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

In our daily work, there are many kinds of situations that cause the failure of three-phase asynchronous motor, below we list the main 11 common faults and repair methods

The sound of the motor is not normal when running, there is a strange noise

1. Cause of fault
   ① due to wear bearing clearance is too large.
   ② uneven air gap.
   ③unbalanced rotor.
   ④bending of the rotor shaft.
   ⑤ deformation or loosening of the iron core.
   (vi) Coupling (pulley) centre not corrected.
   (vii) Fan unbalance; (viii)
   ⑧Insufficient strength of the housing or foundation
   ⑨ Loose motor foot screws
   ⑩Cage rotor open weld break; wire-wound rotor break; plus stator winding fault.
2. Troubleshooting
   ① Overhaul the bearing, replace if necessary.
   ② adjust the air gap to make it even.
   ③Calibrate the rotor dynamic balance.
   ④ straighten the rotor shaft.
   ⑤ Correct the overlapping iron core.
   (6) Recalibrate to conform to regulations.
   (vii) Overhaul the fan, correct the balance and correct its geometry.
   ⑧ Reinforcement.
   ⑨ tighten the foot screws.
   ⑩ Repair the rotor winding; repair the stator winding.

The motor cannot rotate after power is applied, but there is no strange noise, no smell and no smoke

1. Cause of failure
   ① Power is not on (at least two phases are not on).
   ②Fuse fused (at least two phases fused)
   ③Overcurrent relay is set too small.
   ④The control equipment is incorrectly wired.
2. Troubleshooting
   ①Check the power circuit switch, fuse, junction box at whether there are broken points, repair.
   ②Check the fuse type and the reason for fusing, and replace the fuse with a new one.
   ③Adjust the relay adjustment value to match the motor.
   ④ Correct the wiring.

The motor does not rotate after power is applied, then the fuse burns out

1. Cause of failure
   ① Lack of one phase of power supply, or one opposite connection of the stator winding.
   ② Stator winding phase short circuit.
   ③Earthing of the stator winding
   ④ wrong wiring of the stator winding
   ⑤ Fuse section too small.
   ⑥Power line short circuit or grounding.
2. Troubleshooting
   ①Check whether the knife gate has a phase not closed, can power circuit has a phase disconnection; eliminate the reverse connection fault.
   ② find out the short circuit point, be repaired.
   ③ Eliminate grounding.
   ④find out the misconnection, to be corrected.
   ⑤ replace the fuse.
   ⑥ Eliminate the grounding point.

Motor does not rotate with humming sound after power on

1.Cause of fault
(1) The stator and rotor windings have a broken circuit (one phase is disconnected) or one phase of the power supply has lost power.
②The beginning and end of the winding lead wire is connected wrongly or the internal winding is connected backwards.
③ Loose contact point of power circuit, large contact resistance.
④The motor load is too large or the rotor is stuck.
⑤ The power supply voltage is too low.
(6) Small motor assembly is too tight or the grease in the bearing is too hard.
(7) The bearing is stuck.

2. Troubleshooting
   ①Find out the broken point and repair it.
   ②Check the polarity of the winding; judge whether the end of the winding is correct.
   ③Tighten the loose wiring screws and use a multimeter to determine whether the joints are falsely connected and repair them.
   ④ Reduce the load or find out and eliminate mechanical faults.
   ⑤ check whether the specified Δ connection is also mistakenly connected to Y; whether the voltage drop is too large because the power supply wire is too thin, to be corrected.
   ⑥reassemble to make it flexible; replace qualified grease.
   ⑦ Repair the bearings.

Motor no-load current imbalance, three big difference

1. Cause of failure
   ① rewinding, stator three phase winding turns are not equal.
   ② wrong winding first and last end connection.
   (iii) unbalanced power supply voltage.
   ④There is a short circuit between the turns of the winding, coil reversal and other faults.
2. Troubleshooting
   ① re-wind the sub-winding.
   ②Check and correct.
   ③ Measure the power supply voltage and try to eliminate the imbalance.
   ④Clear the winding fault.

