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Bearing Vibration Problems and Treatment Methods of Turbine Generator

Update:30-09-2020
Summary:

During the use of a turbine generator bearing, the vibr […]

During the use of a turbine generator bearing, the vibration was found to be severely exceeded by inspection, and it must be stopped for treatment before it can be used. If it is not handled, it is likely to endanger the safe operation of the turbine generator set and cause unnecessary accidents. Do many people have a question here? Why does the engine vibration become larger?

In general, there are three reasons for the large vibration of steam turbine engine bearings:

1. Rubbing vibration of moving and static parts;

2. The oil film is unstable or damaged, and the oil film vibrates;

3. The shafting center is not in the same position, the shafting mass is unbalanced, and the shafting system vibrates dynamically.

The main factors that cause the first engine bearing vibration are as follows:

(1) During installation, the gap between the static and dynamic parts is too small, mainly including the gap between the bearing bush and the bearing, the oil barrier gap, the generator windshield gap, the flow gap between the turbine blades and the cylinder block, the gap between the generator impeller and the stator, and the steam seal cavity. gap;

(2) The cylinder is hindered by thermal expansion and tilts relative to the rotor.

The main factors that cause the second engine bearing vibration are generally as follows:

(1) The lubricating oil supply is too small;

(2) Unload oil from the oil hole in the oil sac at the bottom of the bearing bush;

(3) The lubricating oil temperature is too high or too low;

(4) The lubricating oil quality is unqualified.

The main factors that cause the third vibration are generally as follows:

(1) The coupling fails to pass the alignment, and the shafting center is inconsistent;

(2) The superheat of inlet steam parameters is too low or changes frequently, and the center of the steam turbine rotor changes;

(3) Insufficient drainage or insufficient warm-up time, and the rotor and cylinder expansion are not synchronized;

(4) The temperature of the steam seal is too high, the center of the cavity moves up, and the center of the shafting is destroyed;

(5) Vacuum and exhaust steam temperature is too high or too low;

(6) The bearing seat is loose;

(7) Bearing wear;

(8) The main shaft of the steam turbine generator set is bent;

(9) The coupling bolt counterweight is unqualified, and the rotor mass is unbalanced;

(10) Turbine blades drop;

(11) The generator rotor counterweight is loose or dropped;

(12) Unbalanced mass of steam turbine rotor;

(13) The generator rotor mass is unbalanced.

After testing, it was concluded that the problem of large bearing vibration of steam turbine generator:

(1) When installing, the gap between moving and static parts is too small

After the shutdown, all the gaps between the dynamic and static parts such as the gap between the bushes, the bearing bush and the bearing, the oil baffle gap, the generator windshield gap, and the steam seal gap have been checked and treated. The size is within the range required by the manufacturer and there is no trace of friction.

(2) The cylinder is hindered by thermal expansion and tilts relative to the rotor.

During the flushing process, check that the axial and radial expansion of the cylinder is unimpeded, and the opposite side expansion is synchronized.

(3) The lubricating oil supply is too small

During the flushing process, the temperature of each bearing shell and the oil return temperature meet the requirements. The highest temperature of the bearing shell is #4 watt support bearing shell temperature 61.06℃, and the highest temperature of oil return is #4 watt 57.44℃. Under the manufacturer's guidance, the # 4 The oil inlet orifice of the bush is expanded from the original design value of 8mm to 10mm. The second start-up inspection: #4 bush bearing maximum temperature is 56.33℃, maximum oil return temperature is 52.65℃, which has no effect on vibration.

(4) Unload oil from the oil hole in the oil sac at the bottom of the bearing bush

During installation, all the oil holes in the bottom oil sac of each tile have been welded, and the oil will not be unloaded.

(5) The lubricating oil temperature is too high or too low.

During the first flushing, the lubricating oil temperature is adjusted between 32C~47℃ for many times. When the mother pipe oil temperature is less than 43℃, the vibration of #4 drops slightly by 8μm, and the subsequent flushing, the mother pipe oil temperature is controlled. Between 37°C and 41°C.

(6) Unqualified lubricating oil quality

 

 

After the shutdown, the lubricating oil tank was cleaned and the tiles were turned over. Only slight wear marks on the #1 bearing were found and the oil quality was checked by the production unit, which met the requirements.

(7) The coupling fails to meet the requirements and the shafting center is inconsistent

Check the original construction records of the installation unit and meet the manufacturer's requirements. And check the tightness of the coupling bolts, and there is no looseness.

(8) The superheat of inlet steam parameters is too low or changes frequently, and the center of the steam turbine rotor changes

Throughout the flushing process, the inlet steam parameters remain unchanged.

(9) Insufficient drainage or insufficient warm-up time, and the rotor and cylinder expansion are not synchronized

Measure the temperature of the drain pipe wall on the spot, all> 110℃.

(10) The temperature of the steam seal is too high, the center of the depression moves up, and the center of the shaft system is destroyed

The steam temperature of the shaft seal is adjusted within the design value of 126℃~190℃, and the vibration of each tile remains unchanged.

(11) Vacuum and exhaust steam temperature is too high or too low

Adjust the exhaust steam temperature of the vacuum between the design value of -60~-89kPa and the design value of 56℃~78℃, and the vibration of each watt will not change.

(12) Loose bearing seat

There is little vibration in the distant tile, and it is measured and touched on the spot without obvious vibration.

(13) Bearing wear

In the inspection of the tile turning, the #1 tile had slight wear marks, but the other bearings were not worn. After the tile turning, the vibration was not significantly improved after the tile was turned on.

(14) The coupling bolt counterweight is unqualified, and the rotor mass is unbalanced

Check the bolt counterweight record of the installation unit and meet the manufacturer's requirements.

(15) Blade of steam turbine

The steam turbine vibrated little, and no abnormal sound was heard on the spot.

(16) The generator rotor counterweight is loose or dropped

After the rush to stop, open the end covers at both ends of the generator and check that the counterweight is not loose or falling off.

(17) Bending of steam turbine or generator shaft

The vibration characteristics caused by the thermal deformation of the rotor are closely related to the temperature of the rotor and the steam parameters. Most of them occur in the load stage after the unit is started in cold state and the speed is fixed. At this time, the temperature of the rotor gradually rises, and the internal stress release of the material causes the thermal deformation of the rotor. Increased vibration. However, this large vibration occurred in the unit impulse stage, so it can be eliminated.

(18) Imbalance of rotor mass of steam turbine and generator

Set up a vibration analyzer to determine that the vibrations of #3 and #4 bearings are concentrated at 1 frequency, that is, bearing vibration caused by mass imbalance. The generator balance weight is re-weighted and the machine is turned on again. The maximum vibration of each bearing does not exceed 70μm. It fully meets the requirements of manufacturers and specifications, and can meet the needs of safe and stable operation of the unit.

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