Once a permanent magnet motor loses its magnetism, the only option is to replace the motor , which is very costly. So how do you determine if a permanent magnet motor has lost its magnetism? Let's continue reading.
The machine's current is normal at startup, but increases after a period of time, eventually triggering an inverter overload warning. First, confirm that the air compressor manufacturer has selected the correct inverter, and then check if the inverter's parameters have been altered. If both are fine, then the back electromotive force (EMF) needs to be checked. Disconnect the compressor head from the motor and perform a no-load test. Run the compressor at its rated frequency; the output voltage at this point is the back EMF. If it is more than 50V lower than the back EMF on the motor's nameplate, the motor is demagnetized.
Overload operation of permanent magnet motors is mainly caused by excessive load, low voltage, or mechanical jamming. If the overload lasts for too long, the permanent magnet motor will absorb a large amount of active power from the power grid, increasing the current and temperature. At high temperatures, the insulation of the permanent magnet motor will age, and the magnets will lose magnetism. Therefore, during operation, it is important to regularly check whether the transmission device operates flexibly and reliably; whether the concentricity of the coupling is standard; and the flexibility of the gear transmission. If jamming is found, the motor should be stopped immediately to investigate the cause and troubleshoot before restarting.
For a three-phase AC permanent magnet motor, the difference between the average current of any one phase and the average current of the other two phases must not exceed 10% to ensure the safe operation of the permanent magnet motor. If the difference exceeds 10%, it indicates that the permanent magnet motor is faulty and must be investigated.
Check if the permanent magnet motor bearing is overheating or lacking lubrication. If excessive temperature rise is found near the bearing, stop the machine immediately for inspection. Check for cracks, scratches, or defects on the rolling elements and raceway surfaces of the bearing, excessive bearing clearance, and whether the inner ring rotates on the shaft. If any of these phenomena occur, the bearing must be replaced before resuming operation.
If a permanent magnet motor vibrates, it can cause misalignment of the connected load components, increasing the motor's load and leading to overload operation, which can burn out the motor. Therefore, during operation, especially for high-power permanent magnet motors, it is essential to frequently check whether the foundation bolts, end covers, bearing caps, etc., are loose, and whether the grounding device is reliable. Any problems should be addressed promptly.
During operation, the area within at least 3 meters of the air intake of a permanent magnet motor must be free of dust, water stains, and other debris to prevent them from being drawn into the motor, forming a short-circuit medium, or damaging the wire insulation, causing a short circuit and burning out the motor. Therefore, it is necessary to ensure that the permanent magnet motor has sufficient insulation resistance and a good ventilation and cooling environment to maintain a safe and stable working state during long-term operation.
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