11 common faults and repair methods of three-phase asynchronous motors

1. The motor makes abnormal noises when running. There are abnormal noises.

 

1. cause of issue

① The rotor rubs against the stator insulation paper or slot wedge;

② Bearing wear or foreign matter such as sand in the oil;

③The stator and rotor cores are loose;

④The bearing is short of oil;

⑤ Air duct filling or fan wiping cover;

⑥The stator and rotor cores rub against each other;

⑦The power supply voltage is too high or unbalanced;

⑧The stator winding is misconnected or short-circuited.

 

2. troubleshooting

① Trim the insulation and lower the groove wedge;

②Replace the bearings or clean the bearings;

③Inspect stator and rotor cores;

④Come on;

⑤Clean the air duct; reinstall the device;

⑥Eliminate scratches, and if necessary, remove the small rotor in the car;

⑦ Check and adjust the power supply voltage;

⑧ Eliminate stator winding faults.

 

2. The motor vibrates greatly during operation.

 

1. cause of issue

①The bearing clearance is too large due to wear;

②The air gap is uneven;

③The rotor is unbalanced;

④The rotating shaft is bent;

⑤The iron core is deformed or loose;

⑥The center of the coupling (pulley) is not corrected;

⑦The fan is unbalanced;

⑧The chassis or foundation is not strong enough;

⑨The motor anchor screws are loose;

⑩ The cage rotor is open and disconnected; the wound rotor is open; and the stator winding is faulty.

 

2. troubleshooting

①Inspect the bearings and replace them if necessary;

②Adjust the air gap to make it uniform;

③Correct rotor dynamic balance;

④ Straighten the rotating shaft;

⑤Correction of overlapping cores;

⑥Recalibrate to make it comply with regulations;

⑦Inspect the fan, correct the balance, and correct its geometric shape;

⑧Reinforcement;

⑨Tighten the anchor screws;

⑩Repair the rotor winding; repair the stator winding.

 

3. The motor cannot rotate after power is supplied, but there is no abnormal sound, odor or smoke.

 

1. cause of issue

①The power supply is not connected (at least two phases are not connected);

②The fuse is blown (at least two phases are blown);

③The overcurrent relay is adjusted too small;

④The control equipment wiring is wrong.

 

2. troubleshooting

① Check the power circuit switch, fuse, and junction box for breakpoints and repair them;

② Check the fuse model and the reason for the fuse, and replace it with a new one;

③Adjust the relay setting value to match the motor;

④ Correct the wiring.

 

4. The motor does not rotate after power is supplied, and then the fuse burns out.

 

1. cause of issue

① One phase of power supply is missing, or one phase of the fixed main coil is connected;

②The stator windings are short-circuited between phases;

③The stator winding is grounded;

④The stator winding wiring is wrong;

⑤The fuse cross-section is too small;

⑥The power cord is short-circuited or grounded.

 

2. troubleshooting

① Check whether one phase of the knife switch is not closed properly, but one phase of the power circuit is disconnected; eliminate the reverse connection fault;

② Find the short circuit point and repair it;

③ Eliminate grounding;

④ If a misconnection is detected, correct it;

⑤Replace the fuse;

⑥ Eliminate the grounding point.

 

5. The motor does not rotate and makes a buzzing sound after power is supplied.

 

1. cause of issue

① The stator and rotor windings are open circuited (one phase is disconnected) or one phase of the power supply is out of power;

② The start and end of the winding lead wire are connected incorrectly or the internal connections of the winding are reversed;

③The contacts of the power circuit are loose and the contact resistance is high;

④The motor load is too large or the rotor is stuck;

⑤The power supply voltage is too low;

⑥The assembly of the small motor is too tight or the grease in the bearing is too hard;

⑦The bearing is stuck.

 

2. troubleshooting

① Identify breakpoints and fix them;

② Check the winding polarity; determine whether the winding ends are correct;

③Tighten the loose wiring screws, use a multimeter to determine whether each joint is falsely connected, and repair it;

④ Reduce load or detect and eliminate mechanical faults;

⑤ Check whether the specified Δ connection is mistakenly connected to Y; whether the voltage drop is too large due to the power wire being too thin, correct it;

⑥Reassemble to make it flexible; replace qualified grease;

⑦Repair the bearing.

 

6. The no-load current of the motor is unbalanced, and there is a big difference between the three items.

 

1. cause of issue

① When rewinding, the number of turns of the three-phase winding of the stator is not equal;

②The first and last ends of the winding are connected incorrectly;

③Unbalanced power supply voltage;

④The winding has faults such as inter-turn short circuit and coil reverse connection.

