wilans
Member
- Location
- Asia-Pacific
anybody can help giving advice how to eliminate or at least minimize motor bearing current during the motor is running ( in operation )??
Thnx,
Rgds
Thnx,
Rgds
motor bearing current elimination technics during the motor is still running
- Thread starter wilans
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I think there is some kind of doohickey sold to short out that current.
- Location
- Massachusetts
I have seen just grounding brushes put on the motor shafts but that can only divert some of the current from the bearing.
I think the most effective solution is the grounding brushes on the motor shaft and changing the motor bearings to ceramic coated bearings so that they do not create a path between the armature and ground.
I think the most effective solution is the grounding brushes on the motor shaft and changing the motor bearings to ceramic coated bearings so that they do not create a path between the armature and ground.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
There are shaft grounding bushings that can be installed into the motor, many "Inverter Duty" motors come with them now. But there are externally mountable shaft grounding systems that can be retrofitted. The problem is, there are a LOT of different configurations of motors, shafts and ways to mount it, so you are going to have to find an expert and have them look at your specific situation to recommend a solution that will work for you. Do a search on "Shaft grounding systems" in your favorite search engine.
- Occupation
- Licensed Electrician
We had somebody ask us about using ceramic bearings on the motors for their air handlers.
The rumor was that the VFD's were eating the bearings. Problem turned out to be belts that were waayyyy to tight so we didn't install them. How well do ceramic bearings work? Are they difficult to work with?
wilans
Member
- Location
- Asia-Pacific
thanks for the responses.Any facility to install the grnding brush while motor runing
thanks for the responses.Any facility to install the grnding brush while motor runing
Anyone has eperience to install the grounding brush during the motor is running. This motor is very critical to the Plant. No chances to stop it. The plant turn arround schedule is still long.
thanks for the responses.Any facility to install the grnding brush while motor runing
Anyone has eperience to install the grounding brush during the motor is running. This motor is very critical to the Plant. No chances to stop it. The plant turn arround schedule is still long.
wilans
Member
- Location
- Asia-Pacific
Anyone has eperience to install the grounding brush during the motor is running. This motor is very critical to the Plant. No chances to stop it. The plant turn arround schedule is still long.
I haven't installed any of the Aegis or other motor grounding brushes myself, but knowing the general construction I can see no possible way to safely install them without the motor stopped, isolated, and locked out. If the bearing currents are sufficiently high that you are contemplating a grounding brush and this motor is highly critical, I assume you have a spare motor onsite to you can swap the motors quickly rather than having to wait to replace the bearings on the critical motor. I would suggest fitting your spare with the grounding brush. If you don't have a spare then it's probably not as critical as you think, but in that case procure the proper grounding brush and put it in the storeroom with the replacement bearings so you can install it the next time the bearings fail.
weressl
Esteemed Member
Grounding brush equipped bushings are commonly available as posters recommended and they work. Have to remember to replace them and periodic resistance measurement, as part of maintenance, is in order to detect failure.
Circulating shaft currents have their origin in magnetic imbalance of the three phases that is due to manufacturing tolerance of winding and core and supply voltage imbalance. ASD's tend to greatly magnify the effect but it is present to some degree in all asynchronous machines.
It is somewhat puzzling that whereas this was a recognized problem with large motors, manufacturers report an increasing number of damage on smaller motors <50HP. Could it be the greatly increased use of drives, or is it carrier frequency related or perhaps drive end technological change?The jury is still out on this issue. On large machines, when you specify inverter service, manufacturer will supply insulated bearing on one end and some places a grounding brush-bushing on the opposite end.
I had this issue on an 800HP machine ASD retrofit and just installed a beryllium/copper strip spring riding on the shaft, a home-made brush if you will. This was long before commercial items were available.
Lastly, these can not be used in hazardous locations. Of course one asks what happens to the arcing within the bearing that is perhaps even higher energy discharge than the brushes would produce.:lol: The respective IEEE motor standard committees are still scratching their heads, so far, on this issue.
This is interesting, especially since the NEMA frame motors are mass produced in such large quantities to tolerances sufficient to meet .08 ips vibration (IEEE 841) or even .04 ips vibration (GE's IEEE 841 line). One would think that the magnetic asymmetry would be minimized by the automated manufacturing processes.
Another one of the great mysteries - just like how we have T-ratings and maximum permissible surface temperatures on electrical equipment but a 600# steam line with a surface temperature above the AIT can run through the process area....
weressl
Esteemed Member
Squeeky wheel gets the grease. When users start complaining about the magnetic imballance maybe some efforts will be made to tighten up those too. However the voltage imbalance will still remian a problem. Some manufacturers seem to do better than others in this aspect, but there is no info or statistics available on this issue.
Motors do not have T-rating stamped on them, nor do they need to have, but some manufacturers make the maximum design surface temperature available. The 600# steamline should NOT run through the process if the PHA was done properly. I have more of an issue with the Electrical Classification process which should be part of formal PHA.
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