Motor repair and maintenance

1, why the motor shaft current? Motor shaft --- bearing --- base loop current is called the shaft current. (1) Magnetic field asymmetry; (2) Harmonic in supply current; (3) Manufacturing and installation is not good due to rotor eccentricity resulting in uneven air gap; (4) Detachable stator core two A gap between the semicircles; (5) fan-shaped stacked stator core number of pieces selected inappropriate. Hazard: The motor bearing surface or ball erosion, punctured micropore form, so that deterioration of bearing performance, friction loss and heat increase, eventually causing the bearing burned. Prevention: (1) Elimination of pulsating magnetic flux and power harmonics (such as installing AC reactor on the output side of the inverter); (2) Insulating the bearing seat and the base of the plain bearing when the motor is designed; Cover insulation. 2, why the general motor can not be used in the plateau area? Altitude of the motor temperature rise, the motor corona (high voltage motor) and the DC motor has adverse effects. Should pay attention to the following three aspects: (1) high altitude, the greater the motor temperature rise, the smaller the output power. However, the rated output power of the motor may not change when the temperature decreases with the altitude increasing enough to compensate for the elevation effect on the temperature rise. (2) The high-voltage motor should be protected against corona when it is used on the plateau. (3) The altitude Reversal of the DC motor adverse, we should pay attention to the choice of carbon brush material. 3, the motor should not be light-load operation? When the motor is running lightly, it will cause: (1) Low motor power factor; (2) Low motor efficiency. Will result in waste of equipment, operating uneconomical. 4, the motor overheating what are the reasons? (1) load is too large; (2) lack of phase; (3) duct blockage; (4) low speed running time is too long; 5, a long set aside before the need to do what the motor input? (1) measuring stator, winding phase and winding insulation resistance. Insulation resistance R should satisfy the following formula: R> Un / (1000 + P / 1000) (MΩ) Un: Motor winding voltage rating (V) P: Motor power (KW) R> 0.38MΩ for Un = 380V motor. If the insulation resistance is low, it can be: a: the motor runs in no-load running for 2 ~ 3h; b: the low-voltage alternating current of 10% of the rated voltage is applied to the winding or the three- Rated current; c: with the fan into the hot air or heating element heating. (2) clean the motor. (3) replace the bearing grease. 6, why can not start the motor in cold environment? Motor in the low temperature environment is too long, will: (1) motor insulation cracking; (2) bearing grease freeze; (3) conductor solder powder. Therefore, the motor should be heated in a cold environment, the winding and bearing should be checked before operation. 7, the three-phase motor current imbalance What are the reasons? (1) Unbalanced three-phase voltage; (2) Poor welding or poor contact of one phase of the internal motor; (3) Turn-to-turn short circuit between the windings of the motor or to ground and short circuit; (4) Wrong connection. Why 60Hz motor can not be connected to 50Hz power supply? When designing the motor, the silicon steel sheet generally works in the saturation region of the magnetization curve. When the power supply voltage is constant, decreasing the frequency increases the magnetic flux and the excitation current increases, resulting in an increase of the motor current and an increase of the copper loss, which eventually leads to an increase of the motor temperature rise. In severe cases, the motor may also be burned due to overheating of the coil. 9, the motor phase loss what are the reasons? Power: (1) poor switch contact; (2) transformer or line break; (3) fuse fuse. Motor: (1) motor junction box screw loose loose contact; (2) poor internal wiring welding; (3) motor winding disconnected. 10, caused by abnormal motor vibration and sound what are the reasons? Mechanical aspects: (1) poor bearing lubrication, bearing wear and tear; (2) fastening screws loose; (3) motor debris. Electromagnetic: (1) motor overload operation; (2) three-phase current imbalance; (3) lack of phase; (4) stator and rotor winding short circuit fault; 11, before starting the motor what needs to be done? (1) Insulation resistance measurement (low voltage motor should not be less than 0.5MΩ); (2) measure the supply voltage. Check the motor wiring is correct, the supply voltage meets the requirements; (3) Check the starting equipment is good; (4) Check the fuse is appropriate; (5) Check the motor ground, pick zero is good; Defects; (7) Check the motor environment is appropriate to remove flammable materials and other debris. 12, the motor bearing overheating what are the reasons? The motor itself: (1) the bearing inner and outer ring with too tight; (2) parts of the form of tolerances, such as the seat, cover, shaft and other parts of poor coaxiality; (3) Bearing lubrication or bearing cleaning is not clean, there are debris in the grease; (5) shaft current. The use of: (1) improper installation of the unit, such as the motor shaft and the device to be driven by a coaxial axis together; (2) pull the pulley tight; (3) bearing maintenance is not good, grease is insufficient or more than the use of Period, hair dry metamorphism. 13, low motor insulation resistance what are the reasons? (1) the winding damp or water invaded; (2) the accumulation of dust or oil on the winding; (3) insulation aging; (4) Motor Lead or Procurement pump accessories [] ball valve [purchase] submersible pump [purchase] U Humidifier [Buy] Pumps [Procurement] Safety valve combinations [Procurement] Mary Steel Pipe fittings [Procurement] Industrial Pumps [Procurement] Pumps