Motor no load, overload, the ammeter pointer is unstable, swing

1. Cause of fault
   ①Cage rotor guide bar open weld or broken bar.
   ② winding rotor fault (a phase break) or brush, collector ring short-circuit device poor contact.
2. Troubleshooting
   ① find out the broken strip to repair or replace the rotor.
   ② Check the rotor winding circuit and repair it.

Motor no-load current balance, but the value is large

1．Cause of failure
①repair, stator winding turns reduce too much.
②The power supply voltage is too high.
③Misconnection of Y-connected motor as Δ.
④In motor assembly, the rotor is installed backwards, so that the stator core is not aligned and the effective length is shortened.
⑤ too large or uneven air gap.
(6) When dismantling the old winding during overhaul, the core is burnt by using improper hot dismantling method.

2. Troubleshooting
   ① re-winding the stator winding, restore the correct number of turns.
   ② try to restore the rated voltage.
   ③ rewire to Y.
   ④ Reassemble.
   ⑤ Replace the rotor with a new one or adjust the air gap.
   (6) Overhaul the iron core or recalculate the winding to increase the number of turns appropriately.

Motor start difficulty, rated load, speed is more than the rated speed

1. Cause of failure
   ①The power supply voltage is too low.
   ②Misconnection of Δ-connector motor to Y.
   ③Cage rotor open welding or fracture
   ④Stator and rotor local coil misconnection or reverse connection.
   ⑤ repairing the motor winding to increase the number of turns too much.
   ⑥Motor overload.
2. Troubleshooting
   ① Measure the power supply voltage and try to improve it.
   ② Correct the connection method.
   ③Check the open and broken weld and repair.
   ④Find out the misconnection and correct it.
   ⑤ Restore the correct number of turns.
   (6) Reduce the load.

Motor overheating or even smoke

1. Cause of failure
   ① The power supply voltage is too high, which makes the iron core heat up greatly.
   ②The power supply voltage is too low, and the motor is running with rated load, the current is too big for the winding to heat up.
   ③When repairing and dismantling the winding, the hot dismantling method is not appropriate, which burns the iron core.
   ④The stator and rotor iron cores rub each other.
   ⑤ motor overload or frequent starting.
   ⑥Breakage of the cage rotor.
   (7) Motor is out of phase, two-phase operation.
   (8) Insufficient dipping paint on the winding after rewinding.
   ⑨High ambient temperature and dirt on the surface of the motor, or blocked ventilation channels.
   ⑩Motor fan failure, poor ventilation; stator winding fault (phase to phase, turn to turn short circuit; stator winding internal connection error).
2. Troubleshooting
   ① lower the power supply voltage (such as adjusting the power supply transformer tap), if the motor Y, Δ connection error caused by, then should correct the connection.
   ② Raise the power supply voltage or change the thick supply wire.
   ③ overhaul the iron core to remove the fault.
   ④ Eliminate the friction point (adjust the air gap or frustration, turn the rotor).
   ⑤ Reduce the load; control the start according to the number of times specified.
   ⑥Check and eliminate rotor winding faults.
   (vii) restoration of three-phase operation.
   ⑧ Adopt secondary dipping paint and vacuum dipping paint process.
   ⑨ Clean the motor, improve the ambient temperature and adopt cooling measures.
   ⑩Check and repair the fan, replace it if necessary; overhaul the stator winding to eliminate the fault.

Motor bearing overheating

1.Cause of failure
① Too much or too little grease.
② bad oil quality containing impurities.
③ bearing and journal or end cover with improper fit (too loose or too tight)
④The bearing bore is eccentric and rubs against the shaft.
⑤ the motor end cover or bearing cover is not installed flat.
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.
(8) The motor shaft is bent.

2. Troubleshooting
   ①Add grease according to regulations (1/3-2/3 of the volume).
   ②Replace clean lubricating grease.
   ③ too loose available binder repair, too tight should be car, grinding journal or end cover bore, make it suitable.
   ④Repair the bearing cover to eliminate the rubbing point.
   ⑤ Reassembly.
   (6) recalibrate and adjust the belt tension.
   ⑦Replacement of new bearings.
   ⑧ Correct the motor shaft or replace the rotor.

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