Hi Trumpy:
My understanding of that type of switch is that the SF6 interrupters do the actual load make and break, they operate at a very high speed. The arms are to provide a visible break and substantial clearance to prevent arc restrike.
Since the one bottle failed in this situation it allowed the arc to form.
The arm travel on my highspeed connection with the video going normally takes about 3-5 seconds.
The reclosing sequence goes something like this: reclose commanded-bottles contacts open-arms close and seat-bottles reclose.
This was also at a very large power plant (not a substation as mentioned) so I'm willing to bet there is a fence around the whole switchyard.
Footnote: Anyone curious about these kinds of things should get the book I have, "Standard Handbook For Electrical Engineers" (Thirteenth edition) Authors Donald G. Fink/H. Wayne Beaty; Published by McGraw Hill. Might have a later edition out by now, mine is several years old.
It has a lot of information and comprehensive section on transformers including maintenance recommendations.
