1. Why does the motor produce axial current?
The current in the circuit of the shaft - bearing - base of the motor is called shaft current. The causes of axial current are as follows: (1) magnetic field asymmetry; (2) there are harmonics in the power supply current; (3) the manufacture and installation are not good, and the air gap is uneven due to the rotor eccentricity; (4) there are gaps between the two semicircles of the detachable stator core; (5) The number of pieces of stator cores with fan-shaped laminated cores is not appropriate. Harm: make the motor bearing surface or ball erosion, shape of the point micro hole, make the bearing performance deterioration, friction loss and heat increase, eventually cause bearing burning. Prevention: (1) eliminate pulsating flux and power harmonics (such as installing AC reactor on the output side of the frequency converter); (2) when the motor is designed, the bearing seat and base of the sliding bearing are insulated, and the outer ring and end cover of the rolling bearing are insulated.

2. Why can't the general motor be used in the plateau area?
Elevation has adverse effects on motor temperature rise, motor corona (high voltage motor) and DC motor reversing. Attention should be paid to the following three aspects: (1) the higher the altitude, the greater the motor temperature rise, the smaller the output power. However, when the temperature decreases with the increase of altitude enough to compensate for the influence of altitude on the temperature rise, the rated output power of the motor can remain unchanged. (2) Corona prevention measures should be taken when high voltage motor is used at high altitude; (3) The altitude is unfavorable to the DC motor commutation, so we should pay attention to the selection of carbon brush materials.

3. Why should the motor not run under light load?
When the motor is carried lightly, it will cause: (1) the low power factor of the motor; (2) Low motor efficiency. It will cause waste of equipment and uneconomical operation.

4. What are the reasons for the motor overheating?
(1) excessive load; (2) phase loss; (3) air duct blockage; (4) Low speed running time is too long; (5) Power harmonic is too large.

5. What work should be done before putting the unused motor into use?
(1) Measure the insulation resistance of each phase of stator and winding to the ground. Insulation resistance R should meet the following formula: R > UN /(1000+P/1000)(MΩ) UN: motor winding rated voltage (V) P: motor power (KW) For Un = 380V motor, R > 0.38M nm. If the insulation resistance is low, it can be: A: the motor runs 2 ~ 3h drying without load; B: Use the low-voltage alternating current of 10% rated voltage to enter the windings or connect the three-phase windings in series with direct current drying to keep the current at 50% rated current; C: Use fan to feed hot air or heating element for heating. (2) Clean the motor. (3) replace the bearing grease.

6, why can not arbitrarily start the motor in the cold environment?
If the motor is too long in low temperature environment, it will: (1) Motor insulation cracking; (2) bearing grease freezing; (3) wire joint soldering powder. Therefore, the motor should be heated and stored in the cold environment, and the windings and bearings should be checked before operation.

7. What are the reasons for the three-phase current imbalance of the motor?
(1) Unbalance of three-phase voltage; (2) The welding or contact of a phase branch inside the motor is bad; (3) short circuit between turns of motor winding or short circuit to ground and phase; (4) Wiring error.

8. Why can't a 60Hz motor be connected to a 50Hz power supply?
When the motor is designed, the silicon steel sheet generally works in the saturation zone of the magnetization curve. When the power supply voltage is constant, the reduced frequency will increase the magnetic flux, increase the excitation current, lead to the increase of the motor current, increase the copper consumption, and eventually lead to the increase of the motor temperature. In serious cases, the motor may be burned down due to overheating of the coil.

9. What are the reasons for phase loss of the motor?
Power supply: (1) poor switch contact; (2) Disconnection of transformer or line; (3) Insurance fuse. Motor: (1) screw loose of motor junction box and poor contact; (2) Bad welding of internal wiring; (3) The motor winding is broken.

10. What are the causes of abnormal vibration and sound of the motor?
Mechanical aspects: (1) poor bearing lubrication, bearing wear; (2) loose fastening screw; (3) There are sundries in the motor. Electromagnetic aspects: (1) motor overload operation; (2) Unbalance of three-phase current; (3) phase loss; (4) short circuit fault of stator and rotor windings; (5) the welding part of the cage rotor is broken by open welding.

11. What work should be done before starting the motor?
(1) measurement of insulation resistance (for low voltage motor should not be less than 0.5m Ω); (2) Measure the power supply voltage. Check whether the motor wiring is correct and whether the power supply voltage meets the requirements; (3) check whether the starting equipment is in good condition; (4) check whether the fuse is suitable; (5) Check whether the motor is grounded and zero connected; (6) Check whether there are defects in the transmission device; (7) Check whether the motor environment is appropriate and remove flammable goods and other sundries.

12. What are the causes of overheating of motor bearings?
Motor itself: (1) The inner and outer rings of the bearing are too tight; (2) There are problems with the shape and position tolerance of parts, such as poor coaxiality of machine base, end cover, shaft and other parts; (3) improper selection of bearings; (4) poor bearing lubrication or bearing cleaning is not clean, there are sundries in the grease; (5) Axial current. Usage: (1) improper installation of the unit, such as the motor shaft and the shaft of the dragging device coaxiality of a requirement; (2) pulley pulling too tight; (3) the bearing is not maintained well, the grease is insufficient or exceeds the service life, and the hair is dry and bad.

13. What are the reasons for the low insulation resistance of the motor?
(1) The winding is damp or water invades; (2) Dust or oil accumulates on the winding; (3) insulation aging; (4) Motor lead wire or terminal board insulation damage.