AC motor common problem summary


No matter what products will have some common problems, […]

No matter what products will have some common problems, AC motor is no exception, the following Junneng motor editor will introduce the common problems of AC motor.

  1. Why does the motor generate shaft current?

The current in the shaft-bearing seat-base loop of the motor is called shaft current.

The causes of axial current are as follows:

(1) asymmetrical magnetic field;

(2) harmonics in power supply current;

(3) poor installation, caused by uneven air gap due to rotor eccentricity;

(4) gap between two semicircles of detachable stator core;

(5) inappropriate selection of pieces with sector stacked stator core.


the surface or the ball of the motor bearing is eroded, the form-path point-like micro-pores are formed, the operation performance of the bearing is deteriorated, the friction loss and the heat generation are increased, and the final result The bearing is burned.


(1) remove pulsating flux and power harmonics (such as adding AC reactor);

(2 to the output side of the converter), insulate the bearing seat and base of the sliding bearing, and insulate the outer ring and end cover of the rolling bearing.

  1. Why can't general motors be used in plateau areas?

Altitude has adverse effects on motor temperature rise, motor corona (high voltage motor) and DC motor commutation. Attention should be paid to the following three aspects:

(1) the higher the altitude, the greater the temperature rise of the motor, the smaller the output power. However, when the temperature decreases with the increase of altitude to compensate for the influence of altitude on the temperature rise, the rated output power of the motor can remain unchanged;

(2) the high voltage motor should take anti-corona measures when it is used at high altitude;

(3) the altitude is disadvantageous to the change of DC motor, so attention should be paid to the selection of carbon brush materials.

     3.why is the motor not suitable for light load operation?

When the motor is in light load operation, it can cause:

(1) The motor power factor is low;

(2) The motor efficiency is low.

It will cause waste of equipment and uneconomical operation.

(1) the load is too large;

(2) the phase is missing;

(3) the air duct is blocked;

(4) the running time is too long at low speed;

(5) the harmonics of the power supply are too large.

    4.why can't you start a motor in a cold environment at will?

If the motor is too long in low temperature environment, it will:

(1) insulation cracking of motor;

(2) freezing of bearing grease;

(3) solder powder of wire joint.

Therefore, the motor should be heated and preserved in cold environment, and the windings and bearings should be checked before operation.

  1. What are the causes of the unbalance of the three-phase current of the motor?

(1) three-phase voltage imbalance;

(2) poor welding or poor contact of a phase branch in the motor;

(3) inter-turn short circuit or ground-to-ground short circuit of the motor winding;

(4) wrong wiring.

6. Why is a 60 Hz motor not connected to a 50 Hz power supply?

When the motor is designed, the silicon steel sheet works in the saturated area of the magnetization curve. When the power supply voltage is fixed, the decrease of frequency will increase the flux and excitation current, which will lead to the increase of motor current and copper consumption, and finally lead to the increase of motor temperature rise. In serious cases, the coil may also burn out the motor because of the overheating of the coil.

  1. What are the reasons for phase loss of the motor?

Power supply:

(1)Poor contact of switch;

(2)Transformer or line disconnection;

 (3)Fuse fuse.


(1) the motor junction box screw loose contact is poor;

(2) the internal wiring welding is poor;

 (3) the motor winding broken wire.

8. What are the causes of abnormal vibration and sound of the motor?

Mechanical aspects:

(1) bearing lubrication is poor, bearing wear;

(2) bearing chamber is too large.

(3) loosening of fastening screw;

(4) sundries in motor.

Electromagnetic aspect:

(1) motor overload operation;

(2) three-phase current imbalance;

(3) lack of phase;

(4) short circuit fault of stator and rotor windings;

(5) opening welding of cage rotor resulting in broken bar.

9. What is the cause of overheating of the motor bearing?

Motor itself:

(1) the inner and outer rings of the bearing are in tight fit;

(2) The dimension tolerance of the parts is a problem, such as the coaxial degree of the parts such as the machine base, the end cover, the shaft and the like is not good;

(3) Improper bearing selection;

(4) The bearing lubrication is poor or the bearing is not clean, and there is sundries in the grease;

(5) Shaft current.

In terms of use:

(1) The unit is not properly installed, such as the shaft of the motor and the shaft of the device to be dragged are not in conformity with the requirements;

(2) the belt pulley is pulled too tightly;

(3) The bearing is not well maintained, the grease is insufficient or the service life is over, and the dry and bad.

10.What are the reasons for the low insulation resistance of the motor?

(1) the winding is wet or water invades;

(2) dust or oil accumulates on the winding;

(3) insulation aging;

(4) insulation damage of motor lead or junction board.

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