The wind turbine is on fire. Is there too much grease inside the front bearing of the motor?
December 26, 2021
A wind farm "generator overspeed" shut down, and then triggered multiple faults such as "generator bearing 1 temperature is too high". After accident investigation, the root cause was improper grease filling and too much grease in the front bearing of the generator. Check it out below:
Analysis of the cause of the accident: filling amount of lubricating grease The filling amount of grease is suitable to fill one-third and one-half of the space between the bearing and the bearing housing. If too much grease is added, the heat dissipation of the bearing rolling elements will be blocked, and the grease will deteriorate or soften. Bearings used for high-speed rotation should only be filled to one-third or less. For bearings that rotate at low speeds, in order to prevent foreign matter from entering the bearing, the shell space can be filled. Figure 17 shows the location of the front bearing oil box and manual oil filling port of the generator, while the automatic oil filling port is directly above the front end cover of the generator bearing. According to the oil filling and oil draining method of the generator bearing of the accident unit, as long as the lubricating pump of the generator automatically fills the oil normally, the grease is filled between the front and rear end covers of the bearing and the entire bearing housing. Therefore, the amount of oil injected into the bearing of this type of generator, the amount of grease inside the bearing will far exceed the normal filling amount. The generator bearing of the accident unit uses high-temperature grease. According to the dripping point temperature provided by the grease manufacturer, it is about 250 ℃. When the dripping point is reached, the Base Oil will be separated and lost from the grease, and the ignition point of the lost base oil is about Generally, when the bearing is locked, the temperature of the front end of the generator shaft should be above 600°C, far exceeding its ignition temperature. As far as this accident is concerned, when the bearing cage is damaged, the friction between the inner and outer rings of the generator bearing and between the inner ring of the bearing and the generator shaft will cause violent heat generation. The bearing and the front end of the generator shaft will heat up seriously. Evaporation occurs when heated. When the evaporated grease is sprayed from the front end of the generator bearing, it will burn if the temperature exceeds the ignition point of the grease. The rolling elements of the bearing and the raceways of the inner and outer rings of the bearing are seriously blackened, and there is a melting phenomenon between the inner ring of the bearing and the generator shaft (the material is steel, the melting point of pure iron is 1535 ℃, and the melting point of steel is about 1515 ℃. As the content of carbon or other components in the iron increases, the melting temperature will decrease. For example, the temperature of the bearing inner ring and the front end of the generator shaft will be It is very high, which can cause a large amount of base oil to quickly vaporize. After a large amount of combustible gas is sprayed from the front bearing end cover of the generator, it is ignited at the front end of the generator shaft or at the torque limiter, causing ignition and combustion.
Accident prevention measures When the generator set has been used for a certain number of years, it is inevitable that the generator bearing will be damaged and stuck. The previous analysis shows that if there is no large amount of grease inside the front bearing of the generator, it will not cause the spread of fire and cause a fire.
Therefore, in order to avoid the recurrence of such accidents, effective measures should be taken to strictly control the amount of grease inside the bearing to prevent a large amount of grease from depositing in the generator bearing. More accurate control of the amount of oil injected into the front bearing of the generator is the fundamental method to avoid fire accidents.
As far as this accident is concerned, it is recommended to adopt manual oil filling method, cancel automatic oil filling, accurately control the oil filling amount and grease position manually, and clean up the waste oil inside the bearing on time; for newly produced generators, it is recommended to use the oil filling position and oil discharge method. Make improvements to avoid excessive waste oil deposits inside the bearing.
