**Analysis of Common Faults in Electric Motors** Home > Bearing Knowledge > Analysis of Common Faults in Electric Motors *Created on 2018/5/16* var cpro_id = "u3440131";

Analysis of Common Faults in Electric Motors

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/*250*250 was created on 2017/12/25*/ var cpro_id = 'u3171089';

Three-phase asynchronous motors are widely used in industrial and commercial applications. However, after prolonged operation, various issues can arise. Timely identification of the root cause and appropriate troubleshooting are essential to prevent further damage and ensure smooth equipment operation. ### 1. Motor Does Not Start After Power On, No Noise or Smell **Causes:** - Power supply is not fully connected (at least two phases missing). - Fuses are blown (at least two phases affected). - Overcurrent relay settings are incorrect. - Wiring faults in control equipment. **Troubleshooting Steps:** - Check the power switch for any open circuits. - Inspect fuses and replace if necessary. - Adjust the overcurrent relay to match motor specifications. - Correct wiring connections. --- ### 2. Motor Does Not Rotate, Fuse Blows Immediately **Causes:** - Missing phase in power supply. - Stator windings short-circuited between phases. - Stator winding grounded. - Incorrect stator winding connection. - Blown fuse due to small cross-section. - Short circuit or grounding in power lines. **Troubleshooting Steps:** - Check for phase loss and correct it. - Locate and repair short-circuit points. - Eliminate ground faults. - Correct wiring errors. - Replace the fuse with a proper one. --- ### 3. Motor Does Not Turn After Power Is Applied **Causes:** - Open circuit in rotor winding or phase loss. - Winding leads connected incorrectly or internally reversed. - Loose contacts in the power circuit. - Excessive load or rotor jamming. - Low voltage supply. - Tight installation or hard grease in bearings. - Bearings stuck. **Troubleshooting Steps:** - Locate and fix the open circuit. - Check winding polarity and correct as needed. - Tighten loose connections and test with a multimeter. - Reduce load or address mechanical issues. - Ensure correct connection method (Y or Δ) and check wire thickness. - Lubricate bearings properly. - Repair or replace faulty bearings. --- ### 4. Motor Starts Difficultly, Speed Below Rated **Causes:** - Low supply voltage. - Incorrect Y-Δ connection. - Open welds or cracks in cage rotor. - Rotor winding misconnection or reversal. - Too many turns added during rewinding. - Motor overload. **Troubleshooting Steps:** - Measure and adjust supply voltage. - Correct the winding connection. - Repair or replace damaged rotor. - Reconnect or rewire the rotor correctly. - Re-wind the motor with correct number of turns. - Reduce load or improve cooling. --- ### 5. Unbalanced No-Load Current with Large Phase Differences **Causes:** - Unequal number of turns in stator windings. - Incorrect terminal connections. - Unbalanced power supply voltage. - Inter-turn short circuits or reversed coils. **Troubleshooting Steps:** - Rewind the stator with equal turns. - Check and correct terminal connections. - Balance the power supply voltage. - Remove winding faults such as shorts or reversed coils. --- ### 6. Unstable Ammeter Reading When Loaded **Causes:** - Broken or welded bars in the cage rotor. - Faulty winding or brush/collar ring contact issues. **Troubleshooting Steps:** - Detect and repair broken rotor bars. - Check and correct rotor circuit faults. --- ### 7. Balanced No-Load Current, But Value Is High **Causes:** - Excessively cut stator turns. - High supply voltage. - Incorrect Δ-Y connection. - Rotor misalignment or core deformation. - Large or uneven air gap. - Poor hot-break method during rewinding. **Troubleshooting Steps:** - Rewind the stator with correct number of turns. - Adjust supply voltage. - Change from Δ to Y if necessary. - Reinstall the motor correctly. - Adjust air gap or replace rotor. - Check and rework the iron core. --- ### 8. Abnormal Sounds During Operation **Causes:** - Rotor rubbing against stator insulation or wedges. - Worn bearings or foreign objects in lubricant. - Loose rotor core. - Lack of oil in bearings. - Fan or duct blockage. - Core rubbing. - Unbalanced or high voltage. - Winding faults. **Troubleshooting Steps:** - Trim insulation or remove wedges. - Replace or clean bearings. - Repair loose rotor core. - Add lubricant. - Clear air ducts and fan obstructions. - Fix core rubs. - Adjust voltage. - Repair winding issues. --- ### 9. Excessive Vibration During Operation **Causes:** - Worn bearings. - Uneven air gap. - Rotor imbalance. - Shaft bending. - Deformed or loose core. - Misaligned couplings or pulleys. - Unbalanced fan. - Weak base or casing. - Loose foot bolts. - Rotor winding faults. **Troubleshooting Steps:** - Repair or replace bearings. - Adjust air gap. - Balance the rotor. - Straighten the shaft. - Align the core. - Align couplings. - Balance the fan. - Reinforce the structure. - Tighten bolts. - Repair both rotor and stator windings. --- ### 10. Bearing Overheating **Causes:** - Excessive or insufficient lubrication. - Poor-quality oil with impurities. - Incorrect bearing fit with journal or housing. - Bearing inner race friction. - Non-flat end cover or bearing cap. - Misaligned coupling or tight belt. - Excessive bearing clearance. **Troubleshooting Steps:** - Apply the correct amount of lubricant (1/3–2/3 of volume). - Replace with clean lubricant. - Adjust bearing fit by grinding or replacing. - Repair bearing caps. - Reinstall properly. - Adjust belt tension. - Replace bearings if necessary. - Align the motor shaft. --- ### 11. Motor Overheats and Smokes **Causes:** - High or low supply voltage. - Overloaded motor or excessive current. - Improper hot-break method during rewinding. - Rotor core rubbing. - Overload or frequent starts. - Cracked rotor bars. - Phase loss. - Inadequate insulation paint. - High ambient temperature or dust. - Fan or ventilation problems. - Winding faults. **Troubleshooting Steps:** - Adjust voltage or correct Y/Δ connection. - Improve power supply or use thicker wires. - Repair the core. - Eliminate rubbing points. - Reduce load or limit start frequency. - Repair rotor bars. - Restore three-phase operation. - Use proper insulation methods. - Clean the motor and improve cooling. - Repair or replace the fan and fix winding issues. --- **Related Bearing Knowledge:** Rolling bearing selection, imported bearing layout, classification, fan bearing fault analysis, replacement techniques, and more. 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