Bearing failure, motor or pump?
Bearing failure, motor or pump?
(OP)
If you have a centrifugal pump, inverter duty motor and VFD, which bearings has the highest risk of failure(motor or pump), what kind of failures is expected and what are the steps needed to prevent these type of failures.
Are there any features that can be added when ordering the motor and the pump in order to reduce the risk of failure?
I talked to dealers about insulted bearing in inverted duty motor; one said is not needed and another said is only a myth.
I found some articles about the of PWM drives on bearing and general bearing failure but I still looking for article about the effect of centrifugal pump on Motor bearings and vice versa. if you have any reading materials about subject feel free to add them.
Thanks in advance for you suggestions and advices.
Are there any features that can be added when ordering the motor and the pump in order to reduce the risk of failure?
I talked to dealers about insulted bearing in inverted duty motor; one said is not needed and another said is only a myth.
I found some articles about the of PWM drives on bearing and general bearing failure but I still looking for article about the effect of centrifugal pump on Motor bearings and vice versa. if you have any reading materials about subject feel free to add them.
Thanks in advance for you suggestions and advices.





RE: Bearing failure, motor or pump?
Most bearings fail from lubrication problems, either not the right type, too much, too little, water or dirt contamination. Only a small fraction actually reach their design life. What to do depends on the size of the pump and the type of lubrication. For grease, using an automatic lubricator helps prevent all the problems mentioned, for oil, a good circulation system with filter will go a long way to prolonging life. Then of course make sure the pump is installed correctly. A good firm base, proper alignment, no pipe strain, etc.
RE: Bearing failure, motor or pump?
I was not very clear before; the myth is not about the electrical fluting but about insulating the bearing to solve the problem. I think the dealer agree with you that is better to prevent the problem with good grounding and electrical installation than putting an insulation.
do you have an idea if the bearing failure are more frequent in the pump or in the motor that drive it (vertical motor)?
Thanks,
RE: Bearing failure, motor or pump?
Sorry for the vague answer, but there are so many factors involved to give an answer one way or another.
As for the insulated bearings, they stop the arcing through that bearing, but may cause another problem elsewhere. You can use either ceramic balls or insulated coated bearings to isolate from the housing, but if you do not then take into account the voltage will want to find an alternate path, you might actually make your problem worse. By isolating the motor bearings, the current may find a path through the pump bearings and destroy them instead. My advice would be to run the motor with the normal bearings and install a shaft grounding ring to drain the voltage to ground or install a filter between the VFD and motor to minimize the high frequency pulses that are the causes of the flutting. Which way you decide to go will depend on how big the motor is and the costs of each strategy.
This article might be helpful in what you decide to do.
http://www.hpac.com/GlobalSearch/Article/47488/
as well as this one
http://www.eng-tips.com/viewthread.cfm?qid=102205
RE: Bearing failure, motor or pump?
"Correct installation" is a myth - I would say. And so is "Correct grounding". It all depends.
There are three main failure mechanisms with motors and VFDs: Induced shaft voltage, Capacitively coupled shaft voltage and Frame voltage due to bad grounding/long PE.
The induced shaft voltage is most common in large motors - like 300+ HP while capacitively coupled shaft voltage is more common in small motors. Frame voltage can be a problem regardless of motor size.
If your motor is a fairly large one, like 300 HP and up, the motor bearings are at risk. But not only the motor bearings, the pump bearings can also have EDM. Especially if the coupling is conductive.
Insulated bearings have a limited sucess in preventing EDM. That is because the HF components in the PWM waveform pass through the rather high capacitance of the Al2O3 layer that constitutes the insulation. Typical capacitance values are between 2 and 20 nanofarads for motor bearings.
My advice is that you shall do some reading yourself and try and understand the problem. There are too many "knowing" persons telling you whatever she/he has misunderstood. And that is particularly true in this field.
Google EDM (Electric Discharge Machining, which is the term for bearing damage through electric erosion). That will give you a good start.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Bearing failure, motor or pump?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Bearing failure, motor or pump?
A very good option for critical applications.
RE: Bearing failure, motor or pump?
A flyer on bearings with cermamic elements:
http://
This one has pictures of bearings with fluting damage:
htt
Disclaimer- I do work for Koyo but the information above is pretty general.
RE: Bearing failure, motor or pump?
1. Why would you install a VFD on a centrifugal pump? The pump is designed for the requested head and flow caracteristics. You will miss the BEP with a VFD.
2. There are no bearings in a vertical pump! They have guides (bushings) and wear rings.
3. Flow on a vertical centrifugal pump is controled by a bypass line or pinching in the discharge valve.
4. The most problems will come from the seal. Mechanical or stuffing box. Be sure to get the flush lines right, if any.
Hope this helps.
RE: Bearing failure, motor or pump?
Getting back to the original post, there are a host of possibilities, but in order to discuss the correct ones, you'll need to give more details.
Here are a couple of thoughts:
If the VFD allows the pump to run under no flow/deadheading conditions, you can expect the pump bearings to give you trouble.
If the VFD allows the pump to operate at a critical speed, you can expect the pump bearings to give you trouble.
RE: Bearing failure, motor or pump?
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