Systematic practical approach to the study of bearing damage in a large oil ring lubricated induction machine

The demand for self contained hydrodynamic bearing assemblies has increased in recent years as a result of their lower cost and increased reliability compared to bearings with an external lubrication system. The oil ring lubrication system is the most popular lubricant circulating system used in self contained bearings. Motors with such lubrication system tend to experience bearing damage when the shaft current is sufficiently large. An industry-university research partnership program was instituted to study the shaft current phenomenon in an 8 pole 2611 kW oil ring lubricated sleeve bearing induction machine. The study reviewed all the possible causes of the bearing damage. A series of experimental tests was carried out to determine the cause(s) of the shaft current. These tests included oil analysis, bearing damage analysis and no-load running tests. The tests were conducted using a novel method of shaft current measurement. In addition to the test results, this paper presents a simplified pictorial representation of the significance of joints due to lamination segmentation on the occurrence of shaft current. The paper also includes shaft voltage prediction rules.