Very interesting test you have done there Brian.
Exactly what you show there is what happens in the real world.
I deal a lot with intermittend HT faults on 11 kV transformers. Dirty bushings cause a flasover, blow HT fuse. I always insist that the line crews disconnect the 11 kV cables prior to do an insulation test on the cable because of that reason.
I will do a similar test with a 5 kV megger, to show some of our fault staff why cables and bushings have to be clean.
Thanks for those great photo's
The product of rotation, excitation and flux produces electricty.