Once the permanent magnet motor loses its magnetism, basically we can only choose to replace the motor, and the maintenance cost is a lot of money. How to judge the loss of magnetism of the permanent magnet motor?
The current of the machine is normal when it starts to run. After a period of time, the current becomes larger. After a long time, it will report that the inverter is overloaded. First of all, it is necessary to confirm that the air compressor manufacturer’s frequency converter is correct, and then confirm whether the parameters in the frequency converter have been changed. If there is no problem with both, you need to judge by the back electromotive force, disengage the machine head from the motor, carry out no-load identification, and run it to the rated frequency without load. At this time, the output voltage is the back electromotive force. If it is lower than the motor nameplate If the counter electromotive force is above 50V, it can be determined that the motor is demagnetized.
Therefore, to maintain the normal operation of the permanent magnet motor, the following points need to be paid attention to:
1. Keep the permanent magnet motor working at the rated current
The main reason for the overload operation of the permanent magnet motor is that the dragged load is too large, the voltage is too low, or the driven machinery is stuck. If the overload time is too long, the permanent magnet motor will absorb a large amount of active power from the grid, the current will increase, and the temperature will rise. At high temperatures, the insulation of the permanent magnet motor will age and the magnet will lose its magnetism. Therefore, during the operation of the permanent magnet motor, it is necessary to pay attention to frequently checking whether the transmission device is flexible and reliable; whether the concentricity of the coupling is standard; the flexibility of the gear transmission, etc. If any stagnation is found, it should be stopped immediately to find out the cause and then run after troubleshooting.
2. Frequently check whether the three-phase current of the permanent magnet motor is balanced
For three-phase AC permanent magnet motors, the difference between any one phase current of the three-phase current and the average value of the other two currents is not allowed to exceed 10%, so as to maintain the safe operation of the permanent magnet motor. If it exceeds, it indicates that the permanent magnet motor is faulty and must be checked. bright.
3. Check the temperature of the permanent magnet motor.
Always check whether the temperature of the bearing, stationer, casing and other parts of the permanent magnet motor has abnormal changes. Whether the permanent magnet motor bearing is overheated or lacks oil. If the temperature rises near the bearing too high, stop the machine immediately and check whether there are cracks, scratches or defects on the rolling body and raceway surface of the bearing, and whether the bearing clearance is too large. Whether the inner ring rotates on the shaft, etc. If any of the above phenomena occurs, the bearing must be replaced before it can work again.
4. Observe whether the permanent magnet motor has vibration or loud noise
If the permanent magnet motor vibrates, it will cause the non-concentricity of the load part connected to it, which will increase the load of the permanent magnet motor and cause overload operation, which will burn the motor. Therefore, during the operation of permanent magnet motors, especially high-power permanent magnet motors, it is necessary to frequently check whether the anchor bolts, end covers, bearing glands, etc. are loose, whether the grounding device is reliable, and solve problems in time.
5. Keep the permanent magnet motor clean
During the operation of the permanent magnet motor, dust, water stains and other sundries are not allowed within at least 3m around the air inlet to prevent it from being sucked into the motor, forming a short circuit medium, or damaging the wire insulation, causing a short circuit, and burning the motor. The permanent magnet motor has sufficient insulation resistance and a good ventilation and cooling environment, so that the permanent magnet motor can maintain a safe and stable working state during long-term operation.