×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!
  • Students Click Here

*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

Jobs

Three-phase transformers connections

Three-phase transformers connections

Three-phase transformers connections

(OP)
I’m not quite clear about three-phase connections that are in use. For example: in Europe is in use 63 MVA, 110/35/10 kV, YNyn0d5 three-phase transformer with both neutral points grounded. I assume that magnetic core has three legs (I didn’t actually saw it so I’m not sure). The 35 kV network is not grounded on the other end which means that there is no zero-sequence component of current (except in short-circuit fault with earth but thats is very short period of time. My question is: "Why do we need tertiary winding when there is no zero-sequence component of current and the form of magnetic flux is good (flux' third harmonic is small because of the magnetic core shape)?"
Second question is: "Are there three-phase power transformers with five legs magnetic core? If there is, please specify me they rated power, voltages and connection"
Please somebody answer! Thanks for your time.

RE: Three-phase transformers connections

Cubrilo—It appears you may prefer an answer in IEC-based standards, but IEEE C57.105-1978 IEEE Guide for Application of Transformer Connections in Three-Phase Distribution Systems addresses the matter also.  See: §3. Magnetic Circuits, §5. Primary Faults and §6. Unbalanced Loads and Secondary Ground Faults  It is usual for these standards to have a very detailed reference list for further studies.  INDEX at: http://standards.ieee.org/reading/ieee/std_public/description/dtransformers/C57.105-1978_desc.html  ;
Guide for the Application of Neutral Grounding in Electrical Utility Systems, Part V Transmission Systems and Subtransmission Systems  INDEX at:
http://standards.ieee.org/reading/ieee/std_public/description/surge/C62.92.5-1992_desc.html  ;§6. Transformer Tertiary Systems

With ∆ tertiary, it is customary to keep these external connections quite localized, as ground faults on the associated bus are somewhat more difficult to detect, but the winding is essential for maintaining zero-sequence currents in the Y windings.  A single CT placed in the tertiary “loop” can provide polarizing quantities for primary- and secondary-side relaying.  
  
Thread238-24305

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!


Resources