×
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

Delta start transformers orientation

Delta start transformers orientation

Delta start transformers orientation

(OP)
I think I have read it somewhere that delta usually faces the power flow direction, I wonder why it is like that?

If the start faces the power flow direction, we may get a float voltages on the secondary (delta), however, if the transformer is not earthed (star), this may lead to similar problem.

If we have a static converter, would it make a difference to face the power flow with a star instead of delta? i.e. delta will be connected to bridge rectifier.

RE: Delta start transformers orientation

A wye/delta may be problematic. If the wye point is left floating the transformer may develop transient overvoltage upon energization. If the wye point s connected to the system neutral directly or through a ground connection, the delta may transfer power between phases.
Any voltage unbalance or phase angle errors will result in circulating currents in the delta limited by the transformer impedance and the source impedance.
Issues:
1> In the event of a ground fault on one primary phase the other two phases will back feed into the fault and the fault current may be higher than expected.
2> In the event of a ground fault on one primary phase the wye/delta bank may blow a primary fuse.
3> In the event that one primary phase is lost, the wye/delta bank will back feed the missing phase. As a result, the wye/delta bank often blows a primary fuse due to overloading.
4> Repair crews have a tendancy to increase the size of primary fuses at banks experiencing frequent fuse blowing. Burned out transformers due to a combination of a loss of one primary phase and over sized fuses are another issue.
5> Distribution transformers are designed for low impedance and are as a result a small voltage or phase angle error will cause quite high circulating currents.
6> Long distribution lines with unbalanced single phase loading are apt to have voltage balance issues.
7> When long distribution lines with unbalanced single phase loading have voltage balance issues, the issues are often addressed by the installation of a bank of single phase voltage regulators. Unfortunately, when unequal line to neutral voltages are corrected by three single phase voltage regulators, line to line voltage unbalances are introduced and phase angle errors are introduced. The voltage and phase angle issues cause heavy circulating currents in a wye/delta bank.
8> When a distribution circuit with a wye/delta bank installed somewhere is energized phase by phase, Refrigerators and freezers on single phase transformers throughout the circuit are severely stressed and may fail.
9> It is well to use caution when considering a delta/wye bank in a co-generation application or any circuit where the power flow may reverse. Should the power flow through a delta wye transformer reverse for any reason the transformer is now a wye/delta transformer and may experience issues.
Other than that and a few things I may have forgotten, a wye/delta bank works great.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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