Wye or Star vs the Delta Electrical System

david luchini

Moderator
Staff member
Location
Connecticut
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Engineer
My bad should have been 120+120 equals 208, not 240

I did all ready.

Thanks :)
I still don't follow your logic.

A simple explanation though would be is that two of the 120 volt voltage windings are in series and additive producing 208, but at the same time the other 120 volt winding is subractive which results in 208 volts.
If the 2 120v windings are additive to equal 208V, then nothing needs to be "subtractive" to get a result of 208V. The "other" 120v winding plays no part in additive voltage of the first 2 windings.
 

ronaldrc

Senior Member
Location
Tennessee
I think that lots of people have wondered about the why of the square root of 3 in three phase systems. The particular issue of the 'missing' 32V came up in a discussion several years ago, about the 'oregon fudge factor'.



Here I disagree with you.

I specifically brought up power factor and showed an extreme case where something is lost by having two coils, not in phase, feed a single phase load. What is lost _must_ be understood in terms of the power factor of the loads on the individual coils. And I absolutely agree: if you connect a single phase load to two legs of a wye system, because of the power factor seen by the individual coils, the equipment will need to have larger VA capability than if the coils were in phase.

But once you understand that this 'loss of capability' is created by power factor in the individual coils, you will see two other important points:

1) You see the exact same loss of capacity in a delta system. In a delta system the output voltage is the coil voltage, so no voltage is 'lost'. But add up the _currents_ in the various coils. You will see the exact same percentage loss of total current versus coil currents. In a wye system the voltage is lower than the sum of the individual coil voltages, but terminal current equals coil current. In a delta system the voltage is the coil voltage, but the terminal current is less than the sum of the coil currents. (In both cases the 'deficit' is explained using a vector sum.)

2) If, rather than considering single phase loading, you consider three phase loading, when you have a balanced three phase load then nothing is lost, and the power factors in the coils is the same as the power factor of the load. With a balanced three phase load a balanced three phase source doesn't create any additional 'coil power factors'.

-Jon

Thanks for a good logical response which makes perfect sense, in other word because of circulating currents
in the Delta system it is just as inefficient as the Wye system.So they are more or less equal.


Thanks Ronald :)
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
No , but I do think if 120+120 =208 instead of 240 something is wrong.
No offense intended, but it is your thinking that is wrong. You cannot just add AC voltages like you can DC voltages without taking phase angles (i.e. timing) into consideration. There is no "lost voltage". Power engineers are extremely, one might say painfully, aware of the physics of power transfer. Given your apparent lack of understanding (again, no offense intended) of how such things work, do you seriously think that you have stumbled onto something that they have overlooked?
 

Besoeker

Senior Member
Location
UK
No offense intended, but it is your thinking that is wrong. You cannot just add AC voltages like you can DC voltages without taking phase angles (i.e. timing) into consideration. There is no "lost voltage". Power engineers are extremely, one might say painfully, aware of the physics of power transfer. Given your apparent lack of understanding (again, no offense intended) of how such things work, do you seriously think that you have stumbled onto something that they have overlooked?
You can take a horse to water..........
 

junkhound

Senior Member
Location
Renton, WA
Try this analogy for the vector challenged folks, an analogy that has been helpful to others.

You have a spring scale at the 6:00 o'clock position attached to a plow tied to a stump with 2 ropes attached.

You and a buddy stand side by side at the 12:00 o'clock position and pull with 120 pounds on the ropes, the scale reads 240 pounds.

Now, you go to and your buddy to 10AM and 2PM positions and both pull again with 120 pounds force. Due to the vectors, the scale reads only 208 pounds. Where is the other 32 pounds combined - you and your buddy are pulling on each other sideways.

No work done yet, just force applied.

Now you untie the plow from the stump and both pull on the rope from the 12 o'clock position, and 240 pounds pulls the plow thru the ground at a certain speed (aka current) producing work. If you go to the 10 and 2 o'clock positions, you cannot pull the plow as fast but you do end up walking in parallel lines because you are pulling against each other (but doing no work on each other as you are not moving relative to each other), The plow is not going as fast and you are pulling less force going into pulling the plow, (aka lower current * volts, less work), so the total work being done is less.

