Through the analysis of vibration faults of large deep well pumps and various possible causes of vibration, a method for simple on-site judgment of motors and pumps is proposed.
Panzhihua Iron and Steel Co., Ltd. has built a large-scale deep well pumping station in the upper reaches of the Jinsha River. The pumping station consists of two deep wells with an inner diameter of 8m and a depth of 3m and an upper factory building. Jinsha River water enters the deep well through four Dg200 pipes. In the upper part of the deep well, 20 30JD-9×3 sand control deep well pumps are installed on reinforced concrete frame beams with a cross-section of 450mm×40mm. During the long-term installation and maintenance process, we made some explorations into the causes of vibration.
1. Relevant technical performance parameters of deep well pumps
Model: 30JD-9×3, three-stage impeller
Flow rate: 450m3/h
Transmission shaft length: 24.94m, 9 shafts in total
Pump shaft diameter: 080mm
Pump shaft material: 40Cr
Thrust tile oil temperature: <50℃
Cooling water pressure: 0.8MPa
Inner diameter of water pipe: 500mm
Rubber bearing lubrication medium: clean water
Machine weight without motor: 4t
Vertical motor model JKL5-6
Rated power: 500kW
Rated voltage: 6000V
Rated current: 60A
Motor rotor moment of inertia: 58kg·m2
Motor weight: 4t
The allowable amplitude value of the motor and pump body in the vertical and horizontal directions: <0.l0mm
This deep well pump requires that the sand content of the water quality should not be greater than 0.%, the particle size should not be greater than 0.2mm, and the first-stage impeller of the water pump should be immersed below the moving water level lm. At present, during the floods in July and August, the maximum sediment content of Jinsha River water pumped by deep well pumps is close to 20%.
2. Judgment of vibration faults
If vibration occurs during the operation of the pump and motor, if possible, the coupling between the two should be disconnected first, analyze whether the source of vibration comes from the pump or the motor, and carefully check whether the fixing bolts connecting the vertical motor base and the pump are Tighten and check whether the levelness after installation is out of tolerance.
． Motor vibration sources and identification
() Whether the rotor operating speed is close to the critical speed. It can be calculated by calculating whether the torsional stiffness of the motor shaft and the torsional vibration frequency of the motor are close to the critical speed of the motor, the pump angular frequency and the grid frequency to cause resonance. Especially when a motor is used for the first time and a vibration failure occurs, analysis and calculation must be carried out. The working speed of the motor rotor should be at least 25% lower than the critical speed or about 40% higher than the critical speed. During the analysis, it should also be considered that the mass of the motor rotor cannot be simplified to a concentrated mass, but is distributed along the rotating axis. Therefore, when analyzing the critical speed, the main critical speeds such as the second order and the third order should be analyzed.
(2) Unbalance of the motor rotor.
The unbalance of the motor rotor is the most important and common cause of vibration, such as: 7# and 9# motors. The vibration speed of the motor measured with a speed vibration meter (displacement meter) is 9.8-10mm/s. Compared with the IS02372 vibration speed standard, Class III machinery should be less than 4.5mm/s, and at 9.8-10mm/s, the amplitude of the motor measured with a vibration meter reaches 0.30mm. In order to find out the unbalanced degree of the motor rotor, we made two pairs of steel frames on site to erect two parallel rails respectively (it should be noted that the steel frame should have sufficient stiffness). The upper surface of the rails was treated to be smooth and clean. Use a level to adjust the rails. Level and secure the surface. During the inspection, place the motor rotor on two rails, push the rotor back and forth several times by hand, and mark the bottom of the rotor each time after it comes to a standstill. Paste a sticky substance on the symmetrical point of the biased position, and then rotate the rotor multiple times until the rotor can stop at any position, confirm that the motor rotor has reached a static equilibrium state. Replace the sticker with equivalent mass to complete the balancing work of the motor rotor. If the problem still cannot be solved by using the above method, the motor rotor needs to be dynamically balanced and inspected. After adding a 45-5g balance weight to the rotor side of the above two motors, the amplitude value was reduced to 0.05mm, and the vibration speed value measured with a displacement meter was around 2.mm/s.
