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Cause Analysis of Turbine Bearing Vibration 2020-03-31


【Abstract】 In the first phase of a power plant, two 660MW coal-fired steam turbine generator units are built. The steam turbine model is N660 / 24.2 / 566/566 (cylinder), which is produced by Shanghai Steam Turbine Co., Ltd. based on German Siemens technology. Three-cylinder, four-exhaust steam turbine. This article introduces the causes and solutions of abnormal vibration of the # 2 steam turbine # 1 bearing pad.

 

[Keywords] mass imbalance; double frequency vibration; rotor counterweight

 

1, equipment overview

 

The first phase of Huahua Power Plant installed two 660MW coal-fired steam turbines. The steam turbines are N660 / 24.2 / 566/566 supercritical, once reheated, single-shaft, three-cylinder, four-exhaust steam, condensate Steam Turbine, High-Medium Pressure Steam Turbine (HP-IP) is a hybrid type with impulse adjustment stage and reaction pressure stage. The steam turbine bearing adopts two supporting methods, and each segment of the rotor is supported by two bearings. There are 6 support bearings for the steam turbine and 2 support bearings for the generator. The turbine bearings use a leading edge tilting pad radial bearing with an oil groove (LEG). This type of bearing structure has good stability.

 

Unit # 2 was put into operation in August 2007.

 

2, the event

 

The # 1 bearing vibration after # 2 机 机 生产 production is slightly large. Until the spring of 2013, the # 1 bearing vibration value was X: 95 μm, Y: 105 μm. Before the shutdown, contact Henan Electric Power Test Research Institute to measure the vibration, based on the measured data. During the overhaul of the # 2 unit, weight the high and medium pressure rotors, and add 575 grams and 590 grams of counterweights at 20 ° in the opposite direction of the # 1 and # 2 watt zero positions (set to the zero position of the flying hammer). After the unit was turned on, the vibration situation did not improve. Before the # 2 machine's 2014 660MW load, the vibration values ??were X: 109 μm and Y: 102 μm. The magnitude of bearing vibration of a turbo-generator set is directly related to the safe operation of the unit. Abnormal vibration has become an important hidden danger for the stable operation of the unit.

 

3.Cause analysis

 

In order to analyze the bearing vibration of # 2 汽轮机 # 1, relevant experts such as the Local Electric Power Test Research Institute, Xi'an Thermal Engineering Research Institute, and the professional and technical personnel of this unit were invited to hold a special analysis meeting. Through analysis, it was agreed that: ① There is a first-order quality inferiority of the high and medium pressure rotors. balance. ② The # 1 bearing has a poor constraint on the rotor.

 

Before the unit was shut down, in order to determine the rotor mass imbalance, the local electric power test institute was invited to measure the vibration. The analysis of the vibration wave chart found that the vibration amplitude was in the doubling frequency region, which also verified that the rotor mass imbalance was causing # The main reason for the abnormal vibration of the # 1 bearing.

 

There are three reasons for the mass imbalance of the turbo-generator rotor: ① The original imbalance. ② The parts fly off and become loose during the rotation. ③ Thermal bending of the rotor. According to the analysis experience of other power plants, the original imbalance is the main reason. These different forms of unbalanced vibration characteristics are introduced separately.

 

一 (1) Imbalance of original quality

 

The original mass imbalance refers to the imbalance that already existed on the rotor before the rotor began to rotate. They are usually produced during manufacturing or are replaced by rotating parts during maintenance. In addition to the conventional characteristics of amplitude and phase, the most significant characteristic of this imbalance is its "stability". This stability refers to the stability of vibration characteristics at a certain speed. The amplitude and phase are not greatly affected by the unit parameters. In the data measured before # 2 machine expansion and minor repair, when the rated speed of the unit and the working conditions are not different, the amplitude fluctuates about 20%, and the phase of the double frequency vibration changes within the range of 10-20. For being stable. For the new unit, the original imbalance will show up at the first speed increase, and the characteristics of the speed increase and decrease vibration data before the rotor is subjected to any processing are very repeatable.

 

二 (two) flying parts loose and loose

 

Turbine generator sets may have blades when the rotating parts fly off, and loose parts may include guard rings, rotor coils, couplings, etc.

 

The double-frequency vibration generated during the fly-off is sudden. It is dominated by a certain tile vibration or shaft vibration within a few seconds, and its amplitude rapidly increases to a fixed value. Adjacent bearings will also increase vibration, but the magnitude of the change is not as great as the former. This failure usually occurs when the unit is under a certain load.

