Analysis and treatment of common faults in the dri

2022-09-19
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Analysis and treatment of common faults of mill drive system

in the mill drive system of small and medium-sized cement production enterprises, high-voltage wound asynchronous motors use frequency sensitive rheostat to reduce voltage and start a wide range of control forms. However, because the production environment of the system is generally poor, the mill load is large, and most of them are started under heavy load, the starting current is large, and the peak maintenance time is long. In addition, due to improper site management, use and maintenance, hidden dangers cannot be found in time or proper measures cannot be taken to eliminate, resulting in further expansion of the accident, resulting in a large proportion of shutdown accidents. The author takes the four 6000V, 380 ~ 630kw wound asynchronous motors used by our company and the common faults of their systems in the production process as an example to make a superficial analysis and summary, and puts forward the corresponding treatment methods and preventive measures

1 frequency sensitive rheostat is heated or one phase is burnt out

cause analysis: the main cause of frequency sensitive rheostat heating is that the time relay action setting time is too long or the time relay refuses to operate after starting, and the AC contactor cannot be switched in time, so that the frequency sensitive rheostat cannot be removed from the starting circuit in time and is in the starting state for a long time. The repaired frequency sensitive rheostat should consider whether the number of turns of the wire package and the cross-section of the wire are correct. Under the above reasons, the group of frequency sensitive rheostats with relatively weak insulation is overheated and burned out. In serious cases, two or even three groups can be burned out at the same time

treatment and prevention: according to the load situation, reasonably determine the switching action time of the time relay, frequently check the contact condition of the AC contactor to ensure that the contact area and contact pressure are balanced appropriately, and check the action condition of each relay to prevent the contact and contact from melting and bonding. Set the overheat and overcurrent protection device well, and test the setting value on schedule to ensure that the mechanism acts sensitively and reliably

2 rolling bearing heating

rolling bearing heating, which will cause motor locked rotor and stuck in serious cases; The sliding bearing is heated, causing alloy sticking and melting (Bush burning) in serious cases

cause analysis: in particular, we should mention the excessive grease of new materials; The clearance between the roller and the inner and outer sleeves is too large, the bearing body is pitted or stripped, the inner and outer sleeves rotate, and the cage is damaged. The bearing bush cannot be scraped and grinded well, and the contact surface of the shaft and Bush is small; The clearance between bearing bush and journal is too small or too large; Oil cut-off or inflexible operation of oil ring, unable to bring enough lubricating oil; The wrong brand of lubricating grease or impurities in the oil destroy the formation of oil film; Those who implement forced mechanical oil supply may also mix oil and water due to the leakage of water cooler, and the physical properties of grease will be damaged

treatment and prevention: when the rolling bearings are newly installed or cleaned, they must be cleaned with gasoline or diesel oil. It is necessary to consider whether the faults in the refrigeration system are clean. After they are dry, they can be filled with qualified lubricating grease of the specified brand. The filling of lubricating grease should not be too full. It is appropriate to fill 1/2 of the cavity of the secondary electric machine, and 1/2 ~ 1/3 of the cavity of the motor above the secondary electric machine. The rolling bearings shall be inspected regularly, and the above abnormal symptoms shall be replaced in time. At the same time, the sealing shall be strengthened in daily maintenance, the oil shall be changed regularly, and the bearing cover and motor end cover shall be installed in place. When installing the rolling bearings with large journals, they can be boiled in the engine oil of < 110 ℃ and then hot installed to prevent bearing damage and journal strain. For the unexplained temperature rise of the bearing, the wear of the alloy bearing should be checked in time to ensure that the oil line is unblocked. The contact point should not be less than 6 points per square centimeter, the contact surface between the journal and the bearing bush should not be less than 80%, and the vertical line along the radial direction of the bearing should not be less than 35 °. Fit clearance between journal and bearing bush: the alloy bush is 1 ‰ of the journal, and the wear limit is not greater than 4 ‰; The copper bush is 1.2 ‰ of the journal, and the wear limit is not greater than 5 ‰. The fitting clearance shall not be too large or too small. If it is too small, it shall be scraped and grinded again. If it is too large, it shall be scraped and grinded according to the standard after replacing the new tile or re hanging the alloy. If there is insufficient oil in the oil ring, forced mechanical oil supply can be implemented to make up for it, and oil cut-off phenomenon can be eliminated. Use qualified lubricating grease according to the design requirements, replace the grease in winter and summer according to the regulations, and seal well to prevent dirt, dust and debris from mixing into the lubricating oil. When reusing the replaced grease, filter and test it to ensure that its physical properties meet the requirements of the standard. Regularly check the service condition of the water cooler to prevent leakage caused by corrosion

3 noise and vibration increase

during the operation of the motor, the noise and vibration increase, and the pointer of the ammeter swings back and forth

cause analysis: the clearance between the roller of rolling bearing and the inner and outer sleeves is too large, the bearing body is pitted or stripped, the cage is damaged, and the inner and outer sleeves rotate; The fit clearance between bearing bush and journal is too large; Rotor unbalance; One phase brush has poor contact or open circuit

treatment and prevention: the treatment and prevention measures for faults caused by bearings are the same as those described in article "2". In production, the rotor imbalance is mostly damaged by mechanical force, the wind wing is broken, or the rotor is bent due to centrifugal force and long-term vibration due to excessive bearing and bearing bush clearance. The wind wing can be broken and shut down for welding, and the rotor bending imbalance is generally difficult for manufacturers to deal with. Check and adjust the brush pressure and contact area, especially for Xin'an 5 Argo, which will provide convenient financial services for 'partners'. Install the brush after grinding to ensure that the contact area of each brush is not less than 90%, and prevent the brush from breaking

4 brush ignition

brush ignition, brush braid burning red or burnt out

cause analysis: there are dirt or burn marks on the surface of the slip ring, causing the surface to be out of round or smooth, and the contact area and pressure of the brush are sometimes large and sometimes small; Improper or uneven brush pressure; The brand of electric brush is improper. Because the column and beam built with steel structure are narrower and thinner than that of conventional concrete, the contact surface is small, and the carrying capacity is not enough; The electric brush has poor follow-up performance in the brush box

treatment and prevention: pay attention to clean the dirt and polish the burn marks on the surface of the slip ring with a fine abrasive cloth above 120 to ensure good contact between the brush and it. Regularly check and adjust the brush pressure to a balanced and appropriate position to prevent uneven pressure tightness. Select the brand and size of the brush according to the design requirements of the original manufacturer to ensure that the contact area and current carrying capacity of the brush meet the requirements. Clean the brush box or slightly shrink the brush to make it move freely in the brush box

5 rotor lead wire nose burned out

cause analysis: the current carrying capacity of the wire nose is small; Loose due to vibration or loose crimping during wiring, causing local contact resistance to increase and heat

treatment and prevention: this problem is more intuitive. As long as you pay attention to the selection of appropriate material and section of the wiring nose and pay attention to regular inspection, you can eliminate the vibration source in time to prevent the joint from oxidation and loosening

6 open welding and tin throwing at the end of rotor winding cause open circuit or grounding

cause analysis: due to damp insulation, aging, cement dust

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