 

2. troubleshooting

①Rewind the stator winding;

② Check and correct;

③Measure the power supply voltage and try to eliminate the imbalance;

④ Eliminate winding faults.

 

7. When the motor is no-load or overloaded, the ammeter pointer is unstable and swings.

 

1. cause of issue

① The cage rotor guide bars are open or broken;

② The wound rotor is faulty (one phase is open) or the brushes and slip ring short-circuit devices have poor contact.

 

2. troubleshooting

① If the broken bar is found, repair it or replace the rotor;

② Check the rotor circuit and repair it.

 

8 The no-load current of the motor is balanced, but the value is large

 

1. cause of issue

① During repair, the number of turns of the stator winding is reduced too much;

②The power supply voltage is too high;

③The Y connection to the motor is mistakenly connected to Δ;

④ During motor assembly, the rotor is installed backwards, causing the stator core to be misaligned and the effective length to be shortened;

⑤The air gap is too large or uneven;

⑥ When dismantling old windings for overhaul, improper hot removal method is used, causing the iron core to be burned.

 

2. troubleshooting

①Rewind the stator winding to restore the correct number of turns;

② Try to restore the rated voltage;

③Change to Y;

④Reassembly;

⑤Replace the rotor with a new one or adjust the air gap;

⑥Inspect the iron core or recalculate the winding and increase the number of turns appropriately.

 

9. It is difficult to start the motor. At rated load, the speed is much lower than the rated speed.

 

1. cause of issue

①The power supply voltage is too low;

②Δ connection method: the motor is mistakenly connected to Y;

③The cage rotor is welded or broken;

④The local coils of the stator and rotor are connected incorrectly or reversely;

⑤ Increase the number of turns too much when repairing the motor winding;

⑥The motor is overloaded.

 

2. troubleshooting

①Measure the power supply voltage and try to improve it;

②Correct the connection method;

③Check open welding and breakpoints and repair them;

④ Detect misconnections and correct them;

⑤Restore the correct number of turns;

⑥Load reduction.

 

10The motor overheats or even smokes

 

1. cause of issue

①The power supply voltage is too high, which greatly increases the heating of the iron core;

②The power supply voltage is too low, the motor is running with rated load, and the current is too high, causing the windings to heat up;

③When repairing and dismantling the winding, improper hot removal method is used, which may burn the iron core;

④The stator and rotor cores rub against each other;

⑤The motor is overloaded or starts frequently;

⑥Broken cage rotor bars;

⑦The motor is missing a phase and runs on two phases;

⑧After rewinding, the winding is not fully impregnated with paint;

⑨The ambient temperature is high, there is a lot of dirt on the surface of the motor, or the ventilation duct is blocked;

⑩ Motor fan failure, poor ventilation; stator winding failure (short circuit between phases and turns; incorrect internal connection of the stator winding).

 

2. troubleshooting

① Reduce the power supply voltage (such as adjusting the tap of the power supply transformer). If it is caused by incorrect connection of motor Y and Δ, the connection should be corrected;

②Increase the power supply voltage or replace the thick power supply wire;

③Inspect the iron core and troubleshoot;

④ Eliminate friction points (adjust the air gap or set the rotor);

⑤Load reduction; control starting according to specified times;

⑥ Check and eliminate rotor winding faults;

⑦Restore three-phase operation;

⑧Adopt secondary dipping and vacuum dipping processes;

⑨Clean the motor, improve the ambient temperature, and adopt cooling measures;

⑩ Check and repair the fan, replace if necessary; inspect the stator winding to eliminate faults.

 

11Motor bearing overheating

 

1. cause of issue

① Too much or too little grease;

②The oil is of poor quality and contains impurities;

③ Improper cooperation between the bearing and the journal or end cover (too loose or too tight)

④The inner hole of the bearing is eccentric and rubs against the shaft;

⑤The motor end cover or bearing cover is not installed flatly;

⑥The coupling between the motor and the load is not corrected, or the belt is too tight;

⑦The bearing clearance is too large or too small;

⑧The motor shaft is bent.

 

2. troubleshooting

①Add grease as required (1/3-2/3 of the volume);

②Replace with clean grease;

③If it is too loose, it can be repaired with adhesive. If it is too tight, it should be turned on and the inner hole of the journal or end cover should be ground to make it suitable;

④Repair the bearing cap to eliminate friction spots;

⑤Reassembly;

⑥Recalibrate and adjust the belt tension;

⑦Replace with new bearings;

⑧Correct the motor shaft or replace the rotor.