Confuse with earth Ground simulation - CYMGRD

[slugz]

Hi Guys,

I'm doing some simulations on software CYMGRD for earth substation, and i am really need some light on that..

Informations to do mesh:

BUS 138kV - ICC = 7kA - Remote contribuition 100%
BUS 13.8kV - ICC = 12kA - Remote contribuition 0% (dont have neutrals).

In my country they don't use neutrals on feeders..So i made simulations based on this.
I attach a picture to understand parameters.

My doubts:
1) When i change remote contribuition in BUS 13,8kV to 60% the software make calculations based on 12kA. But below 60% (0% at 59%) software does simulations based on 7kA (BUS 138kV), why?
2) Why software consider ICC 7kA and not 12kA? I understand that a 12kA LG fault is worse that 7kA.

i know there is a SF and DF (split factor and decrement factor) but i cant understand why 7kA are consider for calculations and not 12kA...

Can anyone shed some light on it

Thanks for your time...

DOWNLOAD PICTURE FILE -->

http://files.engineering.com/getfil...f2-496e-8430-3deebe12a89a&file=Earth_Grid.jpg

 

[Desrod2]

Look like a missing/incorrect configuration. This is a perfect case for software support. Why not contact CYME directly? They should be able to solve that with a phone call with one of their engineers.

 

[cuky2000]

Slugs, the suggestion from Desrod2 could help to expedite the modeling of your system.

Here is a couple remarks to keep always present for grounding analysis:
1) The relevant current is the one injected into the earth and travel to the source in this path.
2) If there is no neutral, continue ground conductor or shield wire, 100% of the ground fault in the substation travel to the source via the earth path.
3) Systems with delta or wye ungrounded transformer block the zero sequence and therefore not ground fault current travel from/to the remote source.

 

[jghrist]

The 12kA 13.8 kV fault is all local source and doesn't flow through the earth to return to the source (all return through ground wires. Only the 7kA 138 kV fault hE to flow through the earth.