Analysis of common faults in three-phase asynchronous motors

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Three-phase asynchronous motors are widely used; however, after prolonged operation, various faults may occur. Promptly identifying the causes of these faults and taking appropriate measures is a crucial task for preventing the escalation of faults and ensuring the normal operation of the equipment. 　　 　　I. The motor does not rotate after power is applied, but there are no abnormal noises, no unusual odors, and no smoking. 　　　1. Causes of the fault: ① Power supply not connected (at least two phases are not connected) ； ②Fuse blowout (at least two phases blown) ； ③The overcurrent relay is set too low ； ④Wrong wiring of the control device. 　　 　　2. Troubleshooting: ① Check the power circuit switches, fuses, and wiring boxes for any breaks, and repair them ； ②Check the fuse model and the reason for blowing, then replace it with a new fuse ； ③Adjust the relay setting value in coordination with the motor ； ④Correct the wiring. 　　 　　II. After power is applied, the motor does not rotate, and then the fuse blows.
1. Causes of the fault: ① One phase of the power supply is missing, or one phase of the stator winding is connected reversely ； ②Inter-phase short circuit in stator windings ； ③Stator winding grounding ； ④Incorrect stator winding connection ； ⑤The fuse cross-section is too small ； ⑤The power cable is short-circuited or grounded. 　　 　　2. Troubleshooting ① Check whether one phase of the disconnector has not been properly closed; there might be an open circuit in one phase of the power supply circuit ； Eliminate reverse connection faults ； ②Identify the short circuit point and repair it ； ③Eliminate grounding ； ④Identify any incorrect connections and correct them ； ⑤Replace the fuse ； ③Remove the ground point. 　　 　　III. After power is applied, the motor does not rotate but makes a humming sound
1. Causes of the fault: ① Open circuit in the stator or rotor windings (one phase broken) or loss of power in one phase of the supply ； ②The start and end of the winding leads are connected incorrectly, or the wires inside the winding are reversed ； ③The power supply circuit contacts are loose, resulting in high contact resistance ； ④The motor is under excessive load or the rotor is stuck ； ⑤The power supply voltage is too low ； ⑥The small electric motor is assembled too tightly, or the grease in the bearings is too hard ； ⑦The bearing is stuck. 　　 　　2. Troubleshooting ① Identify the fault point and fix it ； ②Check winding polarity ； Determine whether the winding ends are correct ； ③Tighten any loose wiring screws, and use a multimeter to check whether the connections are proper; make repairs if necessary ； ④Reduce the load or identify and eliminate mechanical faults; ⑤ Check whether the specified wiring method has been mistakenly connected in a Y configuration ； Was the excessive voltage drop caused by overly thin power cables? Correct it; ⑥ Reassemble it to ensure flexibility ； Replace with qualified grease ； ⑦Repair the bearing. 　　 　　IV. The motor has difficulty starting, and at its rated load its speed is significantly lower than the rated speed. 1. Causes of the fault: ① Low supply voltage ； ②Motor connected in Y configuration due to interview method error ； ③Welding failure or breakage of the cage rotor ； ④Local coil misconnection or reversal of the stator and rotor ； ③Too many turns were added when repairing the motor windings ； ⑤Motor overload. 　　 　　2. Troubleshooting ① Measure the power supply voltage and try to improve it ； ②Correct the wiring ； ③Check for weld cracks and breaks and repair them ； ④Identify the incorrect connection points and make corrections ； ⑤Restore the correct number of turns ； ⑥Unload. 　　 　　V. Unbalanced no-load current in the motor, with large differences between the three phases 　　　1. Causes of the fault: ① During rewinding, the number of turns in the stator’s three-phase windings is not equal ； ②The ends of the winding are connected incorrectly ； ③Unbalanced power supply voltage ； ④There are faults in the windings such as inter-turn short circuits and reversed coil connections. 　　 　　2. Troubleshooting ① Rewind the stator windings ； ②Check and correct ； ③Measure the power supply voltage and try to eliminate the imbalance ； ④Eliminate winding faults. 　　 　　VI. When the motor is running under no-load or overload conditions, the ammeter pointer becomes unstable and oscillates. 　　　1. Causes of the fault: ① Welding failure or breakage of the bars in the squirrel-cage rotor ； ②Wound-rotor fault (one-phase open circuit) or poor contact of the brush and slip ring short-circuiting devices. 　　 　　2. Troubleshooting ① Identify the broken bar and repair it or replace the rotor ； ②Inspect the rotor winding circuit and repair it. 　　 　　VII. The no-load current of the motor is balanced, but its value is high.
