At my construction site hrere, we have an existing 25kV substation with a new 35kV substation being added right beside it. We wanted to tie our new ground grid into the existing groung grid (on a shutdown, of course) so we could backfill everything and get it out of the way. The 35kV sub is far from complete, and the engineering firm said this would force us to treat the new sub as live. We find this stupid because the grids are sharing the same earth side by side! Does anyone agree or have some input?
Substation ground grids.
- Thread starter pilsner31
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zog
Senior Member
- Location
- Charlotte, NC
As I understand this, you want to shutdown the old sub, tie in the grid for the new sub to the old sub and then renergize the old sub, is this correct?
If so, I would agree with the engineering firm, after the new grid is tied to the old grid the new grid and anything attached to it should be treated as energized.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
For those of us on the sidelines, just what does it mean when you treat a grounding grid as energized? What sort of PPE or procedure changes are required to work on the grounding grid or structures bonded to that grounding grid?
-Jon
-Jon
Foundation grounds
Foundation grounds
I am being told that a Traction Power Substation (for a Light Rail System) needs to have a ground wire from the slab foundation rebar or pier rebar tied to the ground mat of the substation (13.5KVA). This is in addition to the interior building halo ground system to the ground mat. Is this true? And where in the NEC or NFPA codes does this requirement show up?
Thanks
Foundation grounds
I am being told that a Traction Power Substation (for a Light Rail System) needs to have a ground wire from the slab foundation rebar or pier rebar tied to the ground mat of the substation (13.5KVA). This is in addition to the interior building halo ground system to the ground mat. Is this true? And where in the NEC or NFPA codes does this requirement show up?
Thanks
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Very simplistically.
The existing yard ground grid is bonded to all of the yard equipment, so that during a fault (even a lightning strike miles away) a person's feet and anything they touch is all at the same elevated (not zero/ground)potential. By connecting the new grid to the old grid, during a fault in the old yard everything connected to the grid in the new yard may become experience a rise in potential (i.e. become energized).
brian john
Senior Member
- Location
- Kilmarnock, Va
- Occupation
- Retired after 52 years in the trade.
Jim:
With existing substations this potential risk always exist, what precautions should the poster take, should they decide to join the two grids. Secondly depending on the soil type just being in the proximity of a substation doesn't this potential risk exist? based on the source voltage, magnitude of the fault and duration of the fault?
With existing substations this potential risk always exist, what precautions should the poster take, should they decide to join the two grids. Secondly depending on the soil type just being in the proximity of a substation doesn't this potential risk exist? based on the source voltage, magnitude of the fault and duration of the fault?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I meant to give a very simple answer. The real problem occurs when the new grid is not bonded to all of the equipment. Each new component would need to be bonded immediately as it is set in place to prevent touch potential. And yes during a nearby fault the soil conditions will dictate the potential of the surrounding areas but this would be true even if construction was not occurring, this is why some people never touch things anywhere near a switchyard.
zog
Senior Member
- Location
- Charlotte, NC
I feel safer in a switchyard than near one.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
brian john
Senior Member
- Location
- Kilmarnock, Va
- Occupation
- Retired after 52 years in the trade.
So if the OP were to install the new grid he would be better off with it connected to the existing grid, if they immediately bonded and new equipment as soon as it hit the site.
Would they be better off to bond it prior to setting it on the ground as it hung in the air on non-conductive straps.
Would they be better off to bond it prior to setting it on the ground as it hung in the air on non-conductive straps.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
That would depend on the voltage level of the yard, weird things, like induced voltages, can happen above 100kV.
Inspectorcliff
Senior Member
- Location
- Colorado
OMVHO, in my years of dealing with 69k transmission lines feeding 7200 subs and on occation 4160 subs, we always installed the ground grid, the isolated ground, the fencing, the bonding of the panels, the substation gear and did a resistance test to the isolated ground, prior to energizing the gear, IF, there was a fault current to occur, we had built a road for it to travel (we always hoped anyway). Good Luck.
Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
even if it's a ground, even if it's buried in the same dirt, connected is
connected.... i'd find and mark the existing ground grid, and run my grid
right up to it, but not connect to it. for 34.5 kv, i'd keep them 8' away
from each other, and mark the ends well... (turn them up, and sleeve
them in 2" pvc, to make them easier to find later.
when your sub is done, you are gonna have a major clearance pulled
to connect the sub up, and i'd cadweld them at that time....
randy
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