Bearing Fault and Reasons for Axis Current

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      From the inner sleeve of two damaged free end bearings, besides the traces of deep grooves on the outer raceway of axially staircased bearings, there are many dotted micro-holes in the outer raceway. These point-like micro-holes should be caused by the damage of the bearing caused by the shaft current. The main reason for the shaft current is that there is a large shaft voltage in the motor rotor. Under the action of the shaft voltage, when the insulation of the shaft-bearing seat-base of the motor is damaged to form a path, the motor generates a very large shaft current. When the current passes through the rotor and the bearing, the discharging phenomenon occurs, which causes the electric burn of the bearing inner sleeve and produces dotted micro-holes.
Bearing
As a result, the running performance of bearings deteriorates, friction loss and heat increase, and the temperature of bearings rises rapidly, leading to the melting of bearing grease overflow from the bearing, further reducing the amount of insulation grease, forming a vicious circle, and ultimately leading to the rapid damage of bearings. Because of the serious wear of bearings and the displacement of motor rotor, the drive end and non-drive end of motor rotor are not concentric, and the radial force of bearings is not uniform, resulting in the raceway of bearing outer ring grinding out the deep groove scratches similar to the rubbing plate.
There are many reasons for the shaft current produced by high-voltage motor. One of them is that during the manufacture of the motor, due to the restriction of the purity of raw materials and other objective factors, the reluctance of the stator and rotor of the motor is uneven along the circumferential direction of the iron core, which results in the flux linkage with the rotating shaft. The electromotive force is induced. Because the bearings of large motors are not insulated, when the rear pole of the shaft voltage produces, it is easy to form the shaft current, and the shaft voltage after the formation of the shaft current decreases rapidly. If the motor produces the shaft voltage, it is not easy to measure in general, even if the bearing damage accident occurs, most people can not find the reason for the moment. However, when we replace the original bearings with insulated bearings, we will measure the shaft voltage, and naturally find that there is shaft current in the motor.


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