1. Causes of the fault: ① During repair, the number of turns in the stator winding was reduced excessively ； ②The power supply voltage is too high ； ③Y-connected motor mistakenly connected as Δ ； ④During motor assembly, the rotor was installed in the wrong direction, causing the stator core to be misaligned and its effective length to decrease ； ⑤Excessively large or uneven air gap ； ⑥During major repairs, when removing the old windings, improper use of thermal removal methods caused damage to the core by overheating. 　　 　　2. Troubleshooting ① Rewind the stator windings to restore the correct number of turns ； ②Try to restore the rated voltage ； ③Change to Y connection ； ④Reassembly ； ③Replace the rotor or adjust the air gap ； ⑤Inspect the core or recalculate the windings, increasing the number of turns as appropriate. 　　 　　VIII. Abnormal noises are heard when the motor is in operation; there are unusual sounds. 1. Causes of the fault: ① Friction between the rotor and the insulating paper or slot wedges in the stator ； ②Bearing wear or foreign particles such as sand in the oil ； ③Loose stator and rotor cores ； ④Bearings lack oil ； ⑤Duct blockage or fan rubbing against the shroud, ⑥ contact between the stator and rotor cores ； ⑦Supply voltage is too high or unbalanced ； ⑧The stator windings are misconnected or short-circuited. 　　 　　2. Troubleshooting ① Trim the insulation and reduce the groove wedge ； ②Replace or clean the bearings ； ③Inspection of stator and rotor cores ； ④Keep going! ； ⑤Clean the air ducts ； Reinstall the device ； ⑥Remove scratches; use a small rotor inside the vehicle if necessary ； ⑦Check and adjust the power supply voltage ； ⑧Eliminate stator winding faults. 　　 　　IX. Excessive vibration of the motor during operation 　　　1. Causes of the fault: ① Excessively large bearing clearance due to wear ； ②Uneven air gap ； ③Rotor imbalance ； ④The rotating shaft is bent ； ⑤Core deformation or loosening ； ⑥The center of the coupling (pulley) is not aligned ； ⑦Unbalanced fan ； ⑧The strength of the casing or foundation is insufficient ； ⑨The motor’s foot screws are loose ； ⑩Open weld and circuit breakage in the cage rotor ； Open circuit in wound rotor ； Stator winding fault. 　　 　　2. Troubleshooting ① Inspect the bearings; replace them if necessary ； ②Adjust the air gap to make it uniform ； ③Correct rotor dynamic balance ； ④Aligning shaft ； ⑤Correct the overlapping cores; ⑥ Recorrect them to meet the specifications ； ⑦Service the fan, adjust its balance, and correct its geometry ； ⑧Perform reinforcement ； ⑨Tighten the foot screws ； ⑩Repair rotor windings ； Repair the stator windings. 　　 　　X. Bearing Overheating 　　 　1. Causes of the fault: ① Excessive or insufficient grease ； ②The oil quality is poor and contains impurities ； ③Improper fit between the bearing and the shaft journal or end cover (too loose or too tight) ； ④The inner bore of the bearing is eccentric, causing it to rub against the shaft ； ⑤The motor end cover or bearing cover is not properly installed ； ⑥The coupling between the motor and the load is not adjusted, or the belt is too tight ； ⑦The bearing clearance is either too large or too small ； ⑧The motor shaft is bent. 　　 　　2. Troubleshooting ① Apply grease as specified (1/3–2/3 of the volume) ； ②Replace with clean lubricating grease ； ③If it is too loose, it can be repaired with an adhesive; if it is too tight, machining is required – the shaft journal or the inner hole of the end cover must be machined to fit properly ； ④Repair the bearing cover to eliminate the rubbing points ； ⑤Reassembly ； ⑥Re-calibrate and adjust the belt tension ； ⑦Replace with new bearings ； ⑧Correct the motor shaft or replace the rotor. 　　 　　XI. Overheating of the motor or even smoking 　　　1. Causes of the fault: ① Excessively high supply voltage, which leads to increased heating of the core** ； ②The power supply voltage is too low; the motor is operating under its rated load, and the high current causes the windings to overheat ； ③When repairing and removing windings, improper use of thermal disassembly methods caused the core to be burned ； ④The stator and rotor cores rub against each other ； ⑤Motor overload or frequent starting ； ⑥Broken bars in cage rotor ； ⑦Motor has a missing phase, operating on two phases ； ⑧It is scheduled that the winding will not be adequately impregnated after rewinding ； ⑨High ambient temperature, excessive dirt on the motor surface, or blocked ventilation channels ； ⑩Motor fan failure, poor ventilation ； Stator winding faults (phase-to-phase, turn-to-turn short circuits ； Incorrect internal connection of the stator windings). 　　 　　2. Troubleshooting ① Reduce the power supply voltage (e.g., by adjusting the tap of the power supply transformer); if the issue is caused by an incorrect Y or Δ connection of the motor, then the connection should be corrected ； ②Increase the power supply voltage or use thicker power cables ； ③Inspect the core and eliminate the fault ； ④Eliminate rubbing points (adjust the air gap or grind/machine the rotor) ； ⑤Unload ； Control the startups according to the specified number of times ； ⑥Check and eliminate rotor winding faults ； ⑦Restore three-phase operation ； ⑧Secondary dipping and vacuum dipping processes are employed ； ⑨Clean the motor, improve the ambient temperature, and implement cooling measures ； ⑩Inspect and repair the fan; replace it if necessary ； Inspect and repair the stator windings to eliminate the fault.