oldsparky52
Senior Member
- Location
- Wilmington, NC USA
208Y buck-boost
- Thread starter FionaZuppa
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kwired
Electron manager
- Location
- NE Nebraska
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- EC
That minor little thing where you placed a red arrow I presume that is almost like having a misspelled word in there.Schneider will be fixing their bad wiring diagram #7 !!
.... maybe. I made them (xfrmer engineer) aware of the issue, so who knows if they'll fix it.
Why you keep focusing on voltages to neutral when you have no neutral connection to your load? As mentioned an open delta configuration will work with a typical three phase motor and only needs two transformer units. The motor only cares about voltage between each input lead as well as phase displacement. Many phase converters are worse off then it comes to that criteria yet are still used.
- Location
- Wisconsin
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- PE (Retired) - Power Systems
You need to stop use the source neutral as your reference point. It is only of concern when the load requires a neutral connection, the transformer does not need it at all, regardless of its connection.
A set of windings, configured in a wye can certainly be connected to a 3 wire feed. In fact the source neutral should almost never be connected to the neutral point of a wye connected primary, unless you are a utility or the transformer is configured wye-wye.
gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
190424-0844 EDT
This thread started off with the simple statement
With this understanding there is no need for balanced voltages from the supplying 3 phase source. Thus, a two transformer boost system can provide the necessary 3 phase delta voltages.
Now we get to the lack of circuit theory becoming a problem. Some had the idea that boost had to come from the 120 legs as input. This would be correct for a 3 transformer boost, but this is a 2 transformer boost from a most installation efficient perspective.
The boost suppliers are not providing useful diagrams for the 2 boost transformer circuit to provide an intuitive vision of the circuit in relation to phasors.
First, there are two separate transformers, not one long winding with various taps.
Second, for the two boost transformer approach the boost primary comes from a line to line source, not a line to neutral.
Third, most boost transformers are wound with an isolated secondary so that a single transformer model can be used for either buck or boost. Drawing diagrams with these distinctions would make it clearer.
Fourth, if the drawings showed the separate transformers at 120 degrees apart visually and related to the 3 phase source, then I believe the reader would more easily understand what the circuit was doing.
If one does not have a true understand how a circuit works, blindly plugs values into an equation, and gets some result, then it is easy to get wrong results.
In general our modern society has been dumbed down to not understand how things work. How many people today can tell you what 12*12 equals, or 11*11, or 2^10, or 6+7, or how a car with stop-start engine control works, etc.
.
This thread started off with the simple statement
Note: it is stated that it is wye wound, but then goes on to say it is 3 wire. Thus, fundamentally it can be viewed as a delta load, and neutral of the source is of no consequence other than voltage levels to earth.
With this understanding there is no need for balanced voltages from the supplying 3 phase source. Thus, a two transformer boost system can provide the necessary 3 phase delta voltages.
Now we get to the lack of circuit theory becoming a problem. Some had the idea that boost had to come from the 120 legs as input. This would be correct for a 3 transformer boost, but this is a 2 transformer boost from a most installation efficient perspective.
The boost suppliers are not providing useful diagrams for the 2 boost transformer circuit to provide an intuitive vision of the circuit in relation to phasors.
First, there are two separate transformers, not one long winding with various taps.
Second, for the two boost transformer approach the boost primary comes from a line to line source, not a line to neutral.
Third, most boost transformers are wound with an isolated secondary so that a single transformer model can be used for either buck or boost. Drawing diagrams with these distinctions would make it clearer.
Fourth, if the drawings showed the separate transformers at 120 degrees apart visually and related to the 3 phase source, then I believe the reader would more easily understand what the circuit was doing.
If one does not have a true understand how a circuit works, blindly plugs values into an equation, and gets some result, then it is easy to get wrong results.
In general our modern society has been dumbed down to not understand how things work. How many people today can tell you what 12*12 equals, or 11*11, or 2^10, or 6+7, or how a car with stop-start engine control works, etc.
