Ground Grid Study: Short Circuit Current Analysis

[tr0ypayne]

Short Circuit Current

Hi,

I am reviewing a ground grid study of a substation for a wind farm that is being built. The ground grid will be for a substation with a low side of 34.5kV and two transformers that step the high side voltage up to 345kV. There are six distribution feeders on the low side coming from the wind farm generation and the step up transformers are wye/wye. My question is why was the short circuit current (6.399kA) of the high side used on the ground grid study and not the low side current (26.825kA)? Is this correct? I would think the load side short circuit current would be used since it is larger.

Can any of you give me some insight into this?

Thanks,

Troy

 

[dlgoff]

Hi tr0ypayne and welcome to PF.

I'm really no expert here but I did work for an electrical utility for a number of years. When we did ground resistance studies we would take resistance readings from the ground grid to points at varying distances out and along the transmission line. The idea was that if the high voltage line should make contact with the earth, ground rise potential would be minimized. (the low side potential is low enough as to not be the major problem) I worked with the SCADA side of the utility and these studies were required by the telco so that high currents didn't get into their system.

You might want to PM M.S.J as he seems to know a lot about power transmission.
Here's his profile page: https://www.physicsforums.com/member.php?u=84682"

Hope this helps a little.

Edit: Here's an ipaper that might be of interest.
http://www.scribd.com/doc/11358767/IEEE-Std-10501996" [Broken]

 

[tr0ypayne]

Thanks for your help and thoughts. I will send M.S.J. a message. And I am also looking forward to talking to you again when I have a SCADA question.

Thanks again.