To realize the vectors in how you think you are still pulling 120 pounds but really are not, attach a pole from the 10 to 2 o'clock positions. This pole now can provide the force between you and your buddy (e.g. 32 pounds), so now, parallel to each other you are only pulling 104 pounds in line with the direction the plow is going rather than 120 pounds in line with the ropes. You let the pole take the sideways static 32 lb. force, and you are each contributing 104 pounds to pulling the plow.

re: in other word because of circulating currents in the Delta system it is just as inefficient as the Wye system.
Hoo boy, do we want to get into a discussion of triplett harmonics and delta - Y transformers -- other than that, the italic statement is false.
If one had a transformer with superconducting wire and no hysterysis or eddy current core losses, both delta and Y transformers would be 100% efficient.
The phrase "just as inefficient as the Wye system" indicates there are still basic misunderstandings of how transformers work. Very hard to do on-line as some basics such a phase vectors, etc. are missing in OP's knowledge base - hopefully the rope analogy above can help with that?
 
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kwired

Electron manager
Location
NE Nebraska
Ron, voltage alone is not power, I think you know that. Just because the voltage is lower doesn't mean anything has been lost.

Take what others have recently mentioned and then add this to your data banks:

There is a possible difference of 240 volts (RMS) difference but because the two phases are 120 degrees apart, they are never at peak difference at the same time (this is kind of what the phase angle and multiphase systems is all about), but the wave of each is changing at same rate so they are always at the same differential. If the phase angle is 180 degrees, they are always at peak differential.

Does that help?
 

ronaldrc

Senior Member
Location
Tennessee
Ron, voltage alone is not power, I think you know that. Just because the voltage is lower doesn't mean anything has been lost.

Take what others have recently mentioned and then add this to your data banks:

There is a possible difference of 240 volts (RMS) difference but because the two phases are 120 degrees apart, they are never at peak difference at the same time (this is kind of what the phase angle and multiphase systems is all about), but the wave of each is changing at same rate so they are always at the same differential. If the phase angle is 180 degrees, they are always at peak differential.

Does that help?
I never have said that voltage alone is power. Your statement about what phase angle is,Well the Engineers on here can't even agree on what a Phase is ,let alone multiphases. One on here says a single phase is more than one phase . The same one calls a three phase wye with a center tap on each winding 6 phase.

I shouldn't have ever mentioned Neg. PF it really got the Engineers stired up.

Although there are great Electrical Engineers out there ,they evidently don't post on forums. I have really lost all my respect for Electrical Engineers since I have been on the Internet.

All they do is try to put Electricians down when they ask a simple question.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
Try answering these :
given: One bag of corn weighs 240lbs and One barrel of water weighs 208lbs.

Which container is more efficient?
What happened to the missing 32lbs?

You can build a 240Y or a 208Y system, there is still a 32 volt difference. Is one more efficient than the other?
PF and phasor angles mean nothing.
 

GoldDigger

Moderator
Staff member
One on here says a single phase is more than one phase . The same one calls a three phase wye with a center tap on each winding 6 phase.

I shouldn't have ever mentioned Neg. PF it really got the Engineers stired up.
He has a point. What you call a wye with each winding center tapped is not a wye.
If it were a wye you would have two concentric triangles of line wires, one at 120 volts to neutral and one at 240 volts to neutral.

If instead you connect ONLY the three center taps together you have two wyes with a phase offset or one hexagon of phase terminals.
Just as a 120-0-120 is called a single phase, you could also call the double wye only three phase. But for feeding a rectifier bank it will provide twice as many charging pulses per cycle, giving the performance of six phases.

And I do believe that there are some very good EEs on this Forum. :)


Sent from my XT1080 using Tapatalk
 

junkhound

Senior Member
Location
Renton, WA
Try answering these :
given: One bag of corn weighs 240lbs and One barrel of water weighs 208lbs.

Which container is more efficient?
What happened to the missing 32lbs?

You can build a 240Y or a 208Y system, there is still a 32 volt difference. Is one more efficient than the other?
PF and phasor angles mean nothing.
Well, mix'em together, boil, cover, a few days or weeks later boil at 80C or so thru a Cu coil, drink the 32# and be happy <G>
During and after drinking that there 32#, ya aint gonna be very efficient for quite awhile either.
 
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kwired

Electron manager
Location
NE Nebraska
I never have said that voltage alone is power. Your statement about what phase angle is,Well the Engineers on here can't even agree on what a Phase is ,let alone multiphases. One on here says a single phase is more than one phase . The same one calls a three phase wye with a center tap on each winding 6 phase.

I shouldn't have ever mentioned Neg. PF it really got the Engineers stired up.

Although there are great Electrical Engineers out there ,they evidently don't post on forums. I have really lost all my respect for Electrical Engineers since I have been on the Internet.

All they do is try to put Electricians down when they ask a simple question.
You have a point about the engineers not being able to agree on what a phase is, though they actually do agree more consistently on what two phase or three phase is.

I've just been trying hard to convince you that just because the voltage of one system is 32 volts lower than another system doesn't mean anything has been lost.

