Bearing lubrication assessment using an statistical analysis of the stator current spectrum

Bearing lubrication is very important to ensure a satisfactory and long operation of bearings. An excess of lubrication can be as damaging as a lack of lubrication. An excess of oil or grease has damaging effects in the short term such as difficult heat evacuation, sliding balls and greater current consumption. There are some procedures, such as acoustic monitoring and methods based in charts provided by manufacturers, to decide when to regrease a bearing and how much grease is needed. As Motor Current Signature Analysis is widely recognized as a useful and reliable tool for condition monitoring of induction motors, it has been used, along with an Analysis of Covariance, to find signs in the stator current spectrum of an excess of lubrication. The statistical analysis shows that the variation observed in some integer harmonics of the supply frequency is due to different levels of bearing lubrication.