柴油发电机组出现转机振动故障的分析处理和预防
2022-03-25
There are usually four reasons for the vibration of diesel generator set during early operation: imbalance, resonance, misalignment and mechanical failure. So, how to prevent turnaround failures? Let's go down.
1. Rotor unbalance
It is the most common cause of vibration, such as poor manufacturing of rotor, accumulation of foreign matters on rotor blades, poor balance of motor rotor, etc. Another reason for large vibration caused by imbalance is poor stiffness or resonance of equipment base. Keys and keyways are another cause of unbalanced vibration.
Thermal bending of rotating shaft is another phenomenon that causes rotor imbalance. In general, the unbalanced vibration caused by thermal bending changes slightly with the change of load. However, if the equipment foundation resonates with its rotation, severe vibration is very likely to occur. Therefore, the key to prevention is that the material of the rotating shaft must meet the requirements; Second, the transfer base must be solid and reliable.
2. Resonance
The resonant frequency in the system depends on the number of degrees of freedom; The resonance frequency is determined by mass, stiffness and attenuation coefficient. The resonance frequency of the rotating machine support shall be far away from any excitation frequency. For new installations, consult the manufacturer for the required foundation stiffness to achieve this purpose. There are two options for existing devices with the same resonance frequency and speed - minimizing the excitation force or changing the resonance frequency. The latter can be achieved by increasing the stiffness and mass of the system. When dealing with resonance problems, it is best to change the resonance frequency. Resonance may also be caused by misalignment of rotor and stator system components or mechanical and electrical faults.
The resonance frequency of harmonic at rotating speed is also easy to cause fault. They may also be induced by misalignment or mechanical and electrical faults. However, compared with the problems at the same frequency, the problems caused by these resonances are not common.
3. Misalignment
It may cause radial and axial excitation forces at speed and twice the speed. However, it must not be concluded that there is no alignment problem because there is no one or two of the above phenomena. At the same time, the thermal expansion of the unit shall be considered, and a gap of 1.5-3mm shall be reserved between a pair of couplings.
4. Mechanical failure
Poor quality couplings, bearings, poor lubrication and weak supports are the reasons for the excitation forces of different frequencies and amplitudes.
(1) Poor quality couplings are mainly manifested in poor casting quality, deflection and burr of connecting screw holes, and rubber washers are quickly damaged, which changes the coupling from soft connection to hard connection, resulting in vibration and wear.
(2) The replacement of radial bearing is generally simple. In order to avoid vibration, when replacing a new bearing, check the contact color of the outer ring of the bearing, and deal with the bearing seat if necessary.
(3) Axial fluctuation is the cause of another vibration problem of rotating machine, including coupling and bearing. Generally, the axial thrust of the rotating machine is constrained by the thrust bearing. However, severe axial vibration may occur if the axial alignment is poor and the rotor rubs axially.
(4) The bearing is weak, that is, the four feet are not on the same plane. When the rotating machine is fastened with bolts at these four points, if the bearings are misaligned, it will inevitably cause severe vibration. Therefore, when installing the rotating machine, several fastening points should be tightened symmetrically with appropriate torque. Loosen the dial gauge one at a time and measure the deformation vertically. If the vertical deformation is greater than. 05mm, a gasket shall be added at the foot of this support, and its thickness is equal to the deformation. Repeat the above process until the vertical deformation of each point is less than 0.05mm when loosening.
(5) The problems of rotating machine base and foundation may be the direct cause of excessive vibration. Therefore, the anchor bolts must have sufficient strength and the concrete foundation must be solid without holes. During the transfer operation, the anchor bolts should be frequently checked for looseness and fracture and eliminated in time. At the same time, check whether the support of the auxiliary connecting equipment of the rotating machine is firm.
In addition, the vibration of water pump caused by cavitation is also a common phenomenon. In addition, the radial rubbing between the rotor and the stator is also easy to cause vibration, which is the vibration induced by the excitation frequency. Therefore, pay attention to the dynamic and static clearance during the assembly of the rotating machine. In addition, the large axial flow fan has surge, and the steam turbine has bearing oil film oscillation. In short, after being familiar with the common causes of rotating machine vibration faults, you can also use various vibration meters to deal with and prevent vibration.
