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Treatment Of Abnormal Bearing Temperature

Source:  skf bearing  Time:  2021-07-20

1. Background introduction


The gas turbine power plant adopts the STAG-109FA-SS single-shaft combined cycle unit, which is composed of a PG9351FA gas turbine, a two-cylinder dual-flow steam turbine with a D10 three-pressure reheat system, a 390H hydrogen-cooled generator, and a triple-pressure reheat but with a condenser The natural circulation waste heat boiler for deoxygenation is composed of [1]. Except that the waste heat boiler is supplied by Hangzhou Boiler, the rest are provided by Harbin Power Equipment Co., Ltd. and General Electric Company of the United States. The gas turbine, steam turbine and generator are rigidly connected in series on a long shaft, and the shaft configuration is in the form of GT (gas turbine)-ST (steam turbine)-GEN (generator).


2. Status of bearing operation


The gas turbine unit has been shut down for a long time after being overhauled. After the cold start-up, it was found that the temperature of the bearing bush metal of the unit 4# was high. When the unit is running at full load, real-time monitoring of 4# bearing bush, 5# bearing bush and lubricating oil inlet temperature is carried out. Through the monitoring data, it can be found that when the unit is operating at full load, the temperature measurement points of the two bushes of 4# bearing are near the high alarm value of the bearing bush temperature, while the temperature of the 5# bearing bush is basically below 100 ℃, and the bearing bush has temperature during operation. High abnormal phenomena threaten the safe and stable operation of the unit.

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3. Analysis of bearing temperature abnormality


The bearing is a tilting pad bearing, and the surface of the bearing pad is covered with a layer of babbitt alloy. When the temperature is high or the bearing pad is subjected to abnormal stress, the babbitt alloy will be deformed. When the bearing is working normally, an oil film will be established between the bearing bush and the high-speed rotor, and the oil film plays the role of lubrication and cooling. In operation, the successful establishment of the oil film is an important guarantee for the normal operation of the bearing. There are many factors that affect the establishment of the oil film, including the quality and temperature of the lubricating oil, the amount of lubricating oil, the gap between the bearing bush and the rotor, and the pressure holding capacity of the lubricating oil in the bearing. In addition, the 4# bearing is adjacent to the shaft seal of the high and medium pressure cylinder, which does not rule out the influence of the shaft seal on the temperature of the bearing bush when the shaft seal leaks a lot.


(1) Analyze the influence of lubricating oil quality and oil temperature on bearing temperature


The oil quality of the lubricating oil affects the establishment of the oil film, and situations such as unqualified lubricating oil particles often occur during operation. After investigation, it was found that the factory would regularly sample and analyze the lubricating oil. At the same time, the unit used an external oil filter to filter the lubricating oil for a long time, and no problems with the lubricating oil quality were found.


(2) Analyze the influence of lubricating oil temperature on bearing temperature


During the operation of the unit, the operating personnel monitor the lubricating oil temperature at all times to ensure that the lubricating oil temperature is within the normal allowable range. At the same time, by looking at the two-day operating data, it can be seen that the lubricating oil inlet temperature has been around 41°C, which is within the normal operating range.


(3) Analyze the impact of shaft seal leakage at the high and medium pressure cylinders on the bearing temperature


When the temperature of the 4# bearing bush was high, the maintenance personnel of the plant repeatedly inspected the surrounding environment of the 4# bearing and used a spot temperature gun to measure the temperature of the shaft seal on the medium pressure cylinder side. No abnormal phenomenon was found.


(4) Analyze the influence of lubricating oil intake on bearing temperature


The lubricating oil intake affects the quality of the oil film establishment. During the construction of the unit, the lubricating oil intake is specified by the Electric Power Design Institute and generally does not change. Checking the maintenance history of the unit, it was found that the unit had a high bearing bush temperature. After communicating with the manufacturer, the inner diameter of the bearing oil inlet hole was adjusted to increase the oil intake of the 5# bearing and reduce the oil intake of the 4# bearing. The amount of oil, trying to reduce the temperature of the 5# bearing bush, but the adjustment did not reach the expected effect. The follow-up investigation found that the bearing bush temperature measuring points of 4# and 5# of the factory were connected reversely.


(5) Analyze the impact of the bearing bush and rotor clearance on the high temperature of the bearing bush


The bearing of this unit has been adjusted centrally and the 5# bearing is raised by 0.17mm. However, the unit operation found that the bearing bush temperature change is not as obvious as expected. It is suspected that the uneven distribution of the rotor load will cause the bearing bush to deform, resulting in poor quality of the oil film in the bearing. , Unable to effectively cool the bearing bush, resulting in high temperature of the 4# bearing bush.


4. Bearing maintenance


After analysis, this bearing inspection includes two items. The first item is to restore the bearing orifice plate to the initial design value. The second item is to remove the 4# and 5# bearings and inspect them, and if necessary, the bearing Re-poured. After dismantling the bearing, first check the appearance of the bearing bush. It is found that there are obvious indentations in the central area of the lowermost bush of the bearing. This area is in contact with the hard steel area on the inner surface of the bearing and is the main stress area of the bush. This phenomenon can be It is inferred that the pad has received a relatively large load, and the bearing pad is likely to be deformed. In order to further verify the appeal inference, the lower half of the bearing was subjected to the step of pressing the false shaft, and the contact between the bearing bush and the rotor was checked. After pressing the false shaft, the red lead on the bearing bush was unevenly distributed. It can be judged that the bearing bush has been deformed and needs to be returned to the factory for re-pouring. After the bearing bush is poured, the bearing is reinstalled into the unit, and the bearing and rotor Find the center and restore the relative position of the bearing and the rotor to the state before repair.