There is a high-voltage motor whose bearings at both ends experience significant vibration; the noise produced by these bearings is quite sharp and unpleasant. The vibration level decreased noticeably after applying lubricant!
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The vibration speed measured by the vibration sensor on the front bearing was 8.3 mm/s, with an acceleration of 81 mm/s2; the bearing temperature was 52 degrees. The vibration sensor on the rear bearing indicated a vibration speed of 7.8 mm/s and an acceleration of 92 mm/s2, while the bearing temperature was 65 degrees. The bearings are lubricated with grease! Please advise on the cause of the fault!
This post was last edited by foam_ZPTK on 2018-1-20 at 22:11. It might be caused by shaft current; in large and medium-sized AC motors, once a circuit is formed across the rotor shaft voltage, shaft current is generated. Oil lubrication is used between the shaft and the bearing bush; the motor shaft is pressed against the oil film. Due to the low amplitude of the shaft voltage, the insulation of the oil film generally does not get broken down. During the high-speed operation of the rotor, if the lubricating grease is unsuitable or there is a lack of oil, this can lead to the breakdown of the oil film, resulting in metallic contact between the shaft and the bearing shells. In such cases, a closed circuit is formed by the shaft voltage, leading to low-voltage breakdown. At this time, the shaft current generated is quite large, reaching several hundred amperes or even thousands of amperes in an instant, enough to damage the shaft journals and bearing shells. The static electric charge generated on the shaft due to running friction gradually accumulates, causing the voltage of the shaft to rise continuously as a result of this charging. When the rotating shaft comes into contact with any component other than the rotating body, discharge occurs through that component. When the rotating shaft remains in contact with no components outside the rotating body, charge continues to accumulate, eventually resulting in an excessively high voltage. If this voltage exceeds the insulation strength of the bearing oil film, the charge discharges in an extremely short time, thereby generating an axis current.
It is suspected that a lack of lubricant has caused minor defects (such as chipping or scratches) on the bearing race and either the outer raceway of the bearing (more likely) or the inner raceway (less likely)~~~~~~~ It is recommended to stop the machine at an appropriate time to inspect the bearings~~~
The same goes for rolling bearings; they also need an oil film. Try using an insulated bearing instead
The removed bearing has pits on both the inner and outer rings; please analyze the reason!
Does the area where the shaft current occurs not change color?
Aren’t there damages caused by discharge on the inner and outer rings of the bearing? Take a look at the pictures he uploaded
Is it caused by uneven stress on the outer ring of the bearing due to changes in load? This may also be closely related to the vibrations you experienced earlier