Causes and Countermeasures of Common Motor Failures

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Low-voltage three-phase AC squirrel-cage motors (hereinafter referred to as motors) have the advantages of simple structure, low price, and easy maintenance. Therefore, it is widely used in the driving devices of industrial and agricultural machinery and equipment, and is the most widely used of all electric motors. Despite this, various faults will inevitably occur in the motor during actual operation. Below, the causes and countermeasures for common motor failures are analyzed for reference by peers. 1. The motor temperature rises too high or smoke is a symptom of motor overheating. There are many reasons: There are factors external to the motor (such as poor power supply quality, excessive load, high ambient temperature, poor ventilation, etc.) ； There are also reasons for the motor itself. Common causes and countermeasures of the motor itself: 1. The winding connection method is wrong, and the star is mistakenly connected to a delta or vice versa. 2. The stator winding turns or phases are short-circuited or grounded, which increases the current and increases the copper loss. If the fault is not serious, it only needs to be re-insulated. If it is serious, the winding should be replaced. 3. One phase winding of the stator is disconnected, or one branch of the parallel winding is disconnected, causing an imbalance in the three-phase current and causing the winding to overheat. 4. The rotor is broken. The copper bar rotor should be repaired or replaced by welding, and the cast aluminum rotor should be replaced. 5. The stator and rotor rub against each other. You can check whether the bearings are loose and whether the stator and rotor are poorly assembled. 2. Bearing overheating: When the temperature of the rolling bearing of the motor exceeds 95°C and the temperature of the sliding bearing exceeds 80°C, the bearing is overheated. The reasons and countermeasures are as follows: 1. Bearings that are damaged should be replaced with new ones. 2. There is too little or too much grease in the rolling bearing or there are impurities such as iron filings. The capacity of the grease should not exceed 70% of the volume of the bearing and bearing cap. If there are impurities, it should be replaced with new ones. 3. The fit between the bearing and the end cover is too tight or too loose. If it is too tight, process the bearing chamber; if it is too loose, insert a steel sleeve into the end cover. 4. The two end covers or bearing covers of the motor are poorly assembled. Install the end cover or bearing cover flat and tighten the screws. 5. The transmission belt is too tight or the coupling is poorly assembled. Adjust the belt tension and calibrate the coupling. 6. There is too little lubricating oil in the sliding bearing, there are impurities or the oil ring is stuck. It should be refueled, replaced with new oil, and the oil ring should be repaired or replaced. 3. Abnormal noise 1. When the stator and rotor rub against each other, a harsh "chacha" sound will be produced. Bearings should be inspected and damaged ones replaced. If the bearing is not damaged and the inner or outer ring of the bearing is found, the bearing and end cover can be replaced or the bearing and end cover can be replaced. 2. The motor runs with phase loss and the roar is extremely loud. You can cut off the power and then close it again to see if it can start normally again. If it cannot start, one phase may be open. Phase loss operation will also occur if the contacts of the switch and contactor are not connected. 3. When the bearing is seriously short of oil, a "hissing" sound can be heard from the bearing chamber. Bearings should be cleaned and new oil added. 4. The fan blades will make impact sounds when they hit the shell or have debris. The fan blades should be corrected and debris around the fan blades should be removed. 5. The rotor guide bar is broken, a high and low "buzzing" sound occurs, the rotation speed also slows down, and the current increases. 6. The first and end connections of the stator winding are incorrectly connected, causing a low roar and a decrease in rotational speed. 4. Excessive vibration 1. The motor rotor is unbalanced (such as the counterweight screw on the rotor falls off) and the dynamic balance should be corrected. 2. The transmission pulley is unbalanced and the static balance should be corrected. 3. The rotating shaft is bent. The rotating shaft should be replaced, or the sleeve should be machined (hot sleeve). 4. The installation foundation is uneven or unstable. It should be reinstalled and fixed smoothly. 5. The rotor guide bars are broken, causing the load current to oscillate intermittently. 6. The coupling is not assembled correctly or is loose. 7. The driven machinery loses its dynamic balance. 8. There is a local fault in the stator winding, and the rotating magnetic field is unbalanced and causes vibration. 5. Three-phase current imbalance caused during operation 1. The three-phase power supply voltage is seriously unbalanced (that is, not equal). Such as poor contact of switch contacts, etc. 2. One phase of the three-phase winding is open circuit or one phase fuse is blown, causing phase loss operation. 3. There is a partial short circuit between winding turns or phases, but the fuse is not broken. 4. One parallel branch or several parallel branches of a certain group of three-phase windings are disconnected, causing the three-phase impedance to be unequal. 5. The first and end ends of one phase in the three-phase stator winding are wrong, but the fuse is not blown. 6. When the motor is running, the ammeter pointer swings back and forth. The cause of this fault is likely to be an open circuit of the rotor bar. 7. The motor speed becomes low 1. The power supply voltage is too low. Check and find out the cause. 2. If the rotor guide bar is broken or desoldered, the broken bar should be inspected and repaired. 3. The stator winding connection is wrong, the connection should be checked and corrected. 4. If the load is too large, the load should be reduced or the motor power should be increased. 5. Excessive bearing wear causes the stator and rotor to rub against each other. 8. Difficulty in starting or failure to start at all 1. The stator winding or rotor winding is open circuit. 2. If the stator winding is short-circuited between phases or grounded, you can check it with a megger. 3. The stator winding is connected incorrectly, or the start and end of one phase winding are connected in reverse, which should be checked and corrected. 4. Scan the stator and rotor. 5. If the bearing is damaged or stuck, the bearing should be replaced. 9. The fuse is blown during startup 1. One-phase power supply is disconnected and started with heavy load. 2. The fuse is too thin or is mechanically damaged during installation (the cross-section becomes smaller). 3. Overload. 4. One phase of the stator winding is open circuit. 5. The stator winding or rotor winding is seriously short-circuited or grounded. 6. The repaired motor has one phase end connected reversely or some internal coils connected reversely. 10. The motor casing is charged 1. The insulation of the lead wire is damaged and the motor casing hits the casing. 2. The winding insulation is damaged due to moisture and the shell hits. 3. The motor is overloaded for a long time, and the winding insulation ages and cracks, causing the motor to hit the shell. 4. The insulation of the notches at both ends is damaged or the wires are loose, the iron core silicon steel sheet is not pressed tightly or has spikes, etc., and the wires are scratched during vibration. 5. There are iron filings and other debris in the groove, and the wires are scratched and hit the shell when they are inserted. 6. When embedding wires, the wire insulation is mechanically damaged and hits the shell. 7. The stator and rotor cores rub against each other, causing the core to overheat and burn the slot wedge and insulation, causing the coil to hit the shell. 8. Poor grounding, causing the protective grounding to fail. 11. Almost half of the motor burns caused by phase loss operation are caused by the motor phase loss operation. The main reasons for phase loss operation are as follows: 1. If one phase of the main power line is powered off due to failure of other equipment, the other three-phase equipment connected to the power line will operate with a lack of phase. 2. The one-phase fuse has poor contact (such as the screws are not tightened), the fuse is severely oxidized, or is mechanically damaged (especially man-made damage during installation), causing the one-phase fuse to blow out prematurely. 3. One phase of the blade or contact of the starting equipment is in poor contact or is not in contact, such as the contact is burned or loose. 4. One phase winding of the motor is open circuit, or one phase connector in the junction box is loose. It can be seen that there are many types of motor faults during operation. Although some fault phenomena are very similar, the causes are different. Therefore, only by deeply understanding and understanding the real cause of motor failure can we quickly take effective countermeasures to eliminate motor faults.