Three-phase asynchronous motors are widely used, but after long-term operation, various faults may occur. Timely identification of the cause of the fault and corresponding handling are important tasks to prevent the fault from escalating and to ensure the normal operation of the equipment. [b]I. The motor does not rotate after power is applied, but there is no abnormal noise, smell, or smoke.[/b] 1. Causes of the fault: ① Power supply not connected (at least two phases not connected); ② Fuse blown (at least two phases blown); ③ Overcurrent relay set too low; ④ Wiring error of control equipment. 2. Troubleshooting: ① Check the power circuit switch, fuse, and junction box for any breaks and repair them; ② Check the fuse model and cause of blown fuse and replace it with a new fuse; ③ Adjust the relay setting value to match the motor; ④ Correct the wiring. [b]II. The motor does not rotate after power is applied, and then the fuse blows.[/b] 1. Causes of the fault: ① One phase of power supply is missing, or one phase of the stator winding is reversed; ② Short circuit between phases of the stator winding; ③ Stator winding grounded; ④ Incorrect stator winding wiring; ⑤ Fuse cross-section too small; ⑥ Short circuit or grounding of the power supply line. 2. Troubleshooting ① Check if one phase of the disconnect switch is not properly closed, or if one phase of the power supply circuit is broken; eliminate reverse connection faults; ② Locate the short circuit point and repair it; ③ Eliminate grounding; ④ Locate the incorrect connection and correct it; ⑤ Replace the fuse; ③ Eliminate grounding point. [b]III. Motor does not turn after power-on but makes a humming sound[/b] 1. Causes of the fault ① Open circuit in the stator or rotor windings (one phase broken) or one phase of the power supply is lost; ② Incorrect connection at the beginning and end of the winding leads or reverse connection inside the windings; ③ Loose power supply circuit contacts with high contact resistance; ④ Overload of the motor or rotor jamming; ⑤ Low power supply voltage; ⑥ Small motor assembly is too tight or the grease in the bearing is too hard; ⑦ Seized bearing. 2. Troubleshooting ① Locate and repair the break point; ② Check the winding polarity; determine if the winding ends are correct; ③ Tighten loose wiring screws, use a multimeter to check for false connections at each joint, and repair accordingly; ④ Reduce load or find and eliminate mechanical faults; ⑤ Check if the specified face connection method is incorrectly connected as Y; check if the voltage drop is too large due to the power supply wire being too thin, and correct accordingly; ⑥ Reassemble to make it flexible; replace with qualified grease; ⑦ Repair bearings. [b]IV. Difficulty starting the motor, and the motor speed is significantly lower than the rated speed under rated load[/b] 1. Causes of the fault ① Low power supply voltage; ② Incorrectly connected as Y in face connection method; ③ Open weld or broken squirrel-cage rotor; ④ Incorrect or reversed connection of stator and rotor coils; ③ Adding too many turns when repairing the motor windings; ⑤ Motor overload. 2. Troubleshooting ① Measure the power supply voltage and try to improve it; ② Correct the connection method; ③ Check for open welds and break points and repair them; ④ Find the incorrect connection and correct it; ⑤ Restore the correct number of turns; ⑥ Reduce load. **V.** Unbalanced No-Load Current of Motor, Large Phase Difference Between Three Phases 1. Causes of Fault: ① Unequal number of turns in the three-phase stator windings during rewinding; ② Incorrect connection of the winding start and end points; ③ Unbalanced power supply voltage; ④ Faults such as inter-turn short circuits or reverse coil connections in the windings. 2. Troubleshooting: ① Rewind the stator windings; ② Check and correct; ③ Measure the power supply voltage and try to eliminate the imbalance; ④ Eliminate winding faults. **VI.** Unstable Ammeter Pointer, Swinging During No-Load and Overload of Motor 1. Causes of Fault: ① Open weld or broken bars in the squirrel-cage rotor; ② Fault in the wound rotor (one phase open circuit) or poor contact of the brush or slip ring short-circuit device. 2. Troubleshooting: ① Find and repair the broken bars or replace the rotor; ② Check and repair the rotor winding circuit. **VII.