×
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

high voltage transformers

high voltage transformers

high voltage transformers

(OP)
Can someone please help. I would like to know, why most HV transformers are connected Star-Delta, either on the primary or on the secondary. Does it have to do with the fault levels, or not. Why not just connect it Star-Star.

RE: high voltage transformers

A delta primary/star secondary distributes unbalanced loads on to the supply better.
A three legged, three phase transformer core will often over heat unless it has a delta winding to accomodate third harmonic magnetic flux, and unbalanced flux due to unbalanced loading.
Some transformers have a delta tertiary winding for this reason.
respectfully

RE: high voltage transformers

Another advantage of delta-wye configuration is that ground faults on one side are not seen as ground faults on the other side - no zero sequence current can flow through the transformer.  This greatly simplifies relay coordination and improves selectivity on ground faults.

RE: high voltage transformers

See if you can find a copy of an old GE paper - The Why's of the y's.  The paper shows why y-y transformers are not generally used - although if they are shell type the 3rd harmonic problem is not present, but with core-type or three separate transformers, you end up with large 3rd harmonic voltages and bad regulation.

RE: high voltage transformers

Most HV transformers are Wye-Wye since essentially all HV transformers are used in the bulk power transmission system.  Distribution, at Medium Voltage, may use Delta-Wye or it may use Wye-Wye; lots and lots of three-phase Wye-Wye transformers in use between the MV distribution system and the LV services.  Quite often the HV-MV transformers that separate the transmission system from the distribution system are very often Delta on the high-side and Wye on the low-side.

RE: high voltage transformers

(OP)
thanks for the feed back guys.

RE: high voltage transformers


Some info on different transformer connections:

http://www.beckwithelectric.com/powerlines/powerlines-37.html

In addition to the previous posters:
Winding configuration: A lot depends on application and maybe in a lesser extent on previous history. Like David said, star-star transformers are still used. Another application for star-star trsfs are as station transformers in  Power station auxiliary systems.

Star connections are usually preferred on the LV-side for grounding issues. To prevent zero-sequence currents flowing through the trsf, the HV-side is normally connected in delta (like stated by dpc)

On higher voltages windings (windings subjected to a voltage of 66kV and higher) are connected in star, because, in a star-connection, the winding isolation can be degraded towards the neutral point. (More Insulation = more money) In the case the secondary might be delta (preventing through-flow of zero sequence currents) or star, depending on the application.

Regards
Ralph


Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon

Make the best use of Eng-Tips.com
Read the Site Policies at FAQ731-376

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