Insulation bearing for MV/HV motors

[ElecEE8]

Is it mandatory to provide insulation bearing for all MV and HV motors? There are regularly failure reported in oil&gas and petrochemical plant on bearing failure of MV and HV motors nowadays. Any best practice available in design & engineering /or lesson learnt in your place, please share.

 

[edison123]

It is recommended to insulate against shaft currents that damage the bearings for motors with white metal bearings and for motors running on VFD. The insulation system is OEM and motor specific.

From one OEM -

https://www.google.com/url?sa=t&rct...Zl87eAhUZeH0KHYN6AKMQFjABegQIBBAC&url=http://

http://www.brookcrompton.com/upload..._GAMBICA.pdf&usg=AOvVaw2GCw3Vu4_pWIJWYCDmFpJv

Muthu

http://www.edison.co.in

 

[electricpete]

For vfd driven motors, I believe it is advised to insulate or otherwise protect bearings, regardless of motor size. The reason is that the high frequency components are capacitively coupled accross the airgap.

For non-vfd driven motors, that high frequency component is not a concern. In this case, it is generally only required to insulate bearing when the motor is big enough to require segmented core laminations (I think that is greater than 40" diameter stator core). The reason is that gaps between segmented laminations introduce the potential for a flux imbalance which would induce circulating currents (applies to both rolling and sliding bearings). In this situation (non-vfd large motor), insulating the outboard bearing alone is enough to interrupt any circulating current path around the core and protect the motor and driven equipment. However that makes it difficult to test the insulation. If you insulate both bearings, then you can test the insulation periodically (when motor is uncoupled) to verify the insulation is still intact.


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(2B)+(2B)' ?

 

[ElecEE8]

Thank you all for your replies.