The tubes you describe are almost certainly the large diameter T12 with older style 60 Hz ballasts. Since your ballasts are out, I recommend going to a T8 tube as they are available in 8' sizes. The T8 ballasts will be electronic, meaning higher efficiency and no flickering. The T8 tubes...
In more basic terms, the actual power generators produce 3-phase power because the machinery is in effect a large rotating motor. Customers that require a large electrical services are usually running lots of motors and the 3-phase power will operate those motors most efficiently. The phases...