We regularly replace bushings and bushing gaskets onsite at our power station, and I would agree with the points listed above by prc and Jay27.
Typically once the transformer is proven de-energised, the biggest risk we need to manage is of oil spills and subsequent environmental cleanup issues...
I should have also mentioned that the problem of "copper dusting" as described above is not a problem at rated speed because the copper windings are held in position by the large centrifugal forces pushing them onto the wedges and retaining rings.
Yuma
I work for a generation utility and we recently mothballed 4 x 40 yr old Parsons 60 MW, hydrogen cooled only turbogenerators. The seal and lube oil systems were de-commissioned while the underbelly heaters remained in-service. We left the rotors in situ and did not seal the generators in...
