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Regarding FP&L do you have a picture? Never seen that done before but it is possible they are doing it- a million flavors for everything exist in the US lol.
No sorry, I think it was late 80's early 90's when we were installing some chp schemes in the US, when I last actually worked on it, no mobile phones then!
They were all 13.8kv generators, and nothing appeared odd at first - 13.8kv is a 3 wire system it appears, however it got back-fed via the 4.16kv system that is 4 wire, and cross connected different phases from different lines to give a three phase transformer supply, scared the "xxxxxxx xxxx" out of us.
Was back over with fhp probably about 15 years ago, and mentioned it to the engineers I was with and they said it was fairly common still.