August 2010

Special Report: Fluid Flow and Rotating Equipment

Prevent electric erosion in variable-frequency drive bearings

Here are the reasons and remedial actions

Bloch, Heinz P., Hydrocarbon Processing Staff

The problem of electric current passing through electrical machine rolling bearings and causing damage in the inner and outer ring ball or roller and raceway contact areas has been known for decades. In addition to the bearing element damage, it was also understood that the lubricant structure might change under the influence of a passing current. Both AC and DC motors potentially suffer from the electric-current passage phenomenon. However, since the 1990s, increasing use of variable-frequency drives (VFDs) has had a measurable effect on the number of motor bearing failures. This article examines the reasons and recommends remedial action to be considered. Modern induction machines are con

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