I am curious to know how common this configuration is? I first ran into it in KC, where it is all over the place. They use 2 pole gear, makes for some simpler setups where you have a lot of meters and gear for a single building.
I saw it on sewer lift pumps. That was just a motor load in a remote area so it made perfect sense. Simple and cheap.
KC = Kansas City?
I find corner-grounded delta an interesting configuration, as it's something we've never (to the best of my knowledge) used over here, at least not unless it was perhaps employed in the very, very early days.
It makes perfect sense for saving extra switch poles, fuses, etc.
We have a term for corner-grounded delta around here... "ground fault!"
I don't know why corner delta seems so strange to people. We ground transformer taps and use them as current carrying legs all the time.
We use corner grounded 3 wire 3 phase xfmrs. all the time on pump jacks in the oil field.
Pauluk-Yes, the one and only Kansas City.
Steve F. please explain what you mean?
[This message has been edited by Almost Fried (edited 11-12-2006).]
I've never seen a corner-grounded delta used, but I have seen a lot of floating deltas on numerous switchboards. Naval ships use floating delta exclusively- even for single-phase circuits, both wires are "hot" legs of a 110/63V Delta. The idea is that if there happens to be a single phase ground fault, it won't interrupt power to the loads, and the worst a single-phase shock could be is 63V, which is especially important when you might be half-submerged in salt water at the time. I see it a lot in buildings, too, even some floating wye (with X0 ungrounded)- the reasoning is always the same; that a ground fault won't cause an unplanned outage.
So, when I hear talk of corner grounding a delta, I immediately think "Ground Fault!"
IT and communications. Often the switchboards and generators are 480V delta with local power supplies providing 208/120Y to the electronics. This creates some problems, as TVSSs and UPSs don't work properly on floating delta, and can malfunction if the delta drifts too far from center.
[This message has been edited by SteveFehr (edited 11-12-2006).]
Steve I am confused.
I work in lot of IT rooms and the supply to an IT room will likely be delta but it is from a 4 wire grounded Wye source and when it is converted down to 208Y/120 that is also grounded.
The only ungrounded systems I run into are in industrial buildings with motor loads and continuity of supply issues.
The 208V/120Y is always grounded wye, yes. The primary can be anything, though.
Naval ships use floating delta exclusively- even for single-phase circuits, both wires are "hot" legs of a 110/63V Delta.
Where does the 63V come from if the supply is a true delta configuration and there is no other ground reference on the system?
We use a 110Y/63V system on large building sites in the U.K. for the handheld 110V power tools. The secondary is wye though, and the neutral point is always grounded, thus limiting the potential on any hot leg to 63V with respect to ground.
There is no ground reference- when balanced, though, each phase will be 63V from the ship's hull, thus limiting shock potential to 63V. Calling it 110/63V is incorrect with that respect, I was just trying to demonstrate the point about safety. It's always simply referred to as 110V delta.
[This message has been edited by SteveFehr (edited 11-12-2006).]