Motor Vibration during solo run

Dear All,

Recently a 550 kw motor bearings were replaced due to an increase in the NDE bearing Peakvue. The vibration was 1.2 mm/s rms.
After overhaul the solo run was taken the vibration increased to 2.8 mm/s rms. This motor bearing was changed for the first time 18 years. It is being felt that the vibrations should be brought back to the previous level.

The dominant frequency in horizontal is 1 X - 2.7 mm/s and a peak at 2 X about 0.2 mm/s.
In the vertical direction - vibration is 1 mm/s

Cross channel phase readings were taken.

NDE H vs V - is 172 Deg
DE H vs V - is 178 deg

NDE Horizontal vs DE Horizontal - is 0 deg (in phase)

Immediate suspicion was soft foot - the same was corrected (0.2 mm was observed in one of the feet was brought down to 0.04 mm) but to avail.

I am not convinced that it could be unbalance based on the phase readings.

The axial vibration levels are 0.74 mm/s
Axial DE left vs right - is 76 deg
Axial top vs bottom - is (-)17 deg

What could be the problem?

Original Post
If this motor is "general purpose", both the vibration values do not sound high.
If the 2.8 mm/sec is collected during the solo run test, I would not balance or do any corrective action before running the motor to its driven machine and take another measurement under normal operating conditions.

I assume it is not a vertical machine since you corrected the foot.

Just curious, as it is unclear from description, what the Peakvue data has indicated. Was there any defect frequency? Or random vibration? What were the numbers? Did post mortem analysis confirmed a defect in the bearing?

As far as increase in vibration after bearing replacement is concerned I think it is due to internal bearing misalignment introduced at installation. What kind of bearings are in there?

Thanks Mr.Shurafa & David,
1. True that the vibration levels are acceptable, as I had already mentioned - we are intending to bring the motor back to pre-overhaul levels ie about 1.2 - 1.5 mm/s.
2. The load run readings have been checked - the behaviour remains unaltered - no substantial change in vibration - 2.8 increased to 3.2 mm/s ( which I feel is not substantial - your views are welcome)
3. It is a 3.3 KV motor - Induction, Horizontal- with external and internal fans the cooler mounted on the motor.
Your assumption that it is horizontal motor is right
4. The service is critical - make Ansaldo

The NDE bearing 6316 had suffered wear in its inner race - there was evidence of initiation of spalls on the surface. The NDE bearing is not accessible and measurements were taken on the motor frame - when the peakvue increased we injected a few strokes of grease into this bearing while mointoring the peakvue - there was an immediate drop in the values - which increased back after a few days of operation. This initiated bearing replacement.

Bearings are deep groove ball bearings at both DE and NDE housings.

Your views please.


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