Not difficult to explain Redsy, perhaps Scott can be imposed upon for a schematic.
The transformer (called "Buckets", "Pots" and a host of other things by crews) are simply constant current variety. Typically they provide 20 amps steady current to the series circuit, open circuit voltage can be 2200.
The shunts are there on the other side of the individual lighting transformer (that is there to limit the amount of current that an individual light may draw)so that a single light fixture failing will not put the entire circuit in the dark.
Airports use this type of lighting for the simple reason that all lights are the same intensity at all times, works that way on the street lighting as well.
In other words, no light is brighter than the one beside it.
Simple system, tough to get your mind around. Your system can "shoot grounds" and still work perfectly well while being damned dangerous, wierd, huh?
If you're foolish enough to pull a ground wire in a pipe with your ungrounded conductors, your not gonna like what you get, even though it sure feels like you are complying with the code, it makes the situation extremely dangerous. That's about the worst thing that can go wrong.
And you also feel like a complete Dumb A** when you roll up to a transformer at 2 am, throw an amprobe on it and say "Must be working, it's got a 20 amp load on it"
DOH, of course it's got a load on it, if it were shorted completely out and burning it would IT'S A CONSTANT CURRENT TRANSFORMER!!!
Not that this ever happened to me, of course..