inverter and the motor

Damage to the motor caused by the inverter includes two aspects: stator winding damage and bearing damage. This damage usually occurs within a few weeks to ten months. The specific time depends on the inverter brand, motor brand, motor power, and inverter carrier frequency. , the length of the cable between the inverter and the motor, the ambient temperature and other factors. The mechanism of motor bearing damage caused by frequency converter: The reason why the frequency converter damages the motor bearings is that there is current flowing through the bearings, and this current is in a state of intermittent communication. The intermittent communication circuit will generate arcs and burn the bearings. There are two main reasons for current flow in AC motor bearings: one is the induced voltage caused by the imbalance of the internal electromagnetic field; the other is the high-frequency current path caused by stray capacitance. When the currents of the three-phase windings are equal and the phase difference is 120°, the magnetic field inside the ideal AC induction motor is symmetrical? No voltage will be induced on the motor shaft. When the PWM voltage output by the inverter causes the internal magnetic field of the motor to be asymmetrical, A voltage will be induced on the shaft, with an amplitude between 10-30v, related to the driving voltage. The higher the drive voltage, the higher the voltage on the shaft. When this voltage value exceeds the dielectric strength of the lubricating oil in the bearing, a current path will be formed. During the rotation of the shaft, at a certain moment, the insulation of the lubricating oil blocks the current again. This process is similar to the on-off process of a mechanical switch. During the on-off process, an arc will be generated, and the arc will ablate the shaft, ball and The surface of the shaft bowl forms pits. If there is no external vibration, the small pits will not have much impact, but if there is external vibration, grooves will be formed, which will have a great impact on the operation of the motor. In addition, experiments show that the voltage on the shaft is also related to the fundamental frequency of the inverter output voltage. The lower the fundamental frequency, the higher the voltage on the shaft, and the more serious the bearing damage will be. In the early stages of motor operation, when the lubricating oil temperature is low, the current amplitude is 5-200 mA. Such a small current will not cause any damage to the bearings. However, after the motor has been running for a period of time, as the lubricating oil temperature increases, The peak current will reach 5-10A, which will cause arcing and form small pits on the surface of bearing parts. If you want to know more about the problem of motor bearing damage caused by frequency converters, please continue to pay attention to the updated information of our website.!sales@schwahrtechnology.com