Analysis of Bearing Failure and Causes of Shaft Current


According to the bearing failure phenomenon, the main r […]

According to the bearing failure phenomenon, the main reason for the rapid failure of the motor bearing is analyzed, which may be caused by the shaft current. After on-site measurement, it is indeed found that shaft current flows through the bearing.


Judging from the inner sleeve of the free-end bearing that was damaged twice, in addition to the traces of the axial stepped deep groove on the outer ring raceway, there are more point-like micro holes on closer inspection. These dot-shaped micro holes should be caused by shaft current damage to the bearing. The main cause of the shaft current is the large shaft voltage in the motor rotor. Under the action of the shaft voltage, when the motor shaft-bearing seat-base insulation breaks to form a path, the motor generates a very large shaft current. When the current passes through the rotor and the bearing, a discharge phenomenon occurs, causing electric burns to the bearing inner sleeve. Dotted micropores.


As a result, the running performance of the bearing deteriorates, friction loss and heat generation increase, and the bearing temperature rises rapidly, causing the bearing grease to melt and overflow from the bearing. The amount of insulating grease is further reduced, forming a vicious circle, and ultimately leading to rapid bearing damage. Due to the serious wear of the bearing, the motor rotor is displaced, causing the drive end and the non-drive end of the motor rotor to be non-concentric, and the bearing radial force is uneven, causing the bearing outer ring raceway to grind out an axial stepped deep groove similar to a washboard pattern Groove scratches.


Analysis of the reasons for the shaft current generated by the high-voltage motor. There are many reasons for the shaft current generated by the high-voltage motor. One of them is that when the equipment factory manufactures the motor, due to the purity of the raw materials and other objective factors, the stator and rotor of the motor are along the core The magnetic resistance in the circumferential direction is not uniform, and the magnetic flux interlinked with the rotating shaft is generated, thereby inducing the electromotive force. Because the bearings of large motors are not insulated, it is very easy to form shaft current when shaft voltage is generated, and shaft voltage will drop rapidly after shaft current is formed. If the shaft voltage generated by the motor is generally not easy to detect, even if a bearing damage accident occurs, most People can't find the reason for a while. However, when we replace the original bearing with an insulated bearing, we will measure the shaft voltage, and naturally find that the motor has shaft current.


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