Reduction in ground fault current

[sobeys81]

Hi,

I was wondering, if during a ground fault on the primary of a 44 kV transformer in a substation, if the system feeding the fault is a 3 Ph 4 wire system and the fourth wire could be either Neutral or ground and this wire is connected to the grounding grid being designed.

Major part of the ground fault current will flow back through this fourth wire. I was just wondering, when I have to consider fault current for GPR calculation, Will IEEE, inspection authoritry or common sense allow the design of grid based on the current flowing through the ground grid(earth) rather designing based on total ground fault.

Will it matter if the forth wire from the utility is a Neutral or ground.

 

[jghrist]

Yes, you should consider that only part of the return current will flow through the ground grid and earth. Part will flow through the neutral/ground/shield wire. It doesn't matter what the fourth wire is called as long as it is connected to ground at both ends (and probably at each structure). See IEEE Std 80 for methods of determining the current split.

 

[sobeys81]

Thanks Jghrist. I always forget my username and I have to create new ones. You will not recall but two yrs ago you had a significant contribution in making me understand the whole grounding issue. I always will be grateful. I am sure your hourly rate will be more than I can afford for you valuable advise.

Anyways, I will revise my grounding concepts and read IEEE-80.