Dyn5 Transformer

[alansam]

I am an electrical engineer in an electro mechanical contracting company.For one of our new projects,our scope included supply and installation of dedicated distribution transformer(1000 kva,11kv/415 v) along with ring main unit and feeder pillar.I was asked to get quotations from suppliers and analyse technical details of those.Here we normally use Dyn11 vector group transformers.However,one of the suppliers had quoted for Dyn5 vector group and its price was less than all the others I had got.I'm confused as to whether it is technically correct to use a Dyn5 group.

1.Also I when I'm connecting the transformer to the supply am I paralleling the transformer to other Dyn11 transformers in the grid?Here the delta side is connected to hv and lv side to load with neutral grounded.I'm asking this because i had read in an article that it is not correct to parallel transformers of different vector groups and I think I'm not paralleling this transformer when connecting to supply.

Please clarify on the above points.

Thanks & Regards,

Alan

 

[templdl]

I am an electrical engineer in an electro mechanical contracting company.For one of our new projects,our scope included supply and installation of dedicated distribution transformer(1000 kva,11kv/415 v) along with ring main unit and feeder pillar.I was asked to get quotations from suppliers and analyse technical details of those.Here we normally use Dyn11 vector group transformers.However,one of the suppliers had quoted for Dyn5 vector group and its price was less than all the others I had got.I'm confused as to whether it is technically correct to use a Dyn5 group.

1.Also I when I'm connecting the transformer to the supply am I paralleling the transformer to other Dyn11 transformers in the grid?Here the delta side is connected to hv and lv side to load with neutral grounded.I'm asking this because i had read in an article that it is not correct to parallel transformers of different vector groups and I think I'm not paralleling this transformer when connecting to supply.

Please clarify on the above points.

Thanks & Regards,

Alan

The diffence between a DYN5 and a DYN11 is that the DYN11's secondary windings are connected such that the X0 ties the start windings together to form the wye where the DYN5 connects the finish windings to form the wye. The DYN11 (Digit 11) provides a 330? lagging or 30? leading (LV leads HV with 30?)
Digit 5 provides a 150? lagging (LV lags HV with 150?).
The difference in output between the Dyn11 and Dny5 and is therefore 180 degrees.

With regards to theory, there are no special advantages of Dyn11 over Dyn5.
In Isolation Application: In isolated applications there is no advantage or disadvantage by using Dy5 or Dy11. If however we wish to interconnect the secondary sides of different Dny transformers, we must have compatible transformers, and that can be achieved if you have a Dyn11 among a group of Dyn5′s and vice versa.
In Parallel Connection: Practically, the relative places of the phases remain same in Dyn11 compared to Dyn5.

 

[wirenut1980]

Templdl,

How can you connect transformers in parallel that have secondaries 180 degrees out of phase? Are you saying that if you have several DYN5's and add one DYN11, then that will work ok?

 

[mivey]

Templdl,

How can you connect transformers in parallel that have secondaries 180 degrees out of phase? Are you saying that if you have several DYN5's and add one DYN11, then that will work ok?

You swap the secondary leads, like you do when you mix additive and subtractive transformers.

 

[wirenut1980]

You swap the secondary leads, like you do when you mix additive and subtractive transformers.

Ah, thank you. So one would have to swap leads on both transformers, right? Because changing them on just one transformer would get you only 120 degrees.

 

[mivey]

Ah, thank you. So one would have to swap leads on both transformers, right? Because changing them on just one transformer would get you only 120 degrees.

If you think of single-phase transformers, one transformer set is at 0?, the other set is at 180?. You only swap one set so they are both 0? or both 180?.

For a three-phase transformer, you will have to swap the primary leads on one of them since the secondary bushings may not be re-configurable. Same end result.

 

[david luchini]

Ah, thank you. So one would have to swap leads on both transformers, right? Because changing them on just one transformer would get you only 120 degrees.

If you think of single-phase transformers, one transformer set is at 0?, the other set is at 180?. You only swap one set so they are both 0? or both 180?.

For a three-phase transformer, you will have to swap the primary leads on one of them since the secondary bushings may not be re-configurable. Same end result.

I would think to connect a DY5 with a DY11 transformer, you'd need to swap a lead on the primary AND secondary of the new transformer to get the same output configuration.

For instance, if a Dy11 is connected ABC (H1-H2-H3) and ABC (X1-X2-X3), to give the secondary a 30? lead, (lets say primary is Vab=480<0, Vbc=480<-120 and Vca=480<-240, and and the secondary Vab=208<30, Vbc=208<-90, Vca=208<-210). If I connect the Dy5 as BAC (H1-H2-H3) and ACB (X1-X2-X3) then I should get the same secondary voltages (Vab=208<30, Vbc=208<-90, Vca=208<-210.)

 

[iceworm]

Not sure where this came from.

View attachment Dyn5.pdf

View attachment dyn11.pdf

 

[david luchini]

Not sure where this came from.

View attachment 8176

View attachment 8177

The vector diagram on the dy5 is incorrect. It doesn't show a -150 degree shift. On the secondary diagram, c1 should be b1, a1 should be c1, and b1 should be a1 to show the proper relationship.

