Cause Analysis And Countermeasure Of Vibration Fault Of Feed Water Pump Motor

- Nov 20, 2018-

Cause Analysis and Countermeasure of Vibration Fault of Feed Water Pump Motor

During the operation of the equipment, the bearing vibration of the 4ZDG-12 feed pump motor suddenly increased. If it is not processed in time, it will cause damage to the motor bearing and hold the shaft. The large fluctuation of the boiler load will seriously affect the stability of the system steam supply. The vibration amplitudes of the load-side bearing of the 4ZD-12 feed pump motor in the horizontal, vertical and axial directions are measured by VM-63 to be 90, 75, 65μm, respectively. The vibration amplitude of the motor exceeds the vibration standard of less than 50μm.


Cause analysis and countermeasures

The axial vibration of the 4ZDG-12 feed pump coupling side bearing is good (vibration amplitude 25μm), and the motor and the water pump coupling are normal, indicating that the vibration is mainly caused by the motor side fault. The vibration of the motor base fastening bolt is large in the vertical direction, and the vibration swings regularly along the diagonal line. It is considered that the motor base has directional vibration phenomenon.

When the pump was stopped, it was found that the fastening plate on the lower part of the foot bolt with a vibration amplitude of 38 μm showed a crack of 3 cm, and the tightening force of the anchor bolt of the vibration amplitude of 35 μm was insufficient. The bolts are loose, causing the foot vibration to oscillate diagonally. After the welding and fastening treatment, the amplitude of the vibration of the vertical bolt of the foot bolt is measured to fall to the normal range; the amplitude of the vibration of the load bearing side of the 4ZDG-12 feed pump motor in the horizontal, vertical and axial directions is 52, 48, 41 μm, respectively. Compared with before the treatment, although the vibration amplitude is greatly reduced, the horizontal vibration still exceeds the enterprise standard of 50 μm. On February 10, the HG-8904C data acquisition fault vibration system was used to measure the vibration of the 4ZDG-12 feed pump motor load side bearing. The horizontal and vertical vibration signal spectrum is shown in Figure 2.

The vibration energy of the motor bearing is mainly concentrated in 1 frequency (50Hz), 4 times frequency (197.5Hz) and 2 times frequency (100Hz), and high frequency multiplication such as 3 times frequency (147.5Hz) and 8 times frequency (397.5Hz). According to the rotor imbalance fault, the mechanism and diagnosis of the 1st-frequency vibration amplitude and the loose connection of the rotor support system are presumed. The 4ZDG-12 feed pump motor generates fundamental frequency vibration due to rotor imbalance, and there is also a loosening fault.

In order to determine whether the 4ZDG-12 feed pump motor is mainly unbalanced fault, the fundamental frequency vibration phase measurement of the motor load side bearing is further measured, and the fundamental frequency vibration speed of the motor horizontal direction is measured to be 7.2 mm/s, phase 113°, vertical The fundamental frequency of the direction is 6.5 mm/s, the phase is 142°, and the phase is unstable. The phase difference between the two is 29°. Although the fundamental frequency vibration energy of the motor bearing is dominant, the vibration phase difference between the motor bearing in the horizontal and vertical directions is 29°, and the phase is unstable. Therefore, the vibration failure should not be dominated by the rotor imbalance. Because the unbalanced centrifugal force will generally produce a phase difference close to 90° in the horizontal and vertical directions of the bearing, and the phase is stable; at the same time, the motor bearing appears 2, 3, 4, 8 and other frequency doubling components, and 4, 2 octave vibration The energy is obvious and the vibration is unstable. It is considered that the main fault of the 4ZDG-12 feed pump motor is that the bearing fit clearance is too large.

Inspection of the motor bearing found that the front and rear end caps were easily removed, the high-temperature carbonized black material adhered to the outer ring surface of the free-side bearing of the motor, and the bearing chamber of the free-side bearing end cover of the motor was ground with obvious grooves, and the inner diameter of the bearing chamber was measured by the inner diameter micrometer to be 170.29 mm. The clearance between the outer ring of the bearing and the bearing chamber is 0.29mm, and the clearance tolerance is too large, and the tolerance of the normal bearing outer ring and the bearing chamber is (170±0.02) mm. This can easily cause the bearing temperature rise to rise sharply and burn out.

After the cleaning, brush plating and turning treatment of the motor shaft end cover bearing chamber, the interference of 0.01 mm is left, and after re-assembly, the horizontal, vertical and axial vibration amplitudes of the motor bearing are 17, 11 and 10 μm, respectively. The result met the requirements.

in conclusion

The vibration frequency of directional vibration, rotor imbalance, large rolling bearing clearance and other faults is mainly manifested in the speed of the frequency and its multiplier, and there is a great similarity. The phase difference of the directional vibration such as looseness of the base, basic resonance, and deformation of the body is generally close to 0° or 180° in two directions perpendicular to each other, and the phase is unstable; and the imbalance caused by the inherent imbalance of the rotor, the bending of the rotor, and the sudden imbalance are caused. The phase difference between the two directions perpendicular to each other is close to 90°, and the phase is relatively stable; the vibration frequency with large gap of the rolling bearing is the rotational frequency, and the high frequency doubling component is obvious. After the rotor imbalance is removed and the frame is loose, a large bearing clearance can be considered. Free paper reference network. Therefore, there are two or more composite vibration faults that need to be carefully analyzed and judged from various aspects such as vibration frequency, phase difference, vibration direction, and vibration location, in order to accurately find the location and cause of the fault, and propose solutions. Causes and countermeasures for vibration failure of feed pump motor.

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