 

(3) Rotor thermal bending

 

The main characteristic of the mass imbalance caused by the thermal bending of the rotor is the change of the frequency doubling vibration with time. With the increase of the parameters of the random group and the continuation of the running time under high parameters, the amplitude of the double frequency gradually increases, and the phase gradually changes accordingly. After a certain time, this change slows down and eventually remains basically unchanged.

 

The thermal bending of the rotor generally comes from the thermal stress of the original material. This state of heat bending is inherent and repeatable, so it can be handled in a balanced manner. As long as the rotor is not permanently plastically deformed, such thermal bending can be recovered. After the root cause of thermal bending is eliminated, the phenomenon of large one-frequency vibration will also disappear by itself.

 

S # 2 During the operation of the unit, the DCS data shows that the eccentricity of the rotor is ≤0.02mm. According to the maintenance records of the unit, the rotor bending after overhaul is 0.02mm, which is less than the manufacturer's design standard ≤0.03mm. During the inspection of # 2 machine, no looseness was found in any rotating parts, and the sound of running vibration of each shaft was checked normally for each bearing, and there was no friction sound at the shaft seal. # 2 汽轮机 # 1 After the initial vibration of the shaft vibration, the vibration values ??are X: 81 μm and Y: 83 μm, which are slightly larger than other bearing vibrations. Before the high and medium pressure rotor weights are performed, # 2 机 # 1 The vibration data has good repeatability during high speed and normal operation.

 

Based on the above analysis, the original mass imbalance of the high and medium pressure rotors is the main reason for the # 2 steam turbine # 1 bearing vibration.

 

4.Solution

 

According to the vibration measurement data of the local Electric Power Test Research Institute before the shutdown of the unit, and in combination with the current counterweight of our company's # 2 steam turbine high and medium pressure rotors, experts and professors from Xi'an Thermal Power Research Institute are invited to analyze the data and work out a counterweight plan.

 

During the large-scale minor repair of # 2 machine, the # 2 steam turbine # 1 bearing was inspected. The tiltable tile has a good appearance, no wear of tungsten gold, and good contact with the tile pillow and horn. Adjust the gap of the roof of the roof by 0.71mm and the right by 0.71. mm, in line with the manufacturer's design standards of 0.71 to 0.81mm, and the pillow pillow tightening force is 0.17mm, which is the upper limit of the manufacturer's design. At the same time, check and adjust the gap data of the bearing roof of the steam turbine # 2 and the tightening force of the tile pillow. The macro inspection of the tiltable tile is normal, the contact of the horn is good, and the contact of the horn at the bottom of the tile pillow is slight. Withdraw the 0.07mm spacers on the left and right sides of the # 2 bearing lower horn, the gap on the top of the bearing: 0.81mm on the left and 0.82mm on the right. Meet the manufacturer's design standards 0.76 ~ 0.86mm requirements. In order to adjust the tightness of the tile pillow, remove the 0.10mm washer on the upper left side of the bearing, and re-test the tightness of the tile pillow: 0.19mm on the left and 0.17mm on the right, which is the upper limit of the designed tightening force for the manufacturer.

 

The counterweight of # 2 汽轮机 # 1, # 2watt according to the configuration plan, # 1 watt counterweight situation: 288g / 330.25 °, 288g / 341.5 °, 200g / 37 °. # 2 tile counterweight situation: 200g / 319 °, 288g / 330.25 °, 288g / 4 °, 288g / 308 °. After overhaul, # 2 machine has no abnormal vibration when starting, and when it is critical, # 1 bearing vibration X: 58 μm, Y: 59 μm, the unit runs normally after grid connection, # 1 bearing vibration X: 50 μm, Y: 54 μm, reaching excellent standards.

 

5, concluding remarks

 

Rotor mass imbalance is the most common vibration failure of turbo-generators, which accounts for about 80% of the total number of failures. With the continuous improvement of manufacturing process, assembly accuracy and power plant maintenance quality, the occurrence of such failures is gradually decreasing. Even so, the imbalance of mass is still the main fault of the on-site unit vibration. In cooperation with the Institute of Electric Science to conduct on-site vibration measurement, the data is used to formulate an effective counterweight solution. The counterweight during the unit maintenance is to solve the unit vibration. The point is.


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