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Several years ago, Niagara Mohawk had an exhibit building at the Erie County Fair (Hamburg NY). On display were various types and sizes of high tension insulators. The guide explained high voltage power transmission-- generalizing, of course. He did mention the set of 450kV lines that run the length of New York State are the highest voltage lines in use in North America (circa mid-1990's). He did say that NiMo built an experimental 900kV line near Syracuse NY, but the line was never energized, not even as a test. I want to know why? Was the whole thing just impractical because the 450kV lines are doing a fine job? Or did they fear something Tesla-onian might happen at such a hyper-voltage? E-mail inquiries to NiMo have gone unanswered.

There are several 1,000kV {one megavolt} DC lines in routine service on the North American continent. The upper end for 60Hz is generally 1,200kV AC (UHV class) but not considered technically [and economically} practical.

For 60Hz, the functional maximum in IEEE Standard 1312 is 800kV {3ø} with a nominal rating of 765kV (EHV class - includes 345 and 500 kV).

Georgia has had 500 kv transmission lines since about 1972, so I think the NiMo source is incorrect.

I'm not questioning whether or not lines in excess of 450kV are in use. I'm just amazed at NiMo's abandonment of the project. What were their reasons?

500kV in use up here in BC, Canada... since 1968
http://www.bchydro.com/info/system/system15244.html