Effects of electrostatic discharges on bearing grease electric properties

Bearing faults may significantly reduce the useful life of electric machines. With the advent of modern fast-switching frequency converters, electric currents induced by the high-frequency common-mode voltage of these converters have been recognized as additional, sometimes severe, contributors to bearing degradation. The degradation is understood to progress both by damaging bearing surfaces and by altering the chemical composition of lubrication greases, which can lead to ineffective lubrication and reduction in permissible mechanical bearing load. This paper studies the effect of grease degradation due to discharge currents on the grease electric properties of several greases typically used with electric drives.