I would have ordered full testing for the transformers, even though they’re saying there were no events that would indicate a problem with the transformer itself during the blackout. It’s easy to do and does not take more than half a day. The fact that the 87(differential function) tripped twice during energizing means that there is no restraint function on the protective relay or it’s settings were not correct. If the transformer is healthy those trips should not have happened.
I noticed quite a few non-standard terms used in the report. Whoever wrote it doesn’t sound familiar with this type of equipment. I wouldn’t expect them to be either. They should have involved a US based testing company. I’m not casting any doubt on HHI, but having HHI alone testing is a pretty clear conflict of interest IMHO.
Neither the preliminary report nor the new test report state what, if any, events were recorded on the protective relay for HR1 at 0125 at the time of the initial blackout. If nothing was recorded, other than breaker open, then that would point to the UVR.
The more I read through these reports, the more I’m starting to think NTSB is out of their depth in this type of testing. They really should have brought in an experienced, independent third party.