×
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

Calculation result from ETAP, LL & LLG fault is higer 3phase fault

Calculation result from ETAP, LL & LLG fault is higer 3phase fault

Calculation result from ETAP, LL & LLG fault is higer 3phase fault

(OP)
I've run ETAP program for isolated power system. The system consists of 3x6.5MW turbogenerator (10A NGR) supply 6.6kV motors and 2x 6.6/.4kV 3MVA DYN11 transformer (solid earth).
The calculation result surprise me and I would ask why this happen?
In which case that LL and LLG can go over 3 phase fault?
(I may go wrong with parameters of component.)

Thanks for help.

RE: Calculation result from ETAP, LL & LLG fault is higer 3phase fault

This is typical behaviour close to the generators because the zero sequence impedance of the synchronous machines is low.

RE: Calculation result from ETAP, LL & LLG fault is higer 3phase fault

Scotty, wouldn't the 10A NGRs negate the low Z0 of the turbo-gens contributing to a SLG fault?

RE: Calculation result from ETAP, LL & LLG fault is higer 3phase fault

When looking at a line to line fault the addition of 10 Amps to ground has negligible effect.

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

RE: Calculation result from ETAP, LL & LLG fault is higer 3phase fault

My mistake, I thought the original poster was also asking about SLG faults.

RE: Calculation result from ETAP, LL & LLG fault is higer 3phase fault

I wouldn't have thought a L-L fault could exceed a L-L-L fault. Neither have any zero sequence influence. As scotty said, the low zero sequence close to a generator can definitely result in L-L-G and L-G faults higher than L-L-L.

RE: Calculation result from ETAP, LL & LLG fault is higer 3phase fault

Correction to my post above. L-L can exceed L-L-L, but that is related to negative sequence impedance being lower than positive sequence impedance, which of course can occur with a generator.

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