gearbox oil monitoring.
(2) Monitoring cycle: once a year. If the monitoring results are abnormal, re inspection will be conducted based on the oil report; The unit needs to be monitored once every three months before the warranty is issued, as one of the criteria for determining the operating status of major components during the warranty period. This monitoring can be included in the monitoring frequency specified above.
2. Yaw and pitch gearbox lubrication
The yaw mechanism is coordinated with the unit control system to rotate the engine compartment to keep the swept surface of the wind turbine perpendicular to the wind direction, ensuring that the wind turbine is always in a windward state to ensure that the wind turbine has a Z-large power generation capacity. The structure of the yaw system is shown in Figure 3 below; The pitch mechanism adjusts the angle of attack of the blade profile by changing the pitch angle of the blades installed on the hub to adapt to changes in wind speed, thereby changing the aerodynamic characteristics of the blades and greatly improving the stress conditions of the blades and the entire machine. The structure of the pitch system is shown in Figure 4.
Figure 3 Yaw system structure
Figure 4 Structure of variable pitch system
Composition of yaw and pitch gearbox components
The yaw and pitch gearbox of the wind turbine has a motor flange that can directly install the servo motor shaft. The gearbox has a four or five stage planetary transmission mechanism, each stage of which has a sun gear, planet gear, planet shaft, and planet carrier. The input shaft of the gearbox meshes with the first stage sun gear. In addition, mainstream yaw and pitch gearboxes use NGW planetary transmission, which has the advantages of high power density, compact structure, high transmission efficiency, large transmission ratio, smooth operation, strong impact and vibration resistance.
Working condition requirements for lubricating oil of yaw and pitch gearbox
Both yaw and pitch gearboxes have characteristics such as low-speed overload, frequent start stop, and high torque. The variable pitch gearbox rotates 360 degrees with the blades, experiencing greater impact and working most of the time. Theoretically, the working conditions are more severe, requiring higher reliability; The yaw gearbox only works for part of the time and is installed vertically in the engine compartment, making maintenance slightly more convenient than pitch control. However, due to abnormal working conditions such as passive yaw, the lubricating oil used for it should have high load-bearing capacity, good extreme pressure and anti-wear performance, and high viscosity. Generally, VG320 or VG220 synthetic gear oil is used.
Monitoring indicators and cycles of lubricating oil for yaw and pitch gearbox
(1) Monitoring essential indicators: kinematic viscosity, elemental content, PQ index, infrared analysis.
(2) Monitoring cycle: Before the warranty of the unit is issued, a sampling inspection of the yaw and pitch gearbox oil of the entire unit should be carried out at a ratio of 20% of the number of units. If the inspection results are not qualified, the replacement should be negotiated with the complete machine manufacturer.
3. Hydraulic system lubrication
The hydraulic system is a mechanical unit that uses pressurized liquid as a medium to achieve power transmission and motion control. It has the advantages of smooth transmission, high power density, easy stepless speed regulation, easy replacement of components, and reliable overload protection. It is widely used in large wind turbines.
In fixed pitch wind turbines, hydraulic systems are mainly used for aerodynamic braking, mechanical braking, as well as yaw drive and braking; In variable pitch wind turbines, the hydraulic system is mainly used to control the pitch mechanism and mechanical braking, as well as for yaw drive and braking. In addition, hydraulic systems are commonly used for cooling and filtering lubricating oil in gearboxes, water cooling in generators, temperature control in inverters, switching engine rooms, and driving cranes. The hydraulic system structure of wind turbines is shown in Figure 5.
Figure 5 Hydraulic System Structure of Wind Power Unit
Components composition of hydraulic system
The hydraulic system of a wind turbine is a public service system that provides power to all devices on the wind turbine that use hydraulic driving force. Its main function is to provide hydraulic driving force to the pitch control device, safety pitch control device, yaw drive and braking device, and shutdown braking device.
The hydraulic system consists of power components, control components, actuating components, and auxiliary components. Power components convert mechanical energy into hydraulic pressure energy, such as hydraulic pumps; Control components control system pressure, flow rate, direction, and perform signal conversion and amplification. As control components, various hydraulic valves are mainly used; The actuator converts the pressure energy of the fluid into mechanical energy, driving various mechanisms such as hydraulic cylinders; Auxiliary components refer to devices other than the above three components, such as fuel tanks, filters, accumulators, and fittings, to ensure the normal operation of the system.
Requirements for operating conditions of hydraulic system lubricating oil
In a fixed pitch wind turbine, the main task of the hydraulic system is to drive the pneumatic and mechanical brakes of the wind turbine; In variable pitch wind turbines, the hydraulic system mainly controls the pitch mechanism to achieve speed control and power control of the wind turbine, as well as the mechanical brake mechanism. The hydraulic oil used should have good viscosity and temperature performance, rust and corrosion resistance, cleanliness and other properties. VG32 synthetic hydraulic oil is often used.
Monitoring indicators and cycles for lubricating oil in hydraulic systems
(1) Monitoring indicators: including kinematic viscosity (40 ℃), moisture content, elemental content, PQ index, cleanliness, and infrared analysis.
(2) Monitoring cycle: Three months before the warranty of the unit is issued, all hydraulic oils of the unit need to be monitored once. For hydraulic oils that fail the inspection, they should be replaced in consultation with the complete machine manufacturer; When the usage time reaches 5 years, the hydraulic oil of all units should be inspected once, and then every two years. For abnormal cases found during the inspection process, the sampling frequency should be appropriately increased or the hydraulic oil should be replaced according to the recommendations of the oil monitoring report.
4. Conclusion
By introducing the lubrication aspects of the main gearbox, yaw pitch gearbox, and hydraulic system of wind turbines, the importance of lubrication management in the operation of wind farms is reflected. Doing a good job in lubricating oil testing, mastering the physical and chemical characteristics of lubricating oil, and being able to timely detect the wear status of major components of the unit can effectively improve the reliability of wind turbine operation.
Through the introduction of the gearbox, yaw pitch gearbox, and hydraulic system of wind turbines, reactive lubrication is of great significance for the safe and stable operation of large components of wind turbines, directly related to the reliability and power generation of wind turbine equipment. The laboratory indicators and cycles of lubricating oil during operation are also elaborated.
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