Dnk,
The size of the transformers, the balancing of the loads, the heat they put out, the size of the wiring neeeded, and the power consumed(on a demand basis), are all down sides to that idea....
Maybe, but you elimintate the costs of "super neutrals", K-rated transformers, double neutral bus and things like that. I don't think that you would have any more heat as all of the heat from the harmonic loads is gone. The balancing is not any harder than with the 3 phase system.
That being said I wouldn't do anything special... there is just no documented evidence of a big problem with non-linear loads....just a lot of theory and a lot of products in search of a problem.
Don
