Transformer Comparison for 240VAC 3 Phase Loads

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Jbyars

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Sunray Texas
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Associate Electrical Engineer
I have several 230V 3 phase saws and carpentry equipment that are being relocated to a new building that will require a new power supply to.
There is an existing 208Y/120 VAC panel in this building that feeds lights and receptacles, but after discussion with equipment manufacturers they recommend not running the equipment at 208VAC.

We have 480VAC 3 Phase available in the area, and I am evaluating transformer options to resupply these loads and have come up with 3 different secondary configurations that I am trying to decide between.
1. 240VAC Delta corner grounded
2. 240VAC Delta center tap
3. 240Y/139 VAC

My question is what are the advantages/disadvantages of each configuration type?
 
The ungrounded would likely be the worst choice since you would need ground-fault monitoring and drives don't care for ungrounded systems
I would go with the 240 Delta Center tap. Some equipment now or future may need the neutral and the transformers are fairly common if a replacement is needed,
 
If the saws have VFDs on them, you want the 240Y139 transformer, otherwise, the center tap delta is fine. They are more useful later if something changes.
 
Jraef said:
If the saws have VFDs on them, you want the 240Y139 transformer, otherwise, the center tap delta is fine. They are more useful later if something changes.
Click to expand...
Not challenging in any way (that would be blasphemy).. just curious, why ??
( I lead a sheltered life ;) never saw a 240/139)
 
augie47 said:
The ungrounded would likely be the worst choice since you would need ground-fault monitoring and drives don't care for ungrounded systems
I would go with the 240 Delta Center tap. Some equipment now or future may need the neutral and the transformers are fairly common if a replacement is needed,
Click to expand...
I had already ruled out the ungrounded delta due to the potential hazards associated with that system.
I was leaning more towards the center tap delta anyways since I have had more exposure to them, but I just wanted to weigh my options.

Jraef said:
If the saws have VFDs on them, you want the 240Y139 transformer, otherwise, the center tap delta is fine. They are more useful later if something changes.
Click to expand...
None of the saws have VFDs, but there is a Bar Bender that has one.
What would the risk be if I went with the center tap delta to power this Bar Bender?
 
It's just what the L-V voltage is from a 240v L-L wye. The only purpose for it is to provide a simple-to-ground 240v 3ph.
 
Jbyars said:
None of the saws have VFDs, but there is a Bar Bender that has one.
What would the risk be if I went with the center tap delta to power this Bar Bender?
Click to expand...
VFDs usually these days have MOVs on the power input. Usually at least some connection from phase to ground somewhere. If it is ungrounded you have the potential to go well above the voltage rating of the MOV from phase to ground.

Some VFDs give you the option to disconnect MOVs that might have such a problem.

You would have the same issue with corner ground or center tapped.

Your best option with drives is a solidly grounded wye power input.
 
augie47 said:
The ungrounded would likely be the worst choice since you would need ground-fault monitoring and drives don't care for ungrounded systems
I would go with the 240 Delta Center tap. Some equipment now or future may need the neutral and the transformers are fairly common if a replacement is needed,
Click to expand...
A delta center tap system does not have a neutral. It does have a small amount of capacity to deliver 240/120 power. the grounded conductor in this type of system is not a neutral though.
 
petersonra said:
A delta center tap system does not have a neutral. It does have a small amount of capacity to deliver 240/120 power. the grounded conductor in this type of system is not a neutral though.
Click to expand...
You don't consider the tap to be a neutral? It's not equal voltage from all lines, but that's not "the" definition of one.
 
Jbyars said:
We have 480VAC 3 Phase available in the area, and I am evaluating transformer options to resupply these loads and have come up with 3 different secondary configurations that I am trying to decide between.
1. 240VAC Delta corner grounded
2. 240VAC Delta center tap
3. 240Y/139 VAC
My question is what are the advantages/disadvantages of each configuration type?
Click to expand...


You said you already have a 208Y/120 VAC panel feeding lights and receptacles. Assuming that you keep this for such loads, what would be the advantage of a center tapped (high leg) delta for you over 240Y/139 VAC? If there's no advantage then the wye is the best option all things considered.
 
LarryFine said:
You don't consider the tap to be a neutral? It's not equal voltage from all lines, but that's not "the" definition of one.
Click to expand...
It is not a neutral because pretty much by definition it has to be the same voltage from line to ground for all lines.

Just like a 2 wire 120 volt system with one leg grounded has no neutral.
 
petersonra said:
It is not a neutral because pretty much by definition it has to be the same voltage from line to ground for all lines.
Click to expand...
I'm not sure I'd agree with that. From Art. 100:

Neutral Conductor. The conductor connected to the neutral
point of a system that is intended to carry current under
normal conditions.

Neutral Point. The common point on a wye-connection in a
polyphase system or midpoint on a single-phase, 3-wire system,
or midpoint of a single-phase portion of a 3-phase delta
system, or a midpoint of a 3-wire, direct-current system.
 
augie47 said:
Not challenging in any way (that would be blasphemy).. just curious, why ??
( I lead a sheltered life ;) never saw a 240/139)
Click to expand...
Just currious do you have 220Y127 in your parts?
Thats more 'standard' in the America's.
240V motors do just fine on that.
 
None of the equipment requires a neutral if that makes a difference.
Each piece of equipment will have four conductors, one for each phase and a ground.
 
Jbyars said:
None of the equipment requires a neutral if that makes a difference.
Each piece of equipment will have four conductors, one for each phase and a ground.
Click to expand...
3 phase hi-leg delta is the most common standard 3 phase 240 setup.
If you have a single phase 240V loads you need '240'V straight rated breakers
220Y127 you could use common plug on breakers 120/240 rated.
Personally I'd go with 240 Hi leg Delta.
 
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