Bearing insulation on shaft
Bearing insulation on shaft
(OP)
Reading a past thread now closed "bearing insulation resistance test limits for INSTALLED motors"
Does anyone have the paper NETA paper that was given as a link. Is there any better guidance since this time on the subject.
We have marine electrical propulsion application where POD drive has been overhauled in dry dock. Bearings on bench are greater than 9gohm, installed back on shaft together with mechanical seals (could not be tested off shaft) resistance of shaft to ships hull is less than 500kohm at 100vdc test megger, multi suggests 300kohm. Pass criteria is 1mohm. Motor compartment assembly has been forced ventilated (normal compartment cooling not possible until pod housing reinstated) for few days on thought it was humidity but no change. Now at point where ship needs to come out of dry dock and great expense to return.
Any thoughts.
Does anyone have the paper NETA paper that was given as a link. Is there any better guidance since this time on the subject.
We have marine electrical propulsion application where POD drive has been overhauled in dry dock. Bearings on bench are greater than 9gohm, installed back on shaft together with mechanical seals (could not be tested off shaft) resistance of shaft to ships hull is less than 500kohm at 100vdc test megger, multi suggests 300kohm. Pass criteria is 1mohm. Motor compartment assembly has been forced ventilated (normal compartment cooling not possible until pod housing reinstated) for few days on thought it was humidity but no change. Now at point where ship needs to come out of dry dock and great expense to return.
Any thoughts.





RE: Bearing insulation on shaft
thread237-208967: bearing insulation resistance test limits for INSTALLED motors
(the NetaWorld Link within that thread doesn't work)
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(2B)+(2B)' ?
RE: Bearing insulation on shaft
http://www.maintenance.org/topic/bearing-insulatio...
Just a data point to add, applies to newly-refurbished motors (may not be particularly helpful if your goal is to understand the minimum reasonable for in-service motors
https://www.easa.com/sites/files/resource_library_...
We have one large non-vfd motor family where the OEM specifies 3,000 ohms, minimum. (i.e. 3kohms). That's the lowest I've heard. We have in the past accepted even lower readings on non-vfd large motors for specific circumstances and limited duration. I don't know whether special considerations apply to your application.
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(2B)+(2B)' ?
RE: Bearing insulation on shaft
As an example, I'm responsible for a legacy switchboard which has suffered heavy internal contamination from saline air and which is now disturbingly susceptible to atmospheric moisture. A maintenance team working all day exhaled and sweated enough moisture into the switch house to collapse the IR readings of the busbars, which then recovered overnight. We can't get the salt contamination out, so we're nursing this switchboard with permanent dehumidification until it is replaced.
RE: Bearing insulation on shaft
It was the only way that we could get leakage low enough.
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P.E. Metallurgy, Plymouth Tube
RE: Bearing insulation on shaft
Those who previously thought it was 'too difficult to release for maintenance' have radically shifted position!