Urgent bearing change on 1600 kW motor during crash stop

Three Van Meer service engineers replaced the bearings in a 1,600 kilowatt electric motor at a Dutch waste processing company during a crash stop. The motor was to run for a further ten days up to the planned stop, but action had to be taken sooner to avoid serious damage.

Some six weeks ago our customer observed that one of the motors at the factory was no longer operating as it should. The customer reported this to Van Meer, so we sent a service engineer on site to inspect the motor. Our vibration measurements confirmed the presumption of our customer: starting bearing damage on the non-drive side of the motor.

Damage progression
It was decided in consultation with the technical supervisor to monitor the motor over the coming weeks by including it in a measurement programme to be carried out by Van Meer before the impending stop. The motor was measured and controlled each week to establish the progression of the damage.

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Figure 1 Vibration values per time of measurement

As can be seen on the graphic by the values measured by Van Meer, the vibration values continued to increase (1). In mid-August the motor was again lubricated (2) but this did not help. The negative progression consequently deteriorated further (3).

Crash stop
Because the bearing vibration continued to increase, we advised using the interim crash stop (planned for the next weekend) to preventively replace the bearing. A complete stop was planned at the factory two weeks later, but the engineers from Van Meer could at the time no longer guarantee that the motor would run for a further ten days without further damage being caused.

During the night-time crash stop three engineers proceeded on-site to renew the NAZ bearing in the motor.

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Investigation
The investigation ultimately showed that the bearing was already at damage stage 3 (nearly 4). Should stage four be reached, consequential damage to other components would be unavoidable. This could have caused damage to other bearings or in the worst case the rotor could have fallen through the bearing and caught the stator winding.

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Serious consequential damage could fortunately be prevented thanks to the early observation and the message from the customer, and cooperation with the diagnostic service engineers from Van Meer.

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