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 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 a 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 eight-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.