Oil and Vibration Analysis
Team Up to Save Electric Motor Bearings
This case study demonstrates how oil analysis and vibration
analysis worked together to effectively increase the availability and reliability
of a 300-horsepower vertical motor. The motor is used to pump sea water
into a condenser that condenses steam after use in a turbine. Oil analysis
found
that the
oil lubricating the motor's thrust bearing was contaminated with water,
and vibration analysis confirmed the bearing’s condition and elevated the
criticality of the alarm.
Vibration readings are taken on this equipment monthly. During
April and May vibration readings fluctuated above alert levels, but did
not indicate an immediate need for repair.
On May 30, oil analysis revealed that the upper bearing of
the motor contained a large amount of water (see
5/30 column of oil analysis report).
A work request was made to change the oil at the next opportune
time, and investigate the source of water ingress. A vibration reading
was taken during this time to ensure the vibration
trend was stable.
Over the next two months, vibration amplitudes increased
over fault levels, and the oil change out was placed at a higher priority.
At this time, we were confident that the water ingress was hindering the
lubrication of the bearing, causing the elevated vibration levels. The
oil was replaced on July 17, and subsequent vibration amplitudes decreased
dramatically and remained below alert levels.
There may have been a time when advanced technologies competed
with one another. However, in today’s work environment, it is vital that
technologies complement rather than compete. If only vibration technology
was used, this motor would have been subjected to higher vibration amplitudes,
and the work request would have been made to inspect the bearing and equipment.
However, upon inspection, the tradesmen would have found very little evidence
of a bearing problem because the bearing fault was still in incipient stages.
It may also be possible that the water in the oil may not
have been noticed and oil not replaced if the inspection was done by lifting
the top cover. At the end of the job, the motor quite possibly could have
been placed back into service only to find vibration levels continuing
to be high. Coupled with oil analysis, the equipment was fixed and correctly
put back into service.
Submitted by Cyril Ontai, Hawaiian
Electric Company, Inc.
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