Carbon on grounding in Motor conduit box - Troubleshooting

[FishR]

The physical integrity of the grounds seems in good shape but the problem seems to reside there. The tape job is removed in the pictures. The connections were all tight and the phase conductors were clean. Both sleeve bearings are insulated. Motor is 2400V, 3 phase, 3600 RPM, 600 HP. It is started on SCRs then runs across the line. Cables megged great and so did motor. In the next few days we will verify the SCRs are good and cut these terminations open to inspect. I don't believe either is the problem but I have to rule them out. Anyone have any ideas what would cause this? The fact that there is not a specific point of tracking or evidence of partial discharge has me stumped.

 

[charlie k.]

That looks like the effects of Hydrogen Sulfide. Is this motor located in a Waste Water plant?
I would not take your high voltage terminations apart if it is.

 

[kwired]

I'd also agree with something in atmosphere is reacting with the copper. Your insulated conductors are protected by their insulation and are probably not doing this.

 

[FishR]

Clean atmosphere

Clean atmosphere

The motor is outdoor and in a clean atmosphere. I do agree that it does look H2S or sewer gas. To add to the point, nothing is "corroded" on any of the connections but ground.