Paul, there some states that are not connected to the US grids. This is a result of the New York blackouts back in the 60's. Howevewr it does not mean they are intercconected.
When I worked for a utility in Oklahoma we interfacerd with Texas utilities via DC. We entered the yard at 138KV AC, rectified to DC, had a bus to the the Texas utility, they inverted back to 138KV AC all in the same substation.
