×
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

Fault Current Calculation

Fault Current Calculation

Fault Current Calculation

(OP)
Ok, So I have
X/R Ratio
Peak fault Current
RMS fault Current
of a 33kV nominal network
How do I calculate the specific X and R values from this for a netwrok infeed, ETR 120's just confusing me...
And how do I calculate the equivalent network infeed
I think it would be
S = (V*V) / (SQRT((X*X)+(R*R)))

RE: Fault Current Calculation

Hi,
From what I have understood,
you have a RMS fault current, take its reciprocal multiply by the base MVA and you got it.
cheers !

RE: Fault Current Calculation

Is this a homework? Sounds like one...If so should not be supported here.

RE: Fault Current Calculation

(OP)
No its not homework, I'm trying verify the results I get from a new piece of software but my basic knowledge has gone out of the window...

RE: Fault Current Calculation

I dont think you can calculate X/R ratio with the information you have. You will have to know phase angle of the SCC, if you want to know. Or you will have to know X and R values of all the componets from sources up to the fault location. In many case the utiltiy co has provided me with Thevenin's equivalent of their network which will give you X and R values.

In most cases, the sofware asks for or assumes a default value of the X/R ratio which for a 33kV system could be 8, 10, 12 or 15 at the max. Also it depends on the purpose of you analysis also. If this is for sizing ratings of 33kV or lower equipment, above assumption would suffice.


RE: Fault Current Calculation

By the way refer to IEEE Buff and/or the Red book for refreshing the basics.

RE: Fault Current Calculation

(OP)
>>>rbulsara>>>
Cheers for that, and I'll check out red book too

Would this be acurate enough for getting X and R from the ratio?

X = Z sin ([tan-1](X/R))
R = Z cos ([tan-1](X/R))

And then sizing a slack bus according to the RMS fault contribuiton

RE: Fault Current Calculation

The formulas are correct, resultant X and R will be as accurate as the assumption of the ratio. How will you get the Z however?


RE: Fault Current Calculation

(OP)
ah.. you've got me there....
I've seen this used before
S being the rating of the Slack Bus

S=(V*V)/Z

Now if the slack is given the stated RMS fault contribution from the network we have S and V so Z is easy to get... however, how accurate do you think this would be?

RE: Fault Current Calculation

Now I am more confused as to what you are trying to do.

Plus I do not know what a Slack bus is. May be you can explain little more or someone else can chime in..

RE: Fault Current Calculation

To calculate the X/R ratio from the peak and Rms current check the IEEE 242 -2001 chapter 2.4 (eq. 2-3)

RE: Fault Current Calculation

Re-reading your post..you already have x/r ratio.

Then what Cooda76 said is correct method to find Z.

Then use the formulas you indicated for R and X in your second last post. I think you have it there..

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