JFletcher
Senior Member
- Location
- Williamsburg, VA
I thought it was 3 conductors (2 hot + neutral) on the primary side and 4 on the secondary; two phase wires in+ neutral , 3 plus center tapped neutral out. Will try to find a pic.
3 phase 120/208
- Thread starter mannyb
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I thought it was 3 conductors (2 hot + neutral) on the primary side and 4 on the secondary; two phase wires in+ neutral , 3 plus center tapped neutral out. Will try to find a pic.
mivey
Senior Member
They don't. They can use two ungrounded phases and one grounded neutral. An open wye-delta for instance.
mivey
Senior Member
Three conductors on the primary side. The neutral is a conductor. You can't make it happen with only two conductors on the primary side.
add: I replied before your corrected update.
mivey
Senior Member
That is correct. Search for open wye - delta.
jumper
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Mgraw
Senior Member
- Location
- Opelousas, Louisiana
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- Electrician
JFletcher
Senior Member
- Location
- Williamsburg, VA
That's the pic ^ I was looking for. Are the phases still 120* apart with open delta? A to N and N to C are 180* total, correct? Does that make A to B and B to C 90* ea vs 120*, or is the neutral on the split phase on the small pot (A to N to C) splitting one phase in half and the phase angles between A, B, and C all 120* like every other 3 phase application?
jumper
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- 3 Hr 2 Min from Winged Horses
MAC702
Senior Member
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- Clark County, NV
mivey
Senior Member
A is the high leg and AN is 90 degrees from CN and BN. CN and BN are 180 degrees apart exactly like a center-tapped single phase systen.
AB and CA and BC have a 60 degree separation like any normal three phase system, either wye or delta.
The 120 degree separation is not for line to line phases but is for the line to neutral phases when the neutral is at the middle of the wye configuration. You lose that when the neutral move to the center tap position in a delta.
mivey
Senior Member
No. You lose the 120 degree LN relationship in the high-leg delta. The LL phases do maintain the 60 degree separation.
A is the high leg in the posted pic.
JFletcher
Senior Member
- Location
- Williamsburg, VA
Holy sine waves Batman! What the heck did you just ask?
Yeah that was messy! I was basically asking if the phases were 90, 180, 90, or 120, 120, 120, or something else. and I was assuming B was the high leg, not A as in the pic.
and ty for the replies gentlemen, I *think* I understand now.
mivey
Senior Member
The high leg delta is just the normal single-phase center-tapped system with a high-leg phase added.Holy sine waves Batman! What the heck did you just ask?
In fact, the center-tapped portion is metered like a single-phase service and the third leg is metered separatly as a 208 volt single-phase leg. The total metering is a combination of the two single-phase metering stators.
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mivey
Senior Member
90, 180, 90 for LN phases (actually two different phase systems consisting of two 120 volt phases in one system and one 208 volt phase in the other system)
60, 60, 60 for LL phases (three 240 volt phases in one system).
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
The secondary I understood, it was that wye primary that threw me.
Mostly I have dealt with closed/full deltas, the secondary having a center tap, but Delta to Delta.
I just extended that idea to the open delta.
So, when the others brought up a noodle being used on the primary....I am thinking— not on my trannies, you are not!
Did not realize we discussing two different set ups.
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Yes. The latter.
AN and NC are 180 degrees out of phase. You can either call this splitting the AC phase or center tapping the AC phase.
Just do not let the terminology lead you to believe that "splitting" 180 produces 90!
OOPS.
My reply above was based on B being the high leg, which is not the case in the diagram shown. But I think that JFletcher was making the same mistake.
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The lines representing the line-line coils meet at a 60 degree angle. That does not mean that the corresponding phasors are 60 degrees apart!
-60 + 180 = 120.
mivey
Senior Member
The wye primary can cause confusion also. On an open-wye primary you use the neutral but on closed wye you do not. Sometimes this causes linemen to scratch their heads (especially when they are told to include a neutral cutout to ground the neutral when energizing but then open it to float the neutral afterwards).
I found a large closed wye-delta service a while back that had the wye grounded. It was acting as a grounding bank and causing primary protection problems including high ground currents and blown fuses. Had been that way for decades and not noticed. I guess the system unbalanced finally got the better of it. Once the primary neutral was floated, the problems went away. Imagine that.
mivey
Senior Member
That is true.
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
I know little about the POCO side of things for the most part. As I said earlier, I really have only paid attention to the secondary since that is what I deal with.
I would totally be the one scratching my head also. “ Use a noodle on a primary side, huh?”.
The whole wye primary was a bit confusing to me, I have heard of wye-wye, but this wye-delta caught me by surprise. I can understand now for the open delta set up.
For small trannies I have hooked up, it has mostly been delta-wye.
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