×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

3 Phase DYn1 transformer. Can it be connected externally DYn3 ?

3 Phase DYn1 transformer. Can it be connected externally DYn3 ?

3 Phase DYn1 transformer. Can it be connected externally DYn3 ?

(OP)
3 Phase Delta-Wye DYn1 transformer has primary terminal H1 connected to cable A, H2 to cable B, and H3 to cable C. The secondary terminal X1 is connected to cable a, X2 to b, X3 to c and X0 to cable n. The phase rotation is ABC on secondary.
What external connection changes, on either primary/secondary or both, will make this transformer DYn3, keeping the same phase rotation on secondary?
Thanks.

RE: 3 Phase DYn1 transformer. Can it be connected externally DYn3 ?

You'll have to swap two H connections and two X connections. There are at least 3 combinations that will get you what you need. I'll let you have a bit of transformer vector fun; then pick the one that causes the least trouble when reconnecting.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

RE: 3 Phase DYn1 transformer. Can it be connected externally DYn3 ?

(OP)
Thanks Davidbeach. Vector realignment is a complex subject for me, especially when I have to swap terminals, but I will certainly try.
Meanwhile it seems that I made a mistake in stating the problem. I am describing below more accurately.
We have a 3 phase, 26.4 kV incoming from utility in the substation. There is a Dd0 transformer stepping 26kV down to 480 volt. Another DYn1 transformer 150KVA, steps down 480 volt to 120/208 volt for lighting/heating etc. This 120/208 supply is given to 3 pole Auto Transfer Switch, neutral being common with other incoming supply to ATS. The other low voltage supply of 3 phase 4 wire 120/208 volt, is coming to ATS from utility.
Let us say that ATS's first (Normal) supply, which is internally generated in the substation, is A, B, C and N.
The ATS's second (Emergency) supply is coming from utility, is A', B', and C' and N'. The N and N' go to common neutral bar of ATS.
I measured voltages to check if the 2 sources in ATS are in sync. They are not. The voltage measured are A-A' = 120 volt, A-B' = 240 volt and A-C' = 120 volt. (Similarly for B and C phases.) So there is a phase difference of 60 degree between the two sources in the ATS. Both sources have correct phasor rotation. Obviously, We cannot do anything to the 120/208 volt coming from utility.
I wonder if our DYn1 transformer can be externally rewired as DYn3, (which gives additional 60 degree shift) and in that case, will it bring both sources in sync in the ATS ? Thanks.

RE: 3 Phase DYn1 transformer. Can it be connected externally DYn3 ?

Any delta-wye transformer can be connected to provide a phase shift equal to any odd multiple of 30 degrees.

The one time I had to put that into practice the actual set of swaps was determined by swap that worked at the vertical dead end a span away from the horizontal dead end over the transformer. Once that was determined there was one swap of low-side cables that completed the desired phase shift.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

RE: 3 Phase DYn1 transformer. Can it be connected externally DYn3 ?

You would have to disconnect all 3 coils at neutral ends. At this power, these should be welded.

RE: 3 Phase DYn1 transformer. Can it be connected externally DYn3 ?

No. All done external to the transformer. Draw up a Dy transformer, the terminals are H1, H2, H3 and X0, X1, X2, X3. Assign A to H1 and a to X1, B to H2 and b to X2, and C to H3 and c to X3. Work out the vector relationship of ABC to abc. Now swap things around so that you have B-H1, A-H2, C-H3, b-X1, a-X2, and c-X3. Once again, work out the vector relationship of ABC to abc. It's different and it's some odd multiple of 60 degrees different.

As a hint, there's a FAQ for this forum that describes the "conversion" between Dy1 and Dy11, also a 60 degree shift. That doesn't require any changes inside the transformer either.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

RE: 3 Phase DYn1 transformer. Can it be connected externally DYn3 ?

(OP)
Davidbeach, Thank you.
I was able to draw vectors and understand at least one cable reconnection configuration, which will give 60 degree shift. I did not attempt the other 2 combinations. But now I am convinced that it can be done and there are more than 1 ways to reconnect cables on primary and secondary to get the 60 degree shift.
Just a question of interest.......If the above 2 sources in ATS; one from utility 120/208V 3 phase 4 wire and second 120/208V 3 phase 4 wire from secondary of our Dyn1 transformer; were to be 30 degree apart, then reconnecting DYn1 would not be possible to give 30 degree shift such that both sources become in sync. Correct ?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close