The axial vibration of the steam turbine bearing seat was too large. After a comprehensive inspection, it was found that the bearing pad and sleeper support pad was worn, the anti-rotation pin was severely worn, and the pin hole was worn out. Due to the wear of the support pad, the elevation sank by about 0.75mm.
Treatment measures:
(1) Replace the upper tile sleeper insulation block and check the contact condition;
(2) Ultrasound examination of tile surface (no abnormality was found);
(3) The upper tightening hoop is used to grind the deformed pin hole, and use the sleeve treatment;
(4) Re-adjust the position of the bearing bush and the elevation of the bearing seat according to the size of the oil baffle pocket. The bearing is raised by 0.45 mm, the bearing seat is raised by 0.30 mm, and the torque of the anchor bolts is tightened according to the standard.
After treatment, the vertical and horizontal vibrations of the bearing seat are obviously improved, but the problem of large axial vibration still exists.
Again, after testing and analysis of bearing vibration, at full load:
(1) The bearing shaft vibrates about 80 μm;
(2) The horizontal and vertical vibration of the bearing seat is not large, less than 30 μm;
(3) The axial vibration of the bearing seat reaches 140 μm;
(4) The frequency spectrum of axial, vertical and horizontal vibration is dominated by the 50 Hz component, and the remaining frequency components are few.
Treatment measures:
(1) In the cranking state, the dial indicator of the frame tests the radial sway of the rotating shaft; tests the deviation of the opposite wheel;
(2) Disassemble the bearing, measure the journal lift, the journal sway, the bearing seat lift, the contact between the pad at the bottom of the bearing seat and the dimple, the bearing tightness, and the working state of the black gold surface;
(3) Check the tightness of the 4 anchor bolts of the bearing seat;
(4) Counterweight. The first counterweight plan: add 292 g at 140° of the tail disk of the exciter. The second counterweight plan: remove the counterweight of 300 g at 86° and 387 g at 170° at the tail disc of the exciter, and add 292 g at 332°.
After two counterweights, the vibration of the bearing is reduced, but the axial vibration of the bearing seat remains above 200μm. What is going on?
After analysis and discussion, it is known that there is a large axial vibration of the bearing seat, and its vibration frequency is consistent with the rotational speed. In terms of vibration properties, it is a common forced vibration. Similar to the radial general forced vibration diagnosis, the axial dynamic stiffness of the bearing housing should be detected first. Most of the causes of axial vibration are insufficient axial rigidity of the bearing seat, especially the looseness between the platen and the foundation; followed by the insufficient axial structural rigidity of the bearing seat and the generator end cover bearing. When the radial vibration of most turbo-generator units is not large, it is only necessary to eliminate the defect of insufficient connection rigidity of the bearing seat.
Judging from the site situation, the bearing seat has insufficient rigidity. The reasons may include:
(1) Insufficient tightening force of the bearing seat anchor bolts;
(2) The secondary grouting part of the bearing seat is loose and cracked. During the construction of the steam turbine, this problem may be caused due to the influence of seasons, temperature and other factors;
(3) The overall rigidity of the bearing seat decreases. Long-term over-standard tile vibration will cause fatigue damage to the bearing seat and affect the overall rigidity of the bearing seat. The long-term axial vibration of the bearing seat may also form a vicious circle, which reduces the overall rigidity of the bearing seat (such as defects such as bearing seat cracks).
Figure 3 shows the schematic diagram of the traditional unit bearing seat foot. It can be seen that it is a rectangular symmetrical arrangement with a large span, and the middle part of the bearing seat is bound to have the risk of insufficient rigidity. However, the feet of the bearing seat of the Alstom million unit are arranged symmetrically in a parallelogram, which shortens the span of the bearing seat and increases the width, and the rigidity of the middle part is bound to be better.
In the subsequent shutdown and maintenance, the reasons for the deterioration of rigidity should be mainly checked. The following aspects can be considered:
(1) Re-check the tightening force of the bearing seat anchor bolts;
(2) Careful inspection of the grouting part of the anchor bolts at the bottom of the bearing seat;
(3) The overall inspection of the bearing seat, especially whether there are cracks.