(3) For motors that have been used normally for a period of time, the cause of vibration should be checked to see if the bearing clearance istoo large, whether the fixing screws of the rotating shaft seat are loose, whether the rotating shaft is worn and bent, or whether a certain part of the winding is short-circuited, the air gap is uneven, and whether the rotor and The annular gap unevenness between stators should generally not exceed 0%.
It is particularly worth noting that when the motor amplitude value is close to the standard value, that is, it is considered to be within the qualified range, the motor amplitude value will often exceed the standard after loading. This is because the vibration factors of the entire deep well pump transmission system interact with each other. and the result of joint action.
2.Pump body vibration source and judgment
() Vibration caused by deviations in pump installation and assembly. The levelness of the pump body and thrust tiles after installation and the verticality of the water pipe will cause vibration of the pump body. At the same time, these three control values are related to a certain extent. After the pump body is installed, the total length of the water pumping pipe and pump head (excluding the filter) is 26m, and they are all suspended. If the vertical deviation of the water pumping pipe is too large, severe vibration of the water pumping pipe and shaft will be caused during the rotation of the pump. . Excessive verticality deviation of the water pumping pipe will also produce alternating stress during the operation of the pump, causing the water pumping pipe to break. After the deep well pump is assembled, the verticality error of the water riser pipe within the total length should be controlled to ±2mm. The vertical and horizontal horizontal errors of the pump are <0.05/l000mm. The static balance tolerance of the pump head impeller is not greater than 0g, and there should be an up and down movement clearance of 8-2mm after assembly. Installation and assembly clearance errors are important causes of pump body vibration.
(2) Whirl motion of the drive shaft. Whirlpool, also known as “whirlwind”, is a self-excited vibration of the rotating shaft. It has neither the characteristics of free vibration nor the type of forced vibration. It is characterized by a rotary motion of the shaft between the bearings. This vibration does not occur when the shaft reaches the critical speed, but occurs in a larger range and has less to do with the speed of the shaft itself. The rotation of the deep well pump is mainly caused by insufficient bearing lubrication. If the gap between the shaft and the bearing is large, the direction of the rotational motion is opposite to the rotation direction of the shaft. This situation is also called shaft jitter. In particular, the transmission shaft of the deep well pump is very long, and the matching clearance between the rubber bearing and the shaft is 0.20-0.30mm. When there is a certain gap between the shaft and the bearing, the shaft and the bearing are not concentric, the center distance is large, and there is a lack of lubrication in the gap, such as in deep wells Shaking is more likely to occur when the lubrication water supply pipe of the pump rubber bearing is broken, blocked, or misoperation causes insufficient or untimely water supply. At a certain moment, the rotating journal is in contact with the rubber bearing at one point. The journal is subject to the tangential force given by the bearing. Assume that the direction of the force is opposite to the direction of the shaft’s rotational speed. This force is translated toward the axis center, and its mechanical effect is It is equivalent to a counterclockwise torque and a force acting on the center of the journal. This force is parallel to the tangential direction of the contact point of the bearing wall and has a tendency to move the journal downward. Therefore, the journal will move purely along the bearing wall. Rolling is equivalent to a pair of internal gears, which forms a rotary motion opposite to the direction of shaft rotation.
This has been confirmed by our daily operation. If this situation lasts for a long time, the rubber bearing will be burned.
(3) Vibration caused by overload. The thrust tile of the pump body is made of tin-based Babbitt alloy, and its allowable load is 8MPa (80kgf/cm2). When the pump body is started, the lubrication of the thrust shoe is in a boundary lubrication state. An electric butterfly valve and a manual gate valve are respectively installed at the water outlet of the pump body. When the electric butterfly valve is opened at the same time as the pump is started, the valve plate cannot be opened due to silt deposition, or the manual gate valve is closed due to human factors, or the exhaust is not released in time, etc., it will inevitably cause severe vibration of the pump body and quickly burn out the thrust tiles, such as 5 This is the case for # and 7# pumps.
(4) Turbulent vibration at the outlet. The Dg500 short pipe, check valve, electric butterfly valve, manual valve, main p
Link to this article：Analysis and treatment of common vibration faults of large long-axis deep well pumps
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