×
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-Wye Transformer load distribution panel connections

Delta-Wye Transformer load distribution panel connections

Delta-Wye Transformer load distribution panel connections

(OP)
We have a 12.5KV Delta to 480V Wye 3 phase transformer in the MCC.  The secondary is wired 4 wire to a Wye type 480V 3 phase distribution panel.  We have connected three loads through breakers to the panel: a 480V 3 phase Delta to 120V Wye stepdown transformer for 120V loads; and two (2) small VFD's, both with 480V 3 phase Delta inputs.
When we closed the breaker for the transformer, it blew in less than 2 days.  When we closed the breaker on each of the VFD's they blew in less than 10 seconds, each time taking out the 225A main on the distribution panel.  We are now $30K into this disaster.  Can anyone tell me what we have overlooked and done wrong?

RE: Delta-Wye Transformer load distribution panel connections

Need more information.  We get the picture but now need some specifics.

What model VFDs?
What HP motors?
How far are the motors from the VFDs?

Are you saying either VFD breaker closing will blow the main, or only both?

Got ratings on the transformers?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Delta-Wye Transformer load distribution panel connections

In addition to the information itsmoked requested:

Quote:

When we closed the breaker for the transformer, it blew in less than 2 days.
I assume that you mean the 12.5kV primary transformer.

Have you measured your voltage phase to phase, phase to neutral, and phase to ground on the 480V?

What other kinds of loads do you have in the 12.5kV MCC?  Are you certain it is a 12.5kV MCC?

What is your protection scheme on the 12.5kV transformer. What are the three breaker sizes on the 480V distribution panel?

RE: Delta-Wye Transformer load distribution panel connections

What are the device settings?  What does the coordination study say the settings should be?  What does the load flow study say the loading will be?  Is there a problem or is equipment just misapplied?

RE: Delta-Wye Transformer load distribution panel connections

Is your MCC running at 12.5kV or is the 12.5:480/277 transformer feeding the MCC.
Have you grounded the wye point of your 480/277 volt system?
An ungrounded system fed from a 12.5 kV transformer is a good candidate for suspicion.
respectfully

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