×
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

Maximum earth grid current
2

Maximum earth grid current

Maximum earth grid current

(OP)
Hi everyone,
We are doing the earthing calculation for 33/6.3kV SS.
There are 2 nos. 33/6.3kV , 30MVA transformer Dyn11.

For calculating the maximum grid current, should we consider
- Maximum switchgear fault current
0r
- Transformer 3 phase fault current at Y side

thanks for helpful replies.

RE: Maximum earth grid current

A conservative approach could be taking as the maximum short circuit rated equipment, often driven by the SC rated of the switchgear.
 
If less conservative approach is desired for design purpose this could be a fraction of the maximum available short circuit plus a margin for grow.

This fraction of current is typically called split factor as shown in the link below.

http://cuky2000.250free.com/Gnd_Example_Current_Div_Factor.jpg

RE: Maximum earth grid current

Usually, you need to look at the maximum ground fault current on the high side of the transformer, with appropriate split factor as indicated by Cuky.  The current on the low side is usually not a factor because the return current does not flow through the earth.  There may be cases where the worst case is a low side fault away from the station where return current flows through the earth.  If the outgoing 6.6 kV lines have neutrals, generally most of the return current will be through the neutral except for currents distant from the station, but in these cases, the fault current is reduced.

RE: Maximum earth grid current

(OP)
Thanks,
Your replies really helped me.

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