Cause Analysis of AC Servo Motor Damage

Three phase AC servo motors are widely used, but after a long period of operation, various faults will occur. It is an important work to determine the cause of the fault in time and deal with it accordingly to prevent the fault from expanding and ensure the normal operation of the equipment.

1、 After power on, the motor cannot rotate, but there is no abnormal noise, odor and smoke.

1. Fault cause ① Power supply is not connected (at least two phases are not connected); ② Fuse fusing (at least two phase fusing); ③ The over-current relay is too small; ④ The control equipment is wired incorrectly.

2. Troubleshooting ① Check the power circuit switch, fuse and junction box for breakpoints and repair them; ② Check the fuse model, cause of fusing and replace it with a new one; ③ Adjust the relay setting value to match with the motor; ④ Correct the wiring.

2、 The motor does not rotate and hums after power on

1. Cause of fault: ① The rotor winding has open circuit (one phase is broken) or one phase of the power supply loses power; ② The beginning and end of the winding outgoing line are wrongly connected or the winding is reversely connected internally; ③ The contact of power circuit is loose and the contact resistance is large; ④ The motor is overloaded or the rotor is stuck; ⑤ The power supply voltage is too low; ⑥ Small motors are assembled too tightly or grease in bearings is too hard; ⑦ The bearing is stuck.

2. Troubleshooting ① Identify the fault point and repair it; ② Check the winding polarity; Judge whether the winding end is correct; ③ Fasten the loose wiring screws, use a multimeter to judge whether each connector is falsely connected, and repair it; ④ Reduce the load or find out and eliminate the mechanical fault, ⑤ check whether the specified surface connection method is wrongly connected; If the voltage drop is too large due to too thin power supply wire, correct it. ⑥ Reassemble it flexibly; Replace qualified grease; ⑦ Repair the bearing.

3、 It is difficult to start the motor, and the motor speed is much lower than the rated speed under the rated load

1. Fault cause ① The power supply voltage is too low; ② The motor of surface connection method is wrongly connected; ③ The rotor is cracked or broken; ④ The local coils of the rotor are wrongly connected or inversely connected; ③ Too many turns are added when repairing the motor winding; ⑤ Motor overload.

2. Troubleshooting ① Measure the power supply voltage and try to improve it; ② Correct connection; ③ Check the open weld and broken point and repair them; ④ Find out the wrong connection and correct it; ⑤ Restore the correct number of turns; ⑥ Load shedding.

4、 The motor no-load current is unbalanced, and the three-phase difference is large

1. Cause of fault ① Wrong connection of winding head and tail; ② The power supply voltage is unbalanced; ③ The winding has inter turn short circuit, coil reverse connection and other faults.

2. Troubleshooting ① Check and correct; ② Measure the power supply voltage and try to eliminate the imbalance; ③ Eliminate winding faults.

5、 The motor makes abnormal noise during operation

Cause of failure: ① The bearing is worn or there are sand particles and other foreign matters in the oil; ② Loose rotor core; ③ The bearing is short of oil; ④ The supply voltage is too high or unbalanced.

Troubleshooting ① Replace or clean the bearing; ② Overhaul the rotor core; ③ Refueling; ④ Check and adjust the power supply voltage.

6、 The motor vibrates greatly during operation

Cause of failure: ① The clearance of worn bearing is too large; ② Uneven air gap; ③ Rotor unbalance; ④ Bent shaft; ⑤ Coaxiality of coupling (pulley) is too low.

Troubleshooting ① Repair the bearing and replace it if necessary; ② Adjust the air gap to make it uniform; ③ Correct rotor dynamic balance; ④ Straighten the shaft; ⑤ Recalibrate to make it meet the requirements.

7、 Bearing overheating

1. Fault cause ① Too much or too little grease; ② Poor oil quality contains impurities; ③ Improper matching of bearing and journal or end cover (too loose or tight); ④ The bearing bore is eccentric and rubs against the shaft; ⑤ Motor end cover or bearing cover is not installed flat; ⑥ The coupling between the motor and the load is not corrected, 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 lubricating grease (1/3-2/3 of the volume) as required; ② Replace the clean lubricating grease; ③ If it is too loose, it can be repaired with adhesive. If it is too tight, it should be turned. Grind the inner hole of journal or end cover to make it suitable; ④ Repair the bearing cover and eliminate the friction points; ⑤ Reassemble; ⑥ Recalibrate and adjust the belt tension; ⑦ Replace with a new bearing; ⑧ Correct the motor shaft or replace the rotor.

8、 The motor is overheated and even smokes

Fault causes: ① The power supply voltage is too high; ② If the power supply voltage is too low, the motor will run with rated load, and excessive current will cause winding heating; ③ When repairing and removing the winding, the hot removal method is improper, which burns the iron core; ④ Motor overload or frequent starting; ⑤ Motor phase loss, two-phase operation; ⑥ After rewinding, the winding is not fully dipped in paint; ⑦ There is much dirt on the surface of the motor when the ambient temperature is high, or the ventilation duct is blocked;

Troubleshooting ① Reduce the power supply voltage (such as adjusting the tap of the power supply transformer); ② Increase the power supply voltage or replace the thick power supply wire; ③ Repair the iron core and remove the fault; ④ Load reduction; Control the starting according to the specified times; ⑤ Restore three-phase operation; ⑥ The secondary impregnation and vacuum impregnation processes are adopted; ⑦ Clean the motor, improve the ambient temperature and take cooling measures;