I think something like this wins that category:
https://en.wikipedia.org/wiki/Eastern_Interconnection
It's strange to count this as single machine. But if we go this way, the north Chinese interconnection and the continental Europe interconnection are bigger (https://en.wikipedia.org/wiki/Wide_area_synchronous_grid).
I suppose it's partly a semantic question that hinges on what you count as a single "machine" and what's a system or a network.
The fact that there’s more than one copy of TWINSCAN EXE 5k seems important
It's strange to count this as single machine. But if we go this way, the north Chinese interconnection and the continental Europe interconnection are bigger (https://en.wikipedia.org/wiki/Wide_area_synchronous_grid).
I suppose it's partly a semantic question that hinges on what you count as a single "machine" and what's a system or a network.
The fact that there’s more than one copy of TWINSCAN EXE 5k seems important