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

Sizing Buried Delta Winding Current Transformer

Sizing Buried Delta Winding Current Transformer

Sizing Buried Delta Winding Current Transformer

How does one calculate how much zero sequence will flow in a YYg transformer with a buried tertiary delta winding during normal operation to size the ratio of the CT on the winding?


RE: Sizing Buried Delta Winding Current Transformer

During normal operations it should be near zero. System imbalances will result in some, but just a few percent of total current.

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

RE: Sizing Buried Delta Winding Current Transformer

Thanks David, that is interesting because I have seen engineers size this as really high CT ratios compared to the phase CTs. We don't have any real intention to use it for protection so was just going to monitor zero sequence currents with it. Perhaps we should just remove this CT then or is there any value in keeping it?

RE: Sizing Buried Delta Winding Current Transformer

In a wye/delta transformer, the zero sequence impedance is three times the positive sequence impedance.
A small imbalance on a transformer with relatively high impedance will generate a relatively low circulating current.
A large imbalance on a transformer with a relatively low impedance will generate a relatively high circulating current.
Transmission lines typically have well balanced loads and voltages and relatively high impedance transformers.
A delta tertiary winding may provide beneficial stability and balance to a transmission circuit.
Distribution circuits typically see lower impedance transformers and often unbalanced loads.
Grounded wye/delta configurations are best avoided on distribution circuits.

Ohm's law
Not just a good idea;
It's the LAW!

RE: Sizing Buried Delta Winding Current Transformer

Heavy current will flow inside the stabilizing tertiary winding during an LG fault on secondray side. To give an idea of current, in a typical 10 MVA 132/11 unit, Vz= 10 %, the tertiary winding will see 3 times rated current without LV feed and may increase above 7 times with LV feed.
In small transformers we eliminated stabilizing winding in India due to tertiary winding failures from the dynamic forces consequent to over currents during LG faults on secondary lines.

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


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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