Bearing ground ring

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hilltop

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Has anyone else heard of problems with induced voltage on the motor shaft due to uneven sinusoidal waves produced by VFd's that do not have filters installed?
These voltages are spikes that can break down lubrication to the bearings of a motor and cause fluting on bearings.
Our vibration analysis technician is reccommending we install ground rings on our motor shafts that are controlled by VFd's to dissapate these stray voltages that are damaging the bearings.
Apparently this problem has become more noticeable due to the lower costs of VFd's and their greater number of installations.

Any comments?????
 
Motor Bearings and VFD's

Motor Bearings and VFD's

hilltop said:
Has anyone else heard of problems with induced voltage on the motor shaft due to uneven sinusoidal waves produced by VFd's that do not have filters installed?
These voltages are spikes that can break down lubrication to the bearings of a motor and cause fluting on bearings.
Our vibration analysis technician is reccommending we install ground rings on our motor shafts that are controlled by VFd's to dissapate these stray voltages that are damaging the bearings.
Apparently this problem has become more noticeable due to the lower costs of VFd's and their greater number of installations.

Any comments?????
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I have heard of this problem. I was at a motor rewind shop years ago and was told they actually install an insulator around one of the bearings breaking the circuit of the stray currents that cause the pitting. I am not sure if inverter duty motors come with that feature or not. I would contact a motor shop and see how they are dealing with the issue.
 
Motor Bearings

Motor Bearings

I just did a quick check and the Inverter duty motors do come with insulated bearings and on the larger size motors they have a grounding ring of some kind. I would suggest checking with a motor shop and seeing what modifications would be best for your specific motors. In some cases you may want to replace the motor and others maybe a modification will solve the problem. Its all about cost.
 
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