Thirteen Q&A questions about Hengli Motors

1. Why does the motor generate shaft current?

The current in the motor shaft bearing seat base circuit is called shaft current. Reasons for shaft current generation:

(1) Magnetic field asymmetry; (2) There are harmonics in the power supply current; (3) Poor manufacturing and installation, resulting in uneven air gap due to rotor eccentricity; (4) There is a gap between the two semicircles of the detachable stator core; (5) The number of splices for stator cores with fan-shaped stacking is not appropriate.

Harm: Corrosion of the surface of motor bearings or ball bearings, formation of point like micro holes, deterioration of bearing performance, increased friction loss and heat generation, ultimately leading to bearing burnout.

Prevention: (1) Eliminate pulsating magnetic flux and power harmonics (such as installing AC reactors on the output side of the frequency converter); (2) When designing the motor, the bearing seat and base of the sliding bearing should be insulated, and the outer ring and end cover edge of the rolling bearing should be insulated.

2. Why can't general motors be used in high-altitude 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, and the lower the output power. But when the temperature decreases with the increase of altitude enough to compensate for the impact of altitude on temperature rise, the rated output power of the motor can remain unchanged; (2) When high-voltage motors are used on high altitudes, anti corona measures should be taken; (3) Altitude is not conducive to the commutation of DC motors, 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 operates under light load, it will cause:

(1) Low motor power factor; (2) The motor efficiency is low. It will cause equipment waste and uneconomical operation.

4. What are the reasons for motor overheating?

(1) Excessive load; (2) Lack of phase; (3) Air duct blockage; (4) Long low-speed operation time; (5) The power harmonic is too large.

5. What work needs to be done before putting a motor that has been unused for a long time into use?

(1) Measure the insulation resistance between stator and winding phases, as well as between windings and ground. The insulation resistance R should satisfy the following equation:

R> Un/(1000+P/1000) (M Ω) Un: Rated voltage of motor winding (V) P: Motor power (KW)

For motors with Un=380V, R>0.38M Ω.

If the insulation resistance is low, it can be: a： Motor runs without load for 2-3 hours for drying; b： Use 10% rated voltage low-voltage AC power to enter the winding or connect the three-phase winding in series and use DC electric drying to maintain the current at 50% of the rated current; c： Use a fan to send hot air or heating elements for heating. (2) Clean the motor; (3) Replace the bearing grease.

6. Why can't motors be started arbitrarily in cold environments?

If the motor is left in a low-temperature environment for too long, it will: (1) cause insulation cracking of the motor; (2) Freezing of bearing grease; (3) Solder powdering of wire joints. Therefore, the motor should be heated and stored in cold environments, and the windings and bearings should be inspected before operation.

7. What are the reasons for unbalanced three-phase current in motors?

(1) Three phase voltage imbalance; (2) Poor welding or poor contact of a certain phase branch inside the motor; (3) Motor winding inter turn short circuit or ground or phase to phase short circuit; (4) Wiring error.

8. Why can't a 60Hz motor be connected to a 50Hz power supply?

When designing motors, silicon steel sheets are generally operated in the saturation zone of the magnetization curve. When the power supply voltage is constant, reducing the frequency will increase the magnetic flux and excitation current, resulting in an increase in motor current and copper consumption, ultimately leading to an increase in motor temperature rise. In severe cases, the motor may also be burned due to overheating of the coil.

9. What are the reasons for motor phase loss?

In terms of power supply: (1) Poor contact of the switch; (2) Transformer or line disconnection; (3) Insurance circuit breaker.

In terms of motors: (1) Loose screws and poor contact in the motor junction box; (2) Poor welding of internal wiring; (3) The motor winding is broken.

10. What are the reasons for abnormal vibration and sound of the motor?

Mechanical aspect: (1) Poor bearing lubrication and bearing wear; (2) Loose fastening screws; (3) There are debris inside the motor.

Electromagnetic aspect: (1) Motor overload operation; (2) Three phase current imbalance; (3) Lack of phase; (4) Short circuit fault in stator and rotor windings; (5) The welding part of the cage rotor broke due to welding.

11. What work needs to be done before starting the motor?

(1) Measure insulation resistance (not less than 0.5M Ω for low voltage motors); (2) Measure the power supply voltage. Check if the motor wiring is correct and if the power supply voltage meets the requirements; (3) Check if the starting equipment is in good condition; (4) Check if the fuse is suitable; (5) Check whether the motor grounding and neutral connection are good; (6) Check if there are any defects in the transmission device; (7) Check if the motor environment is suitable and remove flammable materials and other debris.

12. What are the reasons for overheating of motor bearings?

The motor itself: (1) The inner and outer rings of the bearing are too tightly matched; (2) There are problems with the shape and position tolerances of components, such as poor coaxiality of machine bases, end caps, shafts, and other parts; (3) Improper selection of bearings; (4) Poor lubrication of bearings or incomplete cleaning of bearings, with impurities in the lubricating grease; (5) Axis current.

In terms of use: (1) Improper installation of the unit, such as the coaxiality of the motor shaft and the dragged device shaft meeting the requirements; (2) Pulling the pulley too tightly; (3) Poor maintenance of bearings, insufficient or expired lubricating grease, and deterioration due to dryness.

13. What are the reasons for low insulation resistance of motors?

(1) The winding is damp or has water ingress; (2) Accumulation of dust or oil on the winding; (3) Insulation aging; (4) The insulation of the motor lead or terminal block is damaged.