1. The main functions of the hydraulic system of wind turbines are: ① driving the hydraulic mechanism to work, such as driving the action of the blade tip spoiler in a stall type fixed pitch unit. ② Shafting braking: The following diagram shows a typical hydraulic device of a wind turbine. The coarse filter at the self suction port of the oil pump sucks in hydraulic oil, which is then filtered by the fine filter and sent into the working oil circuit. The pressure of the system is determined by the overflow valve.
2. The hydraulic system of a fixed pitch wind turbine generator set: mainly introduces its air braking mechanism. The air brake mechanism is a device that uses the resistance of air to stop the operation of the wind wheel of the unit, also known as the pneumatic brake mechanism. It is composed of a pneumatic spoiler installed at the blade tip connected to the piston rod of the hydraulic cylinder at the root of the blade through a steel wire rope. The blade tip spoiler is the main brake of this type of wind turbine, and it plays a major role when braking each time.
3. The hydraulic system of hydraulic variable pitch wind turbines: The control component in the system is a proportional directional valve.
① Proportional control technology: Proportional control technology is a transitional technology between switch control technology and servo control technology. It has the characteristics of simple control principle, high control accuracy, and moderate price, and is widely used. Proportional valve is a type of hydraulic valve that replaces ordinary electromagnets with proportional electromagnets to control the movement of the valve core, thereby achieving continuous adjustment of hydraulic system pressure, flow rate, and direction. By using a proportional amplifier to control the proportional electromagnet, continuous control of the control valve can be achieved. A. Slope generator: It is a device set up to control the movement speed of the valve core and ultimately control the operating speed and acceleration of executing components such as hydraulic cylinders.
② The hydraulic pump station is composed of hydraulic pump units, oil tanks, filters, and other components. The hydraulic pump group includes components such as electric motors, hydraulic pumps, and pipelines. The oil temperature inside the tank is measured by a sensor (PT100) installed on the top of the tank.
③ The pitch control of the variable pitch control system is achieved through a proportional valve. The speed of emergency feathering is controlled by a throttle valve and limited to approximately 9 °/s.
④ Speed test (this test is usually only conducted during the prototype development phase). The purpose of the flying test is to set or verify the sudden opening valve in the hydraulic system. The high-speed test is conducted according to the following procedure: a. Change the setting values of all overspeed protections to twice the normal setting values to prevent these protections from acting first. b. Adjust the grid connected speed of the generator to 5000r/min. c. After adjusting the sudden opening valve, start the wind turbine generator set. When the speed of the wind turbine reaches 125% of the rated speed, the sudden opening valve will open and release the pressure oil in the pneumatic brake cylinder, causing the aerodynamic brake to act, causing the wind turbine speed to rapidly decrease. d. Read the maximum rotor speed and wind speed values. e. When the test results are normal, change the speed setting to the normal value.
⑤ Variable pitch system test. The hydraulic variable pitch system test mainly tests the relationship between its variable pitch rate, position feedback signal, and control voltage.
⑥ Hydraulic oil: The hydraulic oil used in the hydraulic system of wind turbines requires good viscosity temperature performance, anti-corrosion and rust prevention performance, and excellent low-temperature performance to adapt to the cold climate in the north. It is recommended to use hydraulic oils with high viscosity index, good wear resistance, corrosion resistance, oxidation resistance, air release, water separation performance, and excellent low-temperature performance. The low temperature performance, viscosity index, and other indicators of ordinary HM anti wear hydraulic oil cannot meet the usage requirements, and PAO (polymer based) should be used instead α Olefin) synthetic oil based anti wear hydraulic oil. Synthetic hydraulic oil provides excellent wear resistance protection, high and low temperature performance, and long service life.
4. Pollution and Control of Hydraulic Oil
According to statistics, faults caused by oil pollution account for over 75% of the total faults, indicating that in order to ensure the sensitivity, stability, and reliability of hydraulic systems, it is necessary to control oil pollution.
① Causes of hydraulic oil pollution: latent pollution; Invasive pollution; Internally generated pollution; Lack of strict management.
② The hazards of hydraulic oil contamination. Oil pollution can reduce the sensitivity, stability, and reliability of the system, and shorten the service life of hydraulic components. The specific manifestations include: a. pollutants cause blockage of the throttle orifice and the damping hole of the pressure control valve, causing unstable system pressure and speed, and insensitive action. b. Contaminants can cause increased wear and tear of hydraulic components, increased internal leakage, and shortened service life. c. Contaminants can accelerate the damage of sealing components, causing damage to the surface of the oil cylinder or piston rod, leading to increased leakage in the hydraulic cylinder; d. Contaminants can jam the valve core, causing the valve to malfunction and cause malfunction. e. Pollutants can clog the filter, making it difficult for the pump to absorb oil, causing cavitation and increasing noise. f. Pollutants can accelerate the oxidation rate of the oil and decrease its lubrication performance.
③ Measures to control hydraulic oil pollution: a. Control the working temperature of hydraulic oil; b. Reasonable selection of filter accuracy; c. Strengthen on-site management.
⑤ Strengthening on-site management is an effective measure to prevent hydraulic system pollution. The main projects are as follows: a. Establish a hydraulic system maintenance system; b. Regularly check the cleanliness of the oil and sample the oil for testing; c. When checking the cleanliness of the equipment, the cleanliness of the hydraulic system oil, oil tank, and filter should be checked at the same time. If oil pollution exceeds the standard, the oil or filter should be replaced in a timely manner; d. Regularly clean the filter element, oil tank, pipelines, and dirt inside the components; e. Properly handle the oil.
5. Inspection and maintenance of hydraulic system
1) Inspection items for hydraulic system: ① Check for external leaks at hydraulic valves, hydraulic cylinders, and pipe joints. ② Is there any abnormal noise during the operation of the hydraulic pump? ③ Whether the full stroke movement of the hydraulic cylinder is normal and stable; ④ Is the pressure at each pressure measuring point of the hydraulic system within the specified range and stable? ⑤ Is the oil temperature in the hydraulic system within the allowable range? ⑥ Is the directional valve sensitive and reliable in operation? ⑦ Is the amount of oil in the fuel tank within the range of the vernier scale. 8. Regularly take samples from the fuel tank for testing to check the contamination status of the oil.
2) Maintenance methods for hydraulic systems: a. Simple fault diagnosis method; b. Schematic analysis method; c. Analysis and troubleshooting methods for common faults of hydraulic valves. Hydraulic valves are components used to control the pressure, flow rate, and direction of hydraulic systems. The reasons for hydraulic valve failures usually include: improper component selection, poor component performance, poor machining accuracy and assembly quality of parts, insufficient spring stiffness to meet requirements, and poor quality of sealing components; In addition, there are factors such as dirty oil and high oil temperature.
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