Phase Connection Interchanged in 3 Phase Transformers

[nightfox1925]

I have a Dyn11 3 phase, Negative Polarity, wye-delta transformer connected to a supply with ABC phase sequence. One of my engineers informed me that the same transformer can be easily converted to Dyn5 by simply interchanging the H1 and H2 (phase A and B). He showed me a vector sketch of the Dyn11 and a Vector sketch of a Dyn5 and seems to be the same connection on both primary and secondary if he interchange H1 and H2 of the Dyn11 XFR. I also made a sketch myself and by interchanging the phases, rotated the primary delta vector to point the "new phase A" at top reference and if I convert to wye, I found out that the phase sequence on the wye side is reversed to CBA.

Is my vector sketch correct or his? I am also assuming to relate the same case to an induction motor with delta connected winding that if I interchange the 2 phases, I get reverse rotation due to reversed phase sequence.

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[davidbeach]

Swap two phase on only one side of the transformer and you get a different phase relationship between primary and secondary AND a reversal of phase sequence. Swap two leads on the secondary and you get back to the original phase rotation. Connected as necessary you can get all 6 "odd" connections from 1 to 11. One primary connection gives you 3 of them, 11, 7, and 3 in your case while swapping two phases on the primary and connecting the secondary as needed produces 1, 5, and 9.

 

[nightfox1925]

Thanks dave. What do you mean "while swapping two phases on the primary and connecting the secondary as needed produces 1, 5 and 9"? Do you mean swapping phases on the secondary windings or terminals.

My engineer is refering on swapping phase terminals without opening the transformer. Swapping the primary cable connections that is. Do you mean I can derive Dyn5 from a Dyn transformer by simply swapping cable terminations on both primary and secondary terminals? What cable phase I will interchange on both primary and secondary then? If you can provide me then I will try to re-check the vector skectch myself. Your assistance is highly appreciated.

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[slavag]

Hi Nightfox1925.
Yes, you need only swapp cable termination on both of sides.
See 3 options for swapp:
HV LV
L1 L2 L3 L1 L2 L3
1U 1W 1V 2W1 2V1 2U1
or
1W 1V 1U 2V1 2U1 2W1
or
1V 1U 1W 2U1 2W1 2V1

L1, L2, L3 in ANSI A,B,C : connection to conductors.
Regards.
Slava

 

[slavag]

BTW, If I rememeber right, this type of swapp possible only in DY (DYn) 11 or DY (DYn) 5 xfr.

 

[RalphChristie]

See faq238-1090

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[slavag]

Hi Ralph.
Thank you.
According to you FAQ, my post is wrong or I'm not underastand something.
I know 100%, this type of connection work correctly.
Please correct me.
Regards.
Slava

 

[RalphChristie]

Slava:

The best way to see it is to draw a vector-diagram of any star/delta or delta/star transformer.

Now, on that chosen transformer, change the transformer connections just on one side. By rotating the connections, the vectorgroup is also changing. Thus, by using a Dyn1 connection, rotation on one side will result in either a Dyn5 or a Dyn9 transformer. By rotating the phases, you will not change phase sequence. (for a Dyn11-connection it will result in either a Dyn3 or a Dyn7-connection)

If you put the vector-diagram of a Dyn1 next to a Dyn11, you'll notice that the two is mirror images of each other. Thus, by changing the phase rotation (swapping two phases) on both sides, (From ABC to ACB and abc to acb) you'll change the vector group from a Dyn1 to a Dyn11.

Unfortunately it is difficult to explain without drawings. By checking your first post, it seems as if you haven't change your vector-group at all, the shift between primary and secondary stays the same with every rotation.





nightfox1925:

By changing just on one side of the transformer, you are not going to change a Dyn11 transformer into a Dyn5-connection. The Dyn11 transformer will change either to a Dyn7 or a Dyn3 by changing connections on one side only. To change from a Dyn11 to a Dyn5, you'll have to change connections on both sides of the transformer.
Just a note:

I have a Dyn11 3 phase, Negative Polarity, wye-delta transformer

Although it seems to be not important, remember that Dy is actually Delta-wye and not Wye-delta.
What do you mean by negative polarity?



Remember, a transformer is internally wired to be a certain vector-group. We can change the vector-group by doing unconventional connections external, but internal the transformer remains the same. Thus a Dy11 transformer is wired internally to be a Dy11, and it will stay a Dy11 without any internal changes, but we can change the system (unconventional) such that the transformer behave like either a Dy1, Dy3, Dy5, dy7, Dy9 or Dy11 transformer.

Regards
Ralph

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[slavag]

Hi Ralph.
I'm agree with all your words.
I write my first e-mail after diagrams.
Please see again, in each case I change both of connection
(LV and HV). Now I check again myself, I see it's OK.
Thank you.
Slava

 

[slavag]

Hi Ralph.
Ohhh, I drw vector groups with several options.
Any problem.( some my black-out).
We told about same.
Thank you.
Slava

 

[nightfox1925]

Although it seems to be not important, remember that Dy is actually Delta-wye and not Wye-delta.
What do you mean by negative polarity?

I am placing polarity marks on each transformer winding and I have assumed a negative polarity for reference in drawing the vector diagram for both Delta and Star windings to determine the direction of current flow. What I do is draw the delta and take the delta tip as the reference like a minute hand and the associated hour hand to where the vector falls say for 1 (1 o clock). I assign these arrows marks as "A" (on delta symbol) and "a" (for the wye symbol) corresponding to the minute and hour hand respectively. Then on the wye side I draw the other phases and assign the polarity marks. From this wye symbol with polarity, phase assignment, winding assignment and direction, I derive the equivalent Delta vector.

I will draw the vector diagram with your tips in mind and see the result. I will provide you the details on my next post and attach the scanned sketch.

Thanks for the support.

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[stevenal]

Please see faq238-1154. Although DY1 and DY11 are used in this example, you should be able to adapt the method to DY5.