# Delta wye connection using 3 small transformers

I am confused from a couple of diagrams I have about how to correctly wire 3 small transformers to form a delta wye connection. The transformers are labeled as
Primary H1 H2, H1 H2, H1 H2
Secondary X2 X1, X2 X1, X2 X1

My question is in all the diagrams I have the Delta connections are identical, but the wye connections in one of the diagrams shows all of X1's tied together to form the neutral and another diagram shows all of X2's tied together to form the neutral. So does it matter whether I use X1's as the hot connections and X2's as the neutral connections or viceversa?
THANKS!

Connecting all X2 together will give 3 phase output.
Connecting all X1 together will give 3 phase output.
There will be a difference of 180 degrees between the 3 phases depending on which connection is used. ?There may be a difference in phase rotation, will have to think about that?
The output voltage will be the same for both connections.
If you are using the output for a rectifier the connection will not make any difference.
If you are using the output for phase control, it may make a difference depending on the circuit you are using.

Is the higher voltage side connected in wye? I would recommend using NEMA standardized connections. The industry practice is that the higher voltage side be labeled so as the line to line voltages on the high voltage side lead those of the low voltage side by 30 degrees electrical phase.

If the high side is in wye, low side in delta, here are the connections:

Y-side: Let us use "H2" as the neutrals. All 3 "H2" terminals are joined. Phase A hot connects to H1 of xfmr A, phase B hot connects to H1 of xfmr B, phase C hot connects to H1 of xfmr C. If this Y-side is a secondary, then it might be desirable to connect the neutral (H2-H2-H2) to earth ground. It depends on the application. If the Y-side is the primary, then an earth ground may already be present. Definitely check if you need to have the neutral grounded.

Delta-side: Connect X2 of xfmr A to X1 of xfmr B. Connect X2 of xfmr B to X1 of xfmr C. Connect X2 of xfmr C to X1 of xfmr A. Then label as follows.

The junction of xfmr A X1 & xfmr C X2 becomes phase A. The junction of xfmr B X1 & xfmr A X2 becomes phase B. The junction of xfmr C X1 & xfmr B X2 becomes phase C.

With these connections & phase labeling, the line to line voltages on the lower voltage delta side will lag those on the higher voltage wye side by 30 degrees, in accordance w/ power industry standard practice in North America. I.e. the A-B line-to-line voltage on the wye side leads the A-B l-l voltage on the delta side by 30 degrees.

If you're using the delta as the high side, let me know & I'll help you, as the designations would be different. Have I helped? Later, I'll attach a sketch.

Claude

Is the higher voltage side connected in wye? I would recommend using NEMA standardized connections. The industry practice is that the higher voltage side be labeled so as the line to line voltages on the high voltage side lead those of the low voltage side by 30 degrees electrical phase.

If the high side is in wye, low side in delta, here are the connections:

Y-side: Let us use "H2" as the neutrals. All 3 "H2" terminals are joined. Phase A hot connects to H1 of xfmr A, phase B hot connects to H1 of xfmr B, phase C hot connects to H1 of xfmr C. If this Y-side is a secondary, then it might be desirable to connect the neutral (H2-H2-H2) to earth ground. It depends on the application. If the Y-side is the primary, then an earth ground may already be present. Definitely check if you need to have the neutral grounded.

Delta-side: Connect X2 of xfmr A to X1 of xfmr B. Connect X2 of xfmr B to X1 of xfmr C. Connect X2 of xfmr C to X1 of xfmr A. Then label as follows.

The junction of xfmr A X1 & xfmr C X2 becomes phase A. The junction of xfmr B X1 & xfmr A X2 becomes phase B. The junction of xfmr C X1 & xfmr B X2 becomes phase C.

With these connections & phase labeling, the line to line voltages on the lower voltage delta side will lag those on the higher voltage wye side by 30 degrees, in accordance w/ power industry standard practice in North America. I.e. the A-B line-to-line voltage on the wye side leads the A-B l-l voltage on the delta side by 30 degrees.

If you're using the delta as the high side, let me know & I'll help you, as the designations would be different. Have I helped? Later, I'll attach a sketch.

Claude

Yes, Delta Primary Side and Wye Secondary Side. High/Low. Thanks!

The attached pdf details how to obtain the industry standard high voltage side 30 degree phase lead using a wye-delta as well as a delta-wye xfmr configuration. I added polarity dots to the schematics as a visual aid. This should be what you are looking for. Hopefully it is legible.

Claude

#### Attachments

• abraham_y_delta_phase_conn.pdf
64.1 KB · Views: 144
The attached pdf details how to obtain the industry standard high voltage side 30 degree phase lead using a wye-delta as well as a delta-wye xfmr configuration. I added polarity dots to the schematics as a visual aid. This should be what you are looking for. Hopefully it is legible.

Claude

Thanks So Much! Sauce