Coupling failure Risk in VSD motor driven Lobe type blower
Coupling failure Risk in VSD motor driven Lobe type blower
(OP)
Guys,
We have VSD motor driven Lobe type blower.Due to nature of process, this blower can see large and quick swings in the speed output. Its also a fairly large motor(1000 HP) and being a lobe type there’s quite some mass on the coupling end.Does these quick speed changes creates any risk for coupling failure due torsional vibrations
We have VSD motor driven Lobe type blower.Due to nature of process, this blower can see large and quick swings in the speed output. Its also a fairly large motor(1000 HP) and being a lobe type there’s quite some mass on the coupling end.Does these quick speed changes creates any risk for coupling failure due torsional vibrations





RE: Coupling failure Risk in VSD motor driven Lobe type blower
As for torque, you need to size the coupling for the expected loads, including accelerations.
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P.E. Metallurgy, Plymouth Tube
RE: Coupling failure Risk in VSD motor driven Lobe type blower
Johnny Pellin
RE: Coupling failure Risk in VSD motor driven Lobe type blower
RE: Coupling failure Risk in VSD motor driven Lobe type blower
Please help me with questions that need to be asked to OEM to make sure that we will be in safe position as far as coupling failure due torsional resonance is concerned. Apart from torsional analysis ,what are data /documents that can be asked to OEM that confirm that there will be no torsional resonance.
RE: Coupling failure Risk in VSD motor driven Lobe type blower
Johnny Pellin
RE: Coupling failure Risk in VSD motor driven Lobe type blower
Nevertheless I'll try to talk through the way I look at it.
There are two distinct aspects of a torsional resonance:
1 - excitation of resonance with a discrete forcing function at the resonant frequency
2 - exciting the resonance by a broadband / impulse-like forcing function (analogous to ringing a bell or impacting a structure for vibration bump test).
Scenario 1 requires a speed-dependent torsional excitation to be relevant to this discussion. For a given set of endpoints, rapid change in speed is better than slow change in speed with respect to exciting a torsional resonance (it's better to pass thru a resonance fast than slow… if endpoints are resonant than either case is equally bad). So I guess scenario 1 is not really relevant to this discussion.
Scenario 2 requires something like an impulse in torque. That could maybe be a rapid speed change. In that case the oscillation does not persist long after the transient. For a give speed change what determines how large the oscilation is and how long it lasts is heavily dependent on torsional damping. What type coupling is it?
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(2B)+(2B)' ?
RE: Coupling failure Risk in VSD motor driven Lobe type blower
RE: Coupling failure Risk in VSD motor driven Lobe type blower
You describe the coupling as a diaphragm design. But, the drawing provided looks more like an elastomeric coupling. A diaphragm or disk pack coupling would not have much damping for torsional vibration. An elastomeric coupling would tend to have more torsional damping. The coupling design would play a major role in the analysis for torsional resonance response.
Johnny Pellin
RE: Coupling failure Risk in VSD motor driven Lobe type blower
I hijacked the discussion toward trying to figure what implications of torsional resonance are with respect to rapid speed change. Now I rereadJPellin's comment and see it was just about torsional resonance in general not associated with any rapid speed change.
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(2B)+(2B)' ?
RE: Coupling failure Risk in VSD motor driven Lobe type blower
RE: Coupling failure Risk in VSD motor driven Lobe type blower
Quote: For a given set of endpoints, rapid change in speed is better than slow change in speed with respect to exciting a torsional resonance (it's better to pass thru a resonance fast than slow… if endpoints are resonant than either case is equally bad)
Mean by endpoints is speed setpoints here??
RE: Coupling failure Risk in VSD motor driven Lobe type blower
diagphram coupling will have relatively low torsional damping.
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(2B)+(2B)' ?
RE: Coupling failure Risk in VSD motor driven Lobe type blower
There are two main types of coupling vibrations and resonances that we concern ourselves with. 1st is when we have a lateral resonance, this is typically associated with longer span couplings operating at or near their critical speed. This is where rapid changes in speed can help you get through the critical speed limitations. I don't think that is what you are dealing with in your application. The other main cause of vibration is due to Vibratory torques, these vibratory torques occur when when the load and driving equipment are essentially fighting each other. Many times this has to do with various operating speed points in an application. We typically see this in reciprocating compressor applications where speed is changing and the load is vibrating due to the nature of the compressor. In your case with a blower, there are natural vibrations that will occur due to the physical design of the blower and how it moves air at various speeds. Most often times Blowers are less troublesome then compressors. However, your selection of a Neupex coupling does concern me slightly, the rubber elements that are in that style coupling are designed to eat energy as well as flex for misalignment and in your application they could wear out quite rapidly. This could cause a lot of maintenance and down time. We typically see Gear couplings for type of application, and if you are looking for a long life low maintenance solution go with a disc coupling with flexible metallic elements.
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