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Vibration failure and maintenance of large long shaft deep well pump


A pumping station is formed by two deep Wells with an inner diameter of 18m and a depth of 31m and the upper workshop.  Jinshajiang water is fed into the deep well through 4 Dg1200 pipelines. At the upper part of the deep well, 20 sets of 30JD-19x3 sand control deep well pumps are installed on the reinforced concrete frame beam with a cross-section of 1450mm×410mm.  After a long time of installation and protection maintenance, the causes of vibration were investigated.  

A deep well pump related skills performance parameters model: 30JD-19X3, three-stage impeller flow: 1450m3/h drive shaft length: 24.94m, a total of 9 shaft pump diameter: 080mm pump shaft material: 40Cr speed: 985R /min thrust pad oil temperature: < 50℃ cooling water pressure: 0.8mpa Yang pipe diameter:  500mm head: 80m rubber bearing smooth medium: water without motor, single weight: 14T Vertical motor model JKL15-6 Additional power: 500kW additional voltage: 6000V additional current: 60A Motor rotor moment of inertia: 58kg•m2 motor weight: 4t motor and pump vertical and degree direction permissible amplitude value:  This deep well pump requires that the sand content of the water is not greater than 0.1%, the particle size is not greater than 0.2mm, and the first stage impeller of the pump should be immersed under the moving water level of 1m.  At present, during the flood period in July and August, deep well pumping jinsha River water has a maximum sediment concentration of close to 20%.  

Two, vibration fault judgment pump and motor in the operation of vibration, when conditions, first should disconnect the coupling between the two, analyze the vibration source is from the pump or the motor, and carefully review the vertical motor base and the pump connection fixed bolt can tighten, the degree of the device can be out of error.  

1. Motor vibration source and judgment  

(1) Whether the rotor task speed is close to the critical speed.  By calculating the changing stiffness of the motor shaft and the torsional vibration frequency of the motor can be close to the attack resonance with the critical speed of the motor, the pump angular frequency and the power grid frequency.  In particular, when the motor is used for the first time, the vibration failure should be analyzed and calculated.  The task speed of the motor rotor should be at least 25% below the critical speed or about 40% above the critical speed.  In the analysis of the motor rotor mass can not be simplified into a centralized mass condition, but along the shaft spread, so the analysis of critical speed should be analyzed to the second and third order critical speed.  

(2) Unbalance of motor rotor.  Motor rotor unbalance is the most important and rare cause of vibration, such as:  For 17 # and 19 # motors, the vibration velocity of the motor is 9.8-10mm/s measured by the speed vibration meter (displacement meter). Compared with the IS02372 vibration velocity specification, the vibration velocity of class III machinery should be less than 4.5mm/s, and in the condition of 9.8-10mm/s, the amplitude of the motor measured by the vibration meter reaches 0.30mm.  In order to find out the degree of unbalance of the motor rotor, we made two pairs of steel frame set up two parallel rails at the scene (should pay attention to the steel frame should be sufficient stiffness), the surface of the rail is treated into a smooth cleaning face, with the degree of instrument with the rail surface adjustment degree and fixed.  Review of the motor rotor on two rails, with the hand to promote the rotor outlet metering pump rolling repeatedly, each time to wait for its static, on the rotor above the mark.  Paste the sticky material on the symmetric point of the important position, and then rotate the rotor repeatedly until the rotor can stop in any position, confirm that the motor rotor has reached the static equilibrium state.  The equivalent mass is used instead of paste to realize the task of balancing the rotor of the motor.  If the above method is still not able to deal with the problem, it is necessary to make the motor rotor dynamic balance test.  After adding 45-5G balanced component to one side of the rotor, the amplitude of the above two motors is reduced to 0.05mm, and the vibration velocity measured by the displacement meter is about 2.1mm/s.  

(3) For the motor that has been normally used for a period of time, the vibration cause should be reviewed whether the bearing clearance is too large, whether the fixing screw of the shaft seat is loose, whether the shaft is worn and tortuous or a certain part of the winding is short circuit, the air gap is uneven, and the annular clearance between the rotor and the stator is not more than 10%.  In particular, it is worth noting that when the motor amplitude value is close to the standard value, that is, it is still in the condition of passing the scale, the motor amplitude value will often exceed the limit after the load, because all the factors of deep well pump transmission system vibration are the consequences of mutual influence and unique action.  


2. Pump body vibration source and judgment  

(1) Vibration caused by pump installation and disassembly deviation.  The vibration of pump body will be caused by the out-of-deviation of the degree of pump body and thrust pad after installation and the verticality of water pipe, and the three master values are positively related.  After the pump body is installed, the total length of the lifting water pipe and the pump head (excluding the filter screen) is 26m, and both are suspended. If the vertical deviation of the lifting water pipe is too large, the violent vibration of the lifting water pipe and the shaft will be formed in the rotation of the pump.  When the vertical deviation of the lifting pipe is too large, the alternating stress will occur during the operation of the pump and cause the breaking of the lifting pipe.  After the deep well pump is removed, the vertical error of the water pipe should be mastered in 2mm within the total length scale.  The horizontal and horizontal error of the pump is less than 0.05/1000mm.  For the pump head impeller static balance tolerance is not greater than 10g, after the assembly should be 8-12mm high and low series dynamic clearance.  The gap error between installation and disassembly is an important cause of pump vibration.  

