Historical it has been used many different systems.
Halden had 40 Hz, Svalbard 25Hz, Rjukan had the 127/220V as you mention.
At home I have 230V 3 phase IT. When no errors in the network I measure 127V to ground. The 3 phase meter meters current in 2 legs.
At our cabin we have 3 phase 230V TT, I Guess this are tapped on the legs of a 400V transformer since the transformer was changed when some in the neighborhood built houses with 400V TN-C-S
The cabin are built on on solid rock, (in/on?? a little island of soil) In a dry summer its not good enough grounding to release the 30 milliamp GFCI when grounding a leg. I feel that's pretty safe. :-)
