Bearing problem solved
May 1st 2007

AV Technology has used its expertise in Root Cause Analysis (RCA) to identify the reasons for a recurring bearing problem on a large electric motor operating at Solvay Interox, Warrington.

The 350kW variable speed, inverter-driven motor drives a screw compressor providing process air for the hydrogen peroxide plant.

Failure of the motor would result in significant reduction in throughput. AVT was awarded a condition monitoring contract for the site and identified a bearing problem on the motor. A bearing change was scheduled and the damaged bearing returned to AVT for RCA.

Inspection of the bearing revealed fluting on the outer race and darkening of the balls, a sign that electric current was passing through during operation.

A call to the motor maker revealed that the bearing should have been insulated to prevent shaft voltages causing circulating currents to pass through bearing and frame.

AVT believes the original insulated bearing was replaced by a repairer for a non-insulated type which, in turn, was replaced by another un-insulated bearing, and the mistake perpetuated.

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