×
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

SC Current on Primary

SC Current on Primary

SC Current on Primary

(OP)
If I am given a maximum fault current at a transformers secondary from the utility and the transformers impedance, how do I get the fault current that is seen at the primary side of the transformer (in order to get clearing times with the transformers protective device).

Xmfr: 3 phase, 150Kva, 12.47->120/208, Fault Current: 32,784 Amps, Impedance = 1.9%

Thanks.

RE: SC Current on Primary

If I'm punching the buttons on my calculator correctly you don't have 32,784 Amps of fault current on the secondary of the transformer, the most you have is 21,930 Amps based on an infinite bus connected to the high side of the transformer.

But for what ever fault current, the primary 3-phase fault current would be 208/12470 times the secondary fault current.

RE: SC Current on Primary

You didn't state if this is for a 3ph fault, or for some other condition.  The phase-group of the xmfr may be important.  

For example, a delta-wye-gnd transformer will have two primary phases contributing to a secondary fault, each at 1/sqrt(3) magnitude w.r.t the line-to-line turns ratio * sec current.

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