Hazard of reverse flow failure of hydraulic oil

Since the driving medium in the wind turbine brake system (spindle brake and yaw brake) uses low-viscosity hydraulic oil, and the actuator (piston) of the brake system constantly moves during operation, the inevitable presence of grease Leakage problem. On the one hand, grease leakage will cause the pressure of the hydraulic system to drop, which cannot meet the technical requirements of the wind turbine; on the other hand, the leaked grease will cause pollution inside the unit and bring safety hazards to the operation of the operation and maintenance personnel. In order to solve the problem of hydraulic oil leakage caused by piston movement, brake and hydraulic system manufacturers usually set the hydraulic oil drain circuit in the hydraulic circuit inside the brake and hydraulic system to guide the leaked hydraulic oil to the hydraulic system fuel tank. In this way, the pressure drop caused by the leakage of the hydraulic oil can be avoided, and the leaked hydraulic oil can be recycled and reused, which has an environmentally-friendly and efficient effect. The drainage system connection structure of the hydraulic system is shown in Figure
1.The structure of the drain circuit of the brake is designed according to the sealing structure inside the brake. The internal sealing structure of the brake generally comprises two rubber sealing rings surrounding the piston, which are divided into a sealing ring and a dustproof ring according to the function. The sealing ring is located on the side close to the bottom of the cylinder (ie, the side away from the friction plate), and the pressure can be withstand high, reaching tens of MPa, ensuring that the hydraulic oil does not leak under the pressure of the brake; the dust ring is located Keep away from the side of the bottom of the cylinder, the pressure can withstand relatively small, usually 5bar -10bar Within the scope, the main function is to prevent various impurities on the outside of the brake from penetrating into the brake and contaminating the hydraulic oil. During the up and down movement of the brake piston, hydraulic oil leaks from the bottom of the cylinder to the seal ring and the dust seal. Then the leaked hydraulic oil enters the brake drain circuit and is then led back to the tank to return to the hydraulic system. Pressure loop. Generally, the fuel tank position of the wind turbine hydraulic system is higher than the yaw brake 2 Meter - 3 meters, that is, the leaking hydraulic oil must accumulate to the oil return pipe filled in the drain circuit before entering the fuel tank, so the dust ring needs to withstand the pressure caused by the hydraulic oil in the return pipe. The drain circuit of the yaw brake.

However, the actual operation and maintenance work found that the hydraulic oil that should have been led back to the tank was accidentally spilled from the yaw brake piston. After the hydraulic oil overflows from the upper piston of the yaw brake, it drops on the brake disc, causing pollution to the friction environment of the yaw friction pair (friction disc and brake disc), resulting in the friction coefficient of the yaw friction pair is no longer uniform. The friction performance is no longer stable, and there is a large vibration and noise. The friction material of the friction plate is susceptible to oil intrusion and denaturation due to the resin-based composite material, and the wear rate is greatly increased. The working life of the friction plate is rapidly decreased, exceeding the wind power. The inspection and maintenance period of the unit, if not found in time, will cause serious accidents in which the brake disc is worn by the friction plate back plate. The yaw brake friction plate is contaminated by grease as shown in Figure
3.Analysis of the Causes of Reverse Flow of Hydraulic Oil

According to the working principle of the hydraulic oil drain circuit introduced in the previous section, if the sealing ring of the yaw brake sealing structure fails, a large amount of hydraulic oil will be leaked, and the pressure of the hydraulic system will drop rapidly, and the actual situation encountered at the site is There was no significant grease leakage and there was no significant change in system pressure. Therefore, the direct cause of leakage of hydraulic oil is that the pressure between the dust seal and the seal exceeds the tolerance of the dust seal. The pressure between the wiper ring and the seal ring is caused by the hydraulic oil in the return line connecting the yaw brake and the fuel tank, and the pressure is calculated as Equation (1).

P=tgh(1)

Where ρ is the hydraulic oil density, 800 kg/m3;

g is the acceleration of gravity, 9.85m/s2;

h is the elevation difference between the fuel tank and the yaw brake, in 3m.

Calculated by formula (1), the pressure caused by hydraulic oil is 23640Pa, and the fuel tank should be connected to the atmosphere, there is no negative pressure inside, and the minimum pressure that the dust ring can withstand is 50000Pa, so theoretically, the yaw brake leaks. The hydraulic fluid should be returned to the tank.

After investigation and research, the possible reasons for the leakage of the drainage circuit include the following three aspects:

(1) The dust ring is invalid;

(2) There is a negative pressure inside the fuel tank;

(3) The drain passage on the hydraulic valve block is connected to the pressure relief oil passage.

According to the test, the reason (1) is inconsistent with the actual situation, and the condition of the cause (2) is not established. Therefore, the reason for the preliminary determination of the leakage of the drain circuit is that the drain line in the valve block is connected with the pressure relief oil line or other oil circuit with pressure, so that extra pressure occurs at the end of the drain line, causing leakage of hydraulic oil in the drain circuit. .

Optimized solution for faults

For the design problem of the drainage circuit of the wind turbine hydraulic system, there are two common solutions at present: the return pipe scheme and the oil collection tank scheme. The oil drain circuit shown in Figure 1 is the return pipe scheme. The use defects of this scheme have been described in detail in the first section and will not be described here.

The oil collecting bottle solution means that the oil collecting bottle is directly connected to the drain port of the yaw brake, and the oil collecting bottle is used for collecting the hydraulic oil overflowing from the yaw brake seal ring, and the bottom of the oil collecting bottle has a breath communicating with the outside air. The mouth ensures that the hydraulic oil can flow smoothly into the collection bottle. The scheme is also widely used in wind turbines. Its advantages are simple structure, convenient maintenance, and effective avoidance of reverse flow of hydraulic oil. However, in the actual work process, the program has the serious consequences of not being able to accommodate a large amount of hydraulic oil leakage, resulting in serious pollution inside the wind turbine.

In order to solve the problem of the reverse flow of the hydraulic oil in the return pipe scheme and solve the defect of the leakage oil capacity of the oil collection bottle scheme, it is necessary to optimize and improve the two schemes, and the existing advantages of the two schemes need to be retained. After repeated trials and studies, the existing two schemes have been organically combined, and an optimized scheme for decontamination has been initially formed. The optimization solution is to retain the return line in the return line scheme, connecting a special oil collection bottle to the yaw brake that communicates with the hydraulic station drain line. The end cap of the special oil collection bottle is in addition to the common interface. In addition, add a return pipe through the oil return pipe and the spindle brake, and then connect to the hydraulic station drain port interface, as shown in Figure
4.The scheme not only preserves the energy-saving and environmental protection advantages of the return-oil pipe scheme, but also recycles the leakage hydraulic oil, and eliminates the disadvantages of insufficient hydraulic oil capacity of the traditional oil collection bottle scheme. In this scheme, the special oil collection bottle has a breathing port that communicates with the outside world to ensure that the pressure inside the bottle is equal to the atmospheric pressure, thereby solving the problem of hydraulic oil leakage caused by the pressure of the yaw brake drain port being higher than the upper limit of the dust ring pressure.