Three phase transformer phase angle and group

[Guineafowl]

TL;DR

Can someone please explain the phase angle and group of these two Dy transformer diagrams?

On behalf of someone on another forum; In both cases, he’s been given the answer, but doesn’t understand it:

To me, the group does make sense in both cases, if you imagine the diagrams rotating anticlockwise: the vector X1 lags by 30° in the first case, giving 11 o’clock as the group, and leads by 30° in the second, giving 1 o’clock.

I’m stumped by the phase, as he is. I think it might be to do with the fact that the top delta is clockwise, and the bottom the opposite.

Original thread: https://www.mig-welding.co.uk/forum...ransformer-phase-displacement-symbols.148438/

 

[Gavran]

View attachment 370430

This is group 1. If H1 points at 12 o'clock, X1 will point at 1 o'clock.

View attachment 370431

This is group 11. If H1 points at 12 o'clock, X1 will point at 11 o'clock.

 

[Guineafowl]

Thanks, so by that definition the group 1 will be a 30°, and the group 11 a 330°?

There were two other examples:

I make these group 7 and 11 respectively, so I were all four examples wrong?

The only other point is, for the two examples above, the vector X1 is pointing at the non-dot end of W4 in the first, and at the dot end in the second. Is that a mistake too?

 

[Gavran]

Thanks, so by that definition the group 1 will be a 30°, and the group 11 a 330°?

Yes, you are right. That means X₁ lags H₁ by 30° in group 1, and X₁ lags H₁ by 330° in group 11.

The only other point is, for the two examples above, the vector X1 is pointing at the non-dot end of W4 in the first, and at the dot end in the second. Is that a mistake too?

Both examples are correct. See Figure 4 - D₇ from https://cdn.prod.website-files.com/.../5e37131bc62330e7ed1cedb0_3phXfmrs_GATech.pdf (page 7).

 

[Guineafowl]

Both examples are correct. See Figure 4 - D7 from https://cdn.prod.website-files.com/.../5e37131bc62330e7ed1cedb0_3phXfmrs_GATech.pdf (page 7).

So, what would lead you to point the X1 vector at the dot or non-dot end? It seems arbitrary.

 

[Gavran]

So, what would lead you to point the X1 vector at the dot or non-dot end? It seems arbitrary.

It depends on how X₁, X₂, and X₃ are interconnected with W₄, W₅, and W₆. See again Figure 4-D₇ (the third image on the right).

 

[Guineafowl]

It depends on how X₁, X₂, and X₃ are interconnected with W₄, W₅, and W₆. See again Figure 4-D₇ (the third image on the right).

Ok, there must be some rule I’m missing, after which the penny will drop. Forgive my stupidity.

How is the X1 (or U) junction defined? Put another way, if you had a delta-connected transformer side open in front of you, which one is the first winding, and which is the X1 or U connection? In that figure 4, U is connected to a different winding end in almost every case.