Dear, these days I'm facing on several motor vibration problem. This is one of them. I want to hear your opinions.


the motors vibration amplitude for multi stage pumps was raised up from 3 to 9 mm/sec RMS for this year. 

On the FFT, 1X horizontal vibration is dominant about 90% of overall value. And this motor vibration is transferred to motor base - foundation - concrete floor and near same machine motor that is still power off but vibration is about 1 ~ 1.5 mm/sec.

Is it motor unbalance problem? already motor overhauled and checked weight balance. 

Is this vibration was effected due to motor base plate stiffness? Motor base was fabricated channel looks like weak for this heavy motor. But 9 month ago vibration was not high like recent and there is no evidence of base crack for welding point.

Is this vibration was effected due to electrical things? Why does power off motor have vibration? 

( Motor : 337kW, 2P, 6600V, 60Hz, 2450Kg, Bearings 6218C3)




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Original Post

If you still have vibration without power to the motor, then something running near this motor is causing that vibration.  For a motor to change vibration over time, several things are possible:

The motor base may have settling issues causing a rigid body mode to move closer to running speed.

The motor could have thermal issues causing rotor bow.

If there is vibration close by, check that out first

Generally speaking the box channels used like this are quite stiff as long as the underlying base is solid ( no grout issues or cracked welds). I would do a bump test on the base in 2 directions to see what the natural frequency is and isf it is close to the running speed of the motor. If that isn't the driver then you can move on to other possible causes. What does the pump vibration data look like? What type of coupling?

Yes, motor NDE foot was not supported with wider shims. I agree with you Mr.Brook.

to RGF12

Pump vibration is maximum 1.0 mm/sec RMS. It's very stable. And coupling is flexible disc type.

to all

At first, we added beams for increasing horizontal stiffness as like pictures. And motor - pump was re-aligned by laser tool again. Vibration amplitude was reduced. Now it shows about 5mm/sec RMS. 

But motor still has strong 1X vibration. And motor terminal box, cable, paved floor and the others still have same vibration. Especially we can feel buzz sound from the paved floor and it have periodic time 2~3 seconds. And we will do bump test for resonance. 


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If you have a beat frequency, that is proof that there is something else running near the same speed that is added and subtracting to the vibration at 1x.  Check all equipment neat this motor.

Have you checked the alignment yet?  Have you soloed the motor?

Sometimes the high vibration on the horizontal direction is  caused by the vertical direction. Just type "weak base" in Google and look for a Siemens paper. ( With some measurements at the feet, base and bearings house you can confirm this hypothesis, phase measurements are highly desirable. Left and right measurements  will be in counter  phase. If it is your case, your need reinforcement in the vertical direction. Again, measure feet, base (in many points as possible) until you find a member that is not moving together (same intensity and direction, i.e. amplitude and phase). Sometimes is matter of the location of the structural beam, which you are not seeing (under the plate). 

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