Shaft currents
- Thread starter hawkeye23
- Start date
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renosteinke
Senior Member
- Location
- NE Arkansas
It's possible.
Most often, the proof is found when the bearings fail; then you can see signs of arcing, etc.
There are a variety of products and approaches that address this issue. Some motors are designed for VFD use, in part by insulating the bearings from the shaft. Another approach is to have copper brushes in contact with the shaft, giving the electricity as better path to ground.
Most often, the proof is found when the bearings fail; then you can see signs of arcing, etc.
There are a variety of products and approaches that address this issue. Some motors are designed for VFD use, in part by insulating the bearings from the shaft. Another approach is to have copper brushes in contact with the shaft, giving the electricity as better path to ground.
tish53
Member
- Location
- richmond, VA
I have experienced electric fluting on bearings numerous times. My experience has been on 400 and 600 hp motors run from VFD's. The cause is a phenomenon called "common mode noise" that induces a voltage on the motor shaft which if it gets high enough will arc through the bearing grease and result in a fluting pattern on the bearing race. It varies with all the parameters of the installation. cable type, distance of motor from VFD, grounding methods, VFD type. Larger motors seem much more likely to have problems.
Some VFD manufacturers address this with a "common mode "filter ( normally only in their higher cost, engineered system VFD's). You could contact the drive manufacturer and see if they have a solution.
Another approach is to outfit the motor with a shaft grounding brush to bleed off the voltage so it will never get high enough to arc across the bearing. If the motor has bearing damage and is out for repair, then the most cost effective solution could be the shaft grounding brush. The motor shop can add it in. One issue to consider is the shaft grounding brush will wear and eventually need replacing. We have seen long life (5-7 years) on some of our shaft grounding brushes but still try to put it in a place we can inspect and change as needed.
Some VFD manufacturers address this with a "common mode "filter ( normally only in their higher cost, engineered system VFD's). You could contact the drive manufacturer and see if they have a solution.
Another approach is to outfit the motor with a shaft grounding brush to bleed off the voltage so it will never get high enough to arc across the bearing. If the motor has bearing damage and is out for repair, then the most cost effective solution could be the shaft grounding brush. The motor shop can add it in. One issue to consider is the shaft grounding brush will wear and eventually need replacing. We have seen long life (5-7 years) on some of our shaft grounding brushes but still try to put it in a place we can inspect and change as needed.
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