 

[iceworm]

The vector diagram on the dy5 is incorrect. It doesn't show a -150 degree shift. On the secondary diagram, c1 should be b1, a1 should be c1, and b1 should be a1 to show the proper relationship.

It didn't look right to me either - but not my area of expertise.

You want to rotate the Y vector diagram CCW 1/3 turn?

I was thinking rotate the shown Y vector CW 1/3 turn

Aaarrrrgggggg - i don't know.

 

[mivey]

I would think to connect a DY5 with a DY11 transformer, you'd need to swap a lead on the primary AND secondary of the new transformer to get the same output configuration.

No, just one side or the other. Swapping both primary and secondary reverses the polarity then reverses it back and you won't match the other transformer.

For Dy11:

Primary line-ground:
VA: 120.0<210.0?
VB: 120.0<90.0?
VC: 120.0<-30.0?

Primary line-line:
VAC: 207.8<180.0?
VBA: 207.8<60.0?
VCB: 207.8<-60.0?

Secondary line-ground:
Va: 120.0<180.0?
Vb: 120.0<60.0?
Vc: 120.0<-60.0?

Shift: <-30.0?



For Dy5:

Primary line-ground:
VA: 120.0<210.0?
VB: 120.0<90.0?
VC: 120.0<-30.0?

Primary line-line:
VAC: 207.8<180.0?
VBA: 207.8<60.0?
VCB: 207.8<-60.0?

Secondary line-ground (note polarity difference from primary to secondary):
Va: 120.0<0.0?
Vb: 120.0<-120.0?
Vc: 120.0<-240.0?

Shift: <-210.0?



For Dy5 with swapped leads:

Primary line-ground:
VA: 120.0<210.0?
VB: 120.0<90.0?
VC: 120.0<-30.0?

Primary line-line (with leads swapped):
VCA: 207.8<0.0?
VAB: 207.8<-120.0?
VBC: 207.8<120.0?

Secondary line-ground (note polarity difference from primary to secondary):
Va: 120.0<-180.0?
Vb: 120.0<60.0?
Vc: 120.0<-60.0?

Shift: <-30.0?

Note that swapping the leads on one side made the secondary of the Dy5 & Dy11 match.

 

[david luchini]

You want to rotate the Y vector diagram CCW 1/3 turn?

I was thinking rotate the shown Y vector CW 1/3 turn

I'm suggesting a CW rotation. Or relabel c1 as b1, etc.

 

[david luchini]

No, just one side or the other. Swapping both primary and secondary reverses the polarity then reverses it back and you won't match the other transformer.

For Dy11:

Primary line-ground:
VA: 120.0<210.0?
VB: 120.0<90.0?
VC: 120.0<-30.0?

Primary line-line:
VAC: 207.8<180.0?
VBA: 207.8<60.0?
VCB: 207.8<-60.0?

Secondary line-ground:
Va: 120.0<180.0?
Vb: 120.0<60.0?
Vc: 120.0<-60.0?

Shift: <-30.0?

These numbers are incorrect. You are describing a DY1 transformer, not a DY11. With your primary voltages, a DY11 will provide Va=120<240, Vb=120<120, Vc=120<0. This is a positive 30? shift, not a negative 30? shift.

For Dy5:

Primary line-ground:
VA: 120.0<210.0?
VB: 120.0<90.0?
VC: 120.0<-30.0?

Primary line-line:
VAC: 207.8<180.0?
VBA: 207.8<60.0?
VCB: 207.8<-60.0?

Secondary line-ground (note polarity difference from primary to secondary):
Va: 120.0<0.0?
Vb: 120.0<-120.0?
Vc: 120.0<-240.0?

Shift: <-210.0?

These numbers are likewise incorrect for a DY5. A DY5 would have a -150? degree shift. You have described a DY7. But since a DY1 & DY7 are 180? apart just like a DY5 and DY11, let's continue to swapping leads.

For Dy5 with swapped leads:

Primary line-ground:
VA: 120.0<210.0?
VB: 120.0<90.0?
VC: 120.0<-30.0?

Primary line-line (with leads swapped):
VCA: 207.8<0.0?
VAB: 207.8<-120.0?
VBC: 207.8<120.0?

Secondary line-ground (note polarity difference from primary to secondary):
Va: 120.0<-180.0?
Vb: 120.0<60.0?
Vc: 120.0<-60.0?

Shift: <-30.0?

Note that swapping the leads on one side made the secondary of the Dy5 & Dy11 match.

I don't see that you've swapped any leads. You've just reversed the polarity of your EACH of your inputs. But to reverse polarity on your first winding, you must switch two of your leads (ie, switch A with C and leave B.)

For instance, in your unswapped DY5 (actually DY7,) your first winding is connected A-C, the second winding is connected B-A, and the third winding is connected C-B. Now for your swapped leads DY5, you connect the first winding from C-A (you swapped A and C leads) this would make your second winding connected to B-C (not A-B) and your third winding connected to A-B (not B-C). This would give you secondary voltages of:

Va: 120.0<180.0?
Vb: 120.0<-60.0?
Vc: 120.0<60.0?