Say you have a 240 volt delta system and compare to a 480 volt wye system. Did you lose something in the 240 volt system that you had in the wye system? Until you factor in the current that can be produced there is nothing to gain or lose, all you have is a system of different voltage.

How about a 480 volt delta compared to a 480 volt wye system? Here is where you would be comparing apples to apples but they both have to be same KVA capacity also before you can truly determine if one would have more inefficiencies than the other, and those inefficiencies would be wasted energy from the core and coil, a drop in voltage alone is not an inefficiency, the heat given up because we have resistance (which will cause the drop in voltage, and is caused because we have current) is an inefficiency.
 

Besoeker

Senior Member
Location
UK
I never have said that voltage alone is power. Your statement about what phase angle is,Well the Engineers on here can't even agree on what a Phase is ,let alone multiphases. One on here says a single phase is more than one phase . The same one calls a three phase wye with a center tap on each winding 6 phase.
Do I sense a tiny bit of negativity?
I believe I called it hexaphase. You might care to google that.

I presented this arrangement:



It shows the displacement of each of the six phases.

And here's one we made earlier:

 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I never have said that voltage alone is power. Your statement about what phase angle is,Well the Engineers on here can't even agree on what a Phase is ,let alone multiphases. One on here says a single phase is more than one phase . The same one calls a three phase wye with a center tap on each winding 6 phase.

I shouldn't have ever mentioned Neg. PF it really got the Engineers stired up.

Although there are great Electrical Engineers out there ,they evidently don't post on forums. I have really lost all my respect for Electrical Engineers since I have been on the Internet.

All they do is try to put Electricians down when they ask a simple question.
Please be careful with your stereotyping. I apologize if anything I said was interpreted by you as a putdown; such was not my intent. I deal with electricians all the time and I have learned a great deal about code issues from them. When one of them is harboring a misconception due to a lack of understanding of the fundamentals, I try to enlighten them, not put them down.
 
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ronaldrc

Senior Member
Location
Tennessee
Please be careful with your stereotyping. I apologize if anything I said was interpreted by you as a putdown; such was not my intent. I deal with electricians all the time and I have learned a great deal about code issues from them. When one of them is harboring a misconception due to a lack of understanding of the fundamentals, I try to enlighten them, not put them down.

I do owe you an apology you don't and no one else on here owes me one. I'm just old and not getting any younger.

I went through this very misconception about 7 or 8 years ago on this very subject. Arguing almost the same issue.
And one of the members set me straight I don't remember if it was Rattus or Larry Fine but I believe it was one of them, I don't know why I didn't remember that but it just donged on me this morning.


I can not for some reason get it through my thick skull that A phase and the following phase don't get their peak voltage at the same time. You all tried to make it clear that it follows 120 degrees later.

I am wrong as you all know the two 120 volt windings should not add to 240, dag that Crowe taste worse
every time I have to eat it. There is no 32 volts difference.

I will apology to the Engineers I put down, most people don't agree on everything but thats just human nature.

Ronald :)
 
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kwired

Electron manager
Location
NE Nebraska
I will not apologize for the comment that the engineers can not agree on what a phase is, somewhere there is a very long thread on that topic that in a way really went nowhere on the topic, why should I apologize for stating something that did happen?

If I did say something that was aimed at a specific individual, I do apologize for that, but I don't think I did. I can put down engineers in general as easily as I can put down contractors or installers and don't feel too guilty of anything, sometimes humor is pointing out your own faults, sometimes you do learn from such things also.
 

kwired

Electron manager
Location
NE Nebraska
Just for you:

Ron look at that graph, start with the 90 degree point, the red phase at a peak is near +600 volts. The voltage at that point in time to both the black and blue phases,which are near - 300 volts, and not at the opposing peak would be in the neighborhood of 900 volts. Of course the RMS voltage is probably (since it was posted by someone from Europe) probably near 415 volts - this just based on relatively simple observation of the graph and not doing any absolute calculations.

Now consider that at the 90 degree point the red is at a peak and the other two phases are equal but not at a peak, this is where you are seeing the apparent loss of 32 volts in the 208 volt system. But you could have a wye system that has a few more turns in the windings to get 240 volts, the wave forms would look exactly the same, but the peak voltages would be just enough higher to give the 240 volts RMS instead of 208.

Unlike a single phase wave you have two other voltage waves you have to compare to at any given instant to determine the voltage between two output conductors, and the voltage from a to b is not always the same at the same instant as it is from a to c, and so forth, but as long as we have a steady sinuous wave the RMS will remain steady.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I do owe you an apology you don't and no one else on here owes me one. I'm just old and not getting any younger.
Hey, no problem. I'm no spring chicken myself and I can be as curmudgeonly as the next guy. :D
 
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