** Balanced No-Load Current of Motor, but Large Value 1. Causes of the fault: ① During repair, the number of turns in the stator winding was reduced too much; ② The power supply voltage was too high; ③ The Y-connected motor was mistakenly connected as Δ; ④ During motor assembly, the rotor was installed backwards, causing the stator core to be misaligned and the effective length to be shortened; ⑤ The air gap was too large or uneven; ⑥ When removing the old winding during major repairs, improper use of the hot disassembly method caused the core to burn out. 2. Troubleshooting: ① Rewind the stator winding to restore the correct number of turns; ② Try to restore the rated voltage; ③ Change the connection to Y; ④ Reassemble; ⑤ Replace with a new rotor or adjust the air gap; ⑤ Inspect the core or recalculate the winding, and appropriately increase the number of turns. [b]VIII. Abnormal noise during motor operation[/b] 1. Causes of the fault: ① The rotor rubs against the stator insulation paper or slot wedges; ② The bearings are worn or there are foreign objects such as sand in the oil; ③ The stator and rotor cores are loose; ④ The bearings are short of oil; ⑤ The air duct is blocked or the fan rubs against the fan cover; ⑥ The stator and rotor cores rub against each other; ⑦ The power supply voltage is too high or unbalanced; ⑧ The stator winding is incorrectly connected or short-circuited. 2. Troubleshooting ① Trim insulation and lower slot wedges; ② Replace or clean bearings; ③ Inspect stator and rotor cores; ④ Add oil; ⑤ Clean air ducts; reinstall devices; ⑥ Remove scratches, and if necessary, install a small rotor inside the machine; ⑦ Check and adjust power supply voltage; ⑧ Eliminate stator winding faults. [b]IX. Excessive Motor Vibration During Operation[/b] 1. Causes of Fault ① Excessive bearing clearance due to wear; ② Uneven air gap; ③ Rotor imbalance; ④ Bent shaft; ⑤ Deformed or loose core; ⑥ Unaligned coupling (pulley); ⑦ Unbalanced fan; ⑧ Insufficient strength of casing or foundation; ⑨ Loose motor foundation bolts; ⑩ Open circuit in squirrel-cage rotor; open circuit in wound rotor; stator winding fault. 2. Troubleshooting ① Inspect the bearings and replace them if necessary; ② Adjust the air gap to make it uniform; ③ Correct the rotor dynamic balance; ④ Straighten the shaft; ⑤ Correct the overlapping iron core; ⑥ Re-correct it to meet the specifications; ⑦ Inspect the fan, correct its balance and geometry; ⑧ Reinforce it; ⑨ Tighten the foundation bolts; ⑩ Repair the rotor winding; Repair the stator winding. [b]X. Bearing Overheating[/b] 1. Causes of the fault ① Too much or too little grease; ② Poor quality grease containing impurities; ③ Improper fit between the bearing and the journal or end cover (too loose or too tight); ④ The bearing inner hole is eccentric, rubbing against the shaft; ⑤ The motor end cover or bearing cover is not installed flat; ⑥ The coupling between the motor and the load is not aligned, or the belt is too tight; ⑦ The bearing clearance is too large or too small; ⑧ The motor shaft is bent. 2. Troubleshooting: ① Add grease as specified (1/3-2/3 of the volume); ② Replace with clean grease; ③ If too loose, repair with adhesive; if too tight, machine, grind the journal or end cover inner hole to fit properly; ④ Repair the bearing cover to eliminate rubbing points; ⑤ Reassemble; ⑥ Recalibrate and adjust belt tension; ⑦ Replace with a new bearing; ⑧ Align the motor shaft or replace the rotor. [b]XI. Motor overheating or even smoking[/b] 1. Causes of the fault: ① Excessive power supply voltage, causing a significant increase in core heating; ② Insufficient power supply voltage, coupled with the motor operating under rated load, resulting in excessive current and winding overheating; ③ Improper use of hot disassembly methods during winding repair, burning the core; ④ Friction between stator and rotor cores; ⑤ Motor overload or frequent starting; ⑥ Broken bars in the squirrel-cage rotor; ⑦ Phase loss in the motor, with two phases running; ⑧ Insufficient impregnation of the stator winding after rewinding; ⑨ High ambient temperature, excessive dirt on the motor surface, or blocked ventilation ducts; ⑩ Motor fan malfunction, resulting in poor ventilation; Stator winding faults (phase-to-phase, turn-to-turn short circuits; incorrect internal connections in the stator winding). 2. Troubleshooting: ① Reduce power supply voltage (e.g., adjust the tap changer of the power supply transformer). If the problem is caused by incorrect Y or Δ connection of the motor, correct the connection. ② Increase power supply voltage or replace with thicker power supply wires. ③ Inspect the iron core and eliminate the fault. ④ Eliminate rubbing points (adjust the air gap or press/machine the rotor). ⑤ Reduce load; control the start-up according to the specified number of times. ⑥ Inspect and eliminate rotor winding faults. ⑦ Restore three-phase operation. ⑧ Use secondary impregnation and vacuum impregnation processes. ⑨ Clean the motor, improve the ambient temperature, and take cooling measures. ⑩ Inspect and repair the fan, and replace it if necessary. Inspect the stator winding and eliminate the fault.