You can see that by switching the primary leads, I've got the correct angle to match Va, but that I've reversed the phase sequence to ACB. Swapping B and C on the secondary will give me the correct relationship.

 

[wirenut1980]

These numbers are incorrect. You are describing a DY1 transformer, not a DY11. With your primary voltages, a DY11 will provide Va=120<240, Vb=120<120, Vc=120<0. This is a positive 30? shift, not a negative 30? shift.



These numbers are likewise incorrect for a DY5. A DY5 would have a -150? degree shift. You have described a DY7. But since a DY1 & DY7 are 180? apart just like a DY5 and DY11, let's continue to swapping leads.



I don't see that you've swapped any leads. You've just reversed the polarity of your EACH of your inputs. But to reverse polarity on your first winding, you must switch two of your leads (ie, switch A with C and leave B.)

For instance, in your unswapped DY5 (actually DY7,) your first winding is connected A-C, the second winding is connected B-A, and the third winding is connected C-B. Now for your swapped leads DY5, you connect the first winding from C-A (you swapped A and C leads) this would make your second winding connected to B-C (not A-B) and your third winding connected to A-B (not B-C). This would give you secondary voltages of:

Va: 120.0<180.0?
Vb: 120.0<-60.0?
Vc: 120.0<60.0?

You can see that by switching the primary leads, I've got the correct angle to match Va, but that I've reversed the phase sequence to ACB. Swapping B and C on the secondary will give me the correct relationship.

I agree, after drawing it out I was unsure how one would reverse the polarity of every primary vector out in the field. One other question, is it common practice when drawing a vector from Va to Vb (where the arrow head is at Vb and the arrow tail is at Va), to write it as Vab, or Vba?

Mivey, I see you writing it as Vba, but I always have thought of it as Vab. Could just be a personal preference, but if I am doing it wrong, then I need to change it.

 

[david luchini]

I agree, after drawing it out I was unsure how one would reverse the polarity of every primary vector out in the field. One other question, is it common practice when drawing a vector from Va to Vb (where the arrow head is at Vb and the arrow tail is at Va), to write it as Vab, or Vba?

Mivey, I see you writing it as Vba, but I always have thought of it as Vab. Could just be a personal preference, but if I am doing it wrong, then I need to change it.

You would call the vector from A to B (head at B) Vab. You would call the vector from B to A (head at A) Vba. Vab and Vba will have an angle 180? apart. Mivey used both Vab and Vba in his examples.

 

[mivey]

These numbers are incorrect. You are describing a DY1 transformer, not a DY11.

You are correct. I had it backwards.

Swapping B and C on the secondary will give me the correct relationship.

Correct again, it requires a swap on the primary and secondary like you said. I completely messed it up by thinking of a single phase transformer with additive vs subtractive polarity. I should have sketched it out instead of punching away on my calculator.

 

[mivey]

One other question, is it common practice when drawing a vector from Va to Vb (where the arrow head is at Vb and the arrow tail is at Va), to write it as Vab, or Vba?

Mivey, I see you writing it as Vba, but I always have thought of it as Vab. Could just be a personal preference, but if I am doing it wrong, then I need to change it.

Vba = Vb - Va (actually Vbn - Van with n as the reference). In this case the voltage at 'a' is the reference and is at the tail of Vba and the voltage at 'b' is at the head of Vba. This is the correct notation since voltage is a difference quantity. Vba is the voltage at 'b' relative to the voltage at 'a'. It is also correct to think of Vba as the voltage drop from b to a.

You could consider voltage rises and that would give you the opposite convention however the most common convention is to consider voltage drops.

FWIW, current is a through quantity. Iba means the current directed from b to a.

 

[mivey]

You would call the vector from A to B (head at B) Vab. You would call the vector from B to A (head at A) Vba.

That is the voltage rise convention. Voltage drops are the more common convention.

Mivey used both Vab and Vba in his examples.

As messed up as it was. But they were voltage drops.

 

[mivey]

Vba = Vb - Va (actually Vbn - Van with n as the reference). In this case the voltage at 'a' is the reference and is at the tail of Vba and the voltage at 'b' is at the head of Vba. This is the correct notation since voltage is a difference quantity. Vba is the voltage at 'b' relative to the voltage at 'a'. It is also correct to think of Vba as the voltage drop from b to a.

You could consider voltage rises and that would give you the opposite convention however the most common convention is to consider voltage drops.

FWIW, current is a through quantity. Iba means the current directed from b to a.

Also see this thread: http://forums.mikeholt.com/showthread.php?t=143008

Another reference is the classic T&D book from Westinghouse and it has:

Also, the inclusion of reference-direction arrows on the diagram, even when the double-subscript system is used, may aid in writing equations, although they are not strictly required. If used, they must be consistent with the double-subscript system. That is, each arrow must be directed from the second subscript toward the first for voltages, and from the first subscript toward the second for currents.

Most of my engineering and electrical references also follow this convention.