1. Rotor unbalance
It is the most common cause of vibration, such as poor manufacturing of rotor, accumulation of foreign matters on rotor blades, poor balance of motor rotor, etc. Another reason for large vibration caused by imbalance is poor stiffness or resonance of equipment base. Keys and keyways are another cause of unbalanced vibration.
Thermal bending of rotating shaft is another phenomenon that causes rotor imbalance. In general, the unbalanced vibration caused by thermal bending changes slightly with the change of load. However, if the equipment foundation resonates with its rotation, severe vibration is very likely to occur. Therefore, the key to prevention is that the material of the rotating shaft must meet the requirements; Second, the transfer base must be solid and reliable.
2. Resonance
The resonant frequency in the system depends on the number of degrees of freedom; The resonance frequency is determined by mass, stiffness and attenuation coefficient. The resonance frequency of the rotating machine support shall be far away from any excitation frequency. For new installations, consult the manufacturer for the required foundation stiffness to achieve this purpose. There are two options for existing devices with the same resonance frequency and speed - minimizing the excitation force or changing the resonance frequency. The latter can be achieved by increasing the stiffness and mass of the system. When dealing with resonance problems, it is best to change the resonance frequency. Resonance may also be caused by misalignment of rotor and stator system components or mechanical and electrical faults.
The resonance frequency of harmonic at rotating speed is also easy to cause fault. They may also be induced by misalignment or mechanical and electrical faults. However, compared with the problems at the same frequency, the problems caused by these resonances are not common.
3. Misalignment
It may cause radial and axial excitation forces at speed and twice the speed. However, it must not be concluded that there is no alignment problem because there is no one or two of the above phenomena. At the same time, the thermal expansion of the unit shall be considered, and a gap of 1.5-3mm shall be reserved between a pair of couplings.
4. Mechanical failure
Poor quality couplings, bearings, poor lubrication and weak supports are the reasons for the excitation forces of different frequencies and amplitudes.
(1) Poor quality couplings are mainly manifested in poor casting quality, deflection and burr of connecting screw holes, and rubber washers are quickly damaged, which changes the coupling from soft connection to hard connection, resulting in vibration and wear.
(2) The replacement of radial bearing is generally simple. In order to avoid vibration, when replacing a new bearing, check the contact color of the outer ring of the bearing, and deal with the bearing seat if necessary.
(3) Axial fluctuation is the cause of another vibration problem of rotating machine, including coupling and bearing. Generally, the axial thrust of the rotating machine is constrained by the thrust bearing. However, severe axial vibration may occur if the axial alignment is poor and the rotor rubs axially.
(4) The bearing is weak, that is, the four feet are not on the same plane. When the rotating machine is fastened with bolts at these four points, if the bearings are misaligned, it will inevitably cause severe vibration. Therefore, when installing the rotating machine, several fastening points should be tightened symmetrically with appropriate torque. Loosen the dial gauge one at a time and measure the deformation vertically. If the vertical deformation is greater than. 05mm, a gasket shall be added at the foot of this support, and its thickness is equal to the deformation. Repeat the above process until the vertical deformation of each point is less than 0.05mm when loosening.
(5) The problems of rotating machine base and foundation may be the direct cause of excessive vibration. Therefore, the anchor bolts must have sufficient strength and the concrete foundation must be solid without holes. During the transfer operation, the anchor bolts should be frequently checked for looseness and fracture and eliminated in time. At the same time, check whether the support of the auxiliary connecting equipment of the rotating machine is firm.
In addition, the vibration of water pump caused by cavitation is also a common phenomenon. In addition, the radial rubbing between the rotor and the stator is also easy to cause vibration, which is the vibration induced by the excitation frequency. Therefore, pay attention to the dynamic and static clearance during the assembly of the rotating machine. In addition, the large axial flow fan has surge, and the steam turbine has bearing oil film oscillation. In short, after being familiar with the common causes of rotating machine vibration faults, you can also use various vibration meters to deal with and prevent vibration.