decreasing induction motor vibration

[350Z]

I'm having problems with vibration at certain speeds ( especially at slow speed)on my 3 phase, 4 pole AC induction motor & I'm trying to find methods of reducing the vibrations. The motor is driven via Vector control and I'm wondering if changing the carrier frequency would make any different? I need to work the full range of the speed and skipping frequency is not an option. I do not have a lot of latitude on changing the physical and guts of the motor design and construction.Also does changing the number of poles reduces the vibration of the motor? Any suggestion?

 

[electricpete]

It is always helpful to know the frequency of the vibration (1x running speed).

Is it possible that you are hitting resonances of the motor as mounted. Usually more likely if the vibration is highly directional... i.e. all in the horizontal direction, much less in vertical.

With the motor vibrating at the problem speed, try adding weight or temporarily bracing the motor... if reduces vib that may indicate resonance. There may be a variety of fixes available in that case.... adding permanent weight to the motor, adding permanent stiffeners, adding dynamic absorber (frowned upon), changes to mounting configuration.

 

[moturcu]

Hello 350Z,
It looks like you have mismatch between motor and inverter.
You may try adding inductance to the inverter output to reduce the carrier frequency related components.

If this is not possible you may increase the carrier frequency so that motor inductance can be effective. However this may increase low-frequency harmonics and related vibration.

As a last suggestion you may decrease your dc bus voltage if it is possible. By doing so you will force the inverter to increase the modulation index and reduce the amplitude of the carrier frequency related components.

 

[GusD]

Hello 3502

You are already assuming a lot of things related to your Vector drive.The fact that it is a vector drive and VFD does not necessarily makes it a vibration Generator.You already believe that carrier frequency may be the problem,but I don't know if you can be sure of that.
When we perform Vibration analyses on rotating equipment ,we look for specific frequencies that will direct you to the problem.At least,it is the premise.Very seldom do we look at a vibration problem and the first thing we assume is that it must be the VFD or inverter related.
In any plant,yours and mine,the culprit for hi vibs most ot the time is misalignment .Unbalance comes right behind.Trow in soft foot,resonant conditions and a few others and your Motor/VFD problem may not even make the list of reasons.
Let me know how you made out after you changed your Carrier Freq.Wish you luck

Thanks
If your motor operates at 60Hz,do you have a lot of 120 hz Vib peaks, or 180 hz or anything that can be related to the drive or the motor.You don't offer nay freq.values so,it is hard to know what you talking about.
There2

GusD

 

[jbartos]

Suggestion: Traditionally, the motor-load set is analyzed for vibration as a set. The analysis should include a process of elimination by analyzing the motor and motor load separately.