pole grounding 1

[metalgear15]

Good Day! can anyone here give me the pole grounding specification standards of your distribution systems, e.g.( method,resistivity,wires & rode dimensions,rod depth). just want to gather data on what other utility companies are thier standard on pole grounding. thank you very much for the replies! god bless

 

[MikiBg]

Hi,
You can find an example from Serbian distribution utility attached. Ring type of earthing electrode is chosen because of advantages regarding touch voltage reduction on small space available. For more rigid safety requirements, two earthing rings can be applied (right section of drawing). Hope you will find it useful.
Regards,
Miki

 

[metalgear15]

Thank you very much for the info this is very helpful. can i ask also how much resitivity do you get using this type of earthing? & what is the Serbian standard resistivity. i would appreciate again your reply.

 

[MikiBg]

According to formula that I have, a resistivity of ring with smaller diameter will be roughly 0.298*rho, and 0.179*rho, for ring with bigger diameter, where rho(ohm*meter) is specific resistance of surrounding soil. For rho=100 ohm*meter, in example, that means app. 30 ohm for smaller and 18 ohm for bigger ring. For both rings together is hard to tell, because of mutual influence between them.
Another type of earthing proposed is star type electrodes, because of their advantages in areas with big number of lightning strikes. Combination of rings and star type electrodes is also recommended.
A criteria for earthing resistance is possibility for pole insulation breakdown and hence impact on line conductors during lightning strike and it depends on peak value of lightning current and insulation level (permissible voltage). In practice, that usually means max 10 ohm for poles near substation and max 15 ohm for other poles. Besides earthing electrodes described above, pole foundation contributes to that desired value as well.
Regards,
Miki

 

[metalgear15]

Thank you very much again for all your inputs on my thread.I really appreciate it. God bless