.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
The drawings that Square D selector comes up with are same drawings in their printed catalog - they are a connection diagram only and not theory related illustrations. They don't even show any voltages in the diagram, just how to connect it. You already told the selector (or used there selection formulas if doing so out of printed catalog) to establish what units you need and it tells you which connection diagram applies for your situation.
Connection diagram for many things, like the motor OP has may not illustrate much more than connections either. Many 9 lead wye wound motors don't even show the wye point in the connection diagram.
Last edited:
oldsparky52
Senior Member
- Location
- Wilmington, NC USA
Somewhat crude, but this is how I now understand the 2 transformer set up.
(substitute volts for inches)
(substitute volts for inches)
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
Yeah, but I corrected the "wye motor" part in that next post, I called to verify the motor config, they said the motors are delta wound.
As for the other comment about why I keep using N in the cfg, it's because the Schneider buck-boost calulator uses 3 xfrmers when the source is wye, it does not ask what the load type is. The N is needed when using the 3 xfrmers as shown in their diagram. The N does not need to carry over to the load if the load does not need it, but perhaps in the future a 3ph 4wire load will come along
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The two transformers are not connected in any type of wye configuration at all. They are in an open delta.
1. Take your drawing and remove the leg pointing to the left (the one at 0 degrees without a measurement on it). The junction point of the two transformers is common to both the source and the load (lets all this A phase). effectively this connects your source B-phase to the junction between the red and black lines at -120 degrees and your C-phase to the junction between the red and black lines at 120 degrees
2. Change your 120 measurement to be 208.
3. Change your boost voltage to be 27.7 (it is actually 208*32/240) instead of 32
- Location
- Connecticut
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- Engineer
Yeah, but I corrected the "wye motor" part in that next post, I called to verify the motor config, they said the motors are delta wound.
As for the other comment about why I keep using N in the cfg, it's because the Schneider buck-boost calulator uses 3 xfrmers when the source is wye, it does not ask what the load type is. The N is needed when using the 3 xfrmers as shown in their diagram. The N does not need to carry over to the load if the load does not need it, but perhaps in the future a 3ph 4wire load will come along
The Schneider buck boost calculator uses 2 xfmers in an open delta if you only need 3 wires for the load. See post #52.
That is all you need for your application, 2 xfmers.
Why do you need two? Wouldn't one autotransformer do the job?
oldsparky52
Senior Member
- Location
- Wilmington, NC USA
With only one transformer, won't you have an unchanged voltage between the 2 unmodified phases?
oldsparky52
Senior Member
- Location
- Wilmington, NC USA
Thank you Jim (for trying to help me).
I was trying to get in my head the changes that are made to the original configuration to get the new configuration. It's obvious I need to go back to school if I really want to understand, and that ain't happenin
. I think I'll just go back to being retarded, I mean retired.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Only on single phase.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Just as you can have a single core three phase isolation transformer you can have a single core three phase autotransformer (in either wye or delta configuration.)
The delta version would rotate all three absolute phase angles while preserving the 120 degree separation
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
A single-core 3ph transformer is still three transformers. Each phase's primary and secondary windings share one leg of the core, but multiple phases can not share a single leg.
I have used three phase versions. They worked just fine.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
But if someone asked you what a box holding a single core three phase transformer contained, you probably would not answer "three transformers". :angel:
- Occupation
- Licensed Electrician
It doesn't matter how the motors are wired internally, star or delta, and it doesn't matter what the source voltage is, star or delta. The only thing that matters is line to line voltage.
You do not pull a neutral to the transformers. There is no reason to and it may cause problems.As for the other comment about why I keep using N in the cfg, it's because the Schneider buck-boost calulator uses 3 xfrmers when the source is wye, it does not ask what the load type is. The N is needed when using the 3 xfrmers as shown in their diagram. The N does not need to carry over to the load if the load does not need it, but perhaps in the future a 3ph 4wire load will come along
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
No, I would say a three-phase transformer, electrically equivalent to three single-phase transformers.
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