(2) the vortex of the transmission shaft.  Vortex, also known as "rotation", is a kind of self-excited vibration caused by rotation axis. It has neither the characteristics of free vibration nor the type of forced vibration.  Its characteristic is that the shaft is reflected as rotating static between bearings. This vibration is not occurred when the shaft reaches the critical speed, but occurs in a larger scale and has less relationship with the rotational speed of the shaft itself.  The rotation of deep well pump is mainly caused by the insufficient smooth bearing. If the gap between the shaft and the bearing is large, the rotation static direction is opposite to the rotation direction of the shaft, which is also called the vibration of the shaft.  Special is the deep well pump shaft is very long, rubber bearing and shaft fit clearance of 0.20-0.30 mm, exists certain gaps when the shaft and bearing, shaft and bearing different heart, central distance is larger, and lacking a smooth clearance, such as deep well pump rubber bearing the smooth water supply pipe rupture, infarction, wrong operation to form water supply is adequate or not timely conditions, such as are more likely to emerge.  When a brake rotating shaft neck at one point contact with the rubber bearings, shaft neck was bearing to its tangential force, a force direction contrary to the direction of the axis of rotation speed, the power to the axis of translation, the mechanical effects of proportion in a counterclockwise torque and a role in the middle of the shaft neck force, this force is parallel to the bearing wall on the tangent of the point of contact,  And there is a tendency to make the journal down, so the journal will be pure rolling along the bearing wall, commensurate with a pair of internal gears, so as to form a static rotation opposite the axis rotation direction.  This has been proved by the situation in our daily operation. This situation will cause rubber bearings to burn for a little longer.  

(3) Vibration caused by overload.  The thrust pad of the pump body is made of tin-base babbitt alloy, and its licensed load is 18MPa (180kGF /cm2).  When the pump body is started, the smooth thrust pad is in the smooth boundary condition.  The pump body is equipped with electric butterfly valve and manual gate valve at the water outlet.  When the pump starts up, close the electric butterfly valve at the same time. Because the valve plate cannot be opened due to sediment deposition or the manual gate valve is closed due to human factors, and the exhaust is not timely, the violent vibration of the pump body will be formed and the thrust pad will be burned quickly, such as 15 # and 17 # pumps.  

(4) Outlet turbulent vibration.  In the pump discharge progressive set Dg500 short tube, check valve, electric butterfly valve, manual valve, head and water hammer cleaners, turbulence of water static scene in the pulse of the onset of manners, together with the valve block, part of the resistance is bigger, cause a change in the momentum and pressure change, and acting on the pipe wall on the pump body make its vibration, it can inspect pressure gauge the pulsation of the numerical picture to explain.  The fluctuating pressure and velocity field in the turbulent flow have been transferred to the pump energy. When the main frequency of the turbulent flow is close to the natural frequency of the deep well pump system, the system will drain energy and cause vibration.  To increase this vibration effect, the valve should be completely opened, the short pipe should be the corresponding length and add support.  After this treatment, the vibration value is significantly reduced.  

(5) Torsional vibration of deep well pump.  The long shaft deep well pump and motor are connected by elastic coupling, and the total length of the drive shaft is 24.94m.  In the operation of the pump, there is the superposition of the main vibration of different angular frequencies.  The result of decomposition of two simple harmonic vibration with different angular frequencies is not sure to be simple harmonic vibration, that is, there are two changes of freedom vibration outside the pump body, which is unavoidable.  This vibration significantly affects and damages the thrust pad.  Therefore, in order to ensure that each three-dimensional thrust pad has a corresponding oil wedge, we will replace the original equipment with the regular 68# oil in the random explanation book to 100 # oil, improve the viscosity of the smooth oil of the thrust pad, so that the formation and maintenance of the dynamic pressure smooth slide of the thrust pad oil will not be damaged.  

(6) vibration caused by mutual influence of pumps installed on the same beam.  Deep well pump and motor are installed on two reinforced concrete frame beams with a section of 1450mmx410mm, and the concentrated mass of each pump and motor is up to 18T. The vibration of two adjacent pumps on the same frame beam is another vibration system with two degrees of freedom. When the vibration of one of the motors exceeds the standard and is tested without load,  That is, the elastic coupling is not connected and idling motor, another normal operation of the pump motor amplitude value to about 0.15mm, this situation is not easy to be detected, should be paid attention to.  


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