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11-04-2009, 08:48 PM
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#1
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Burger Flipper
Join Date: Aug 2007
Location: Bay Area, CA
Posts: 1,763
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Substation video - I got a question.
This is a 10 second video of what looks like wires being blown up, and it looks like it was planed. Can anyone tell me what is going on here?
http://www.youtube.com/watch?v=DCyMS...eature=related
~Matt
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11-04-2009, 09:25 PM
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#2
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IBEW Local 970 Member
Join Date: Mar 2008
Location: Longview, WA
Posts: 260
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I'd say someone did't remove the safety grounds, before they closed the breaker.
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11-04-2009, 09:27 PM
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#3
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Burger Flipper
Join Date: Aug 2007
Location: Bay Area, CA
Posts: 1,763
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AHH Whoops!!
~Matt
__________________
I would rather beg for forgiveness then beg for permission.
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11-04-2009, 11:07 PM
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#4
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Senior Member
Join Date: Apr 2009
Location: Charlotte, NC
Posts: 760
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Those are protective grounds but that was a test, conducted by AB Chance if I recall.
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11-05-2009, 12:14 PM
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#5
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Bilge Rat
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 652
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Energizing an indoor metal-clad medium-voltage switchgear with the ground set still connected is MUCH more ugly!
Rob
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11-05-2009, 04:10 PM
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#6
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Licensed Journeyman
Join Date: Oct 2007
Location: third world
Posts: 1,628
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Did the product pass or fail the test?
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“Dammit, Smithers, this isn’t rocket science, it’s brain surgery!”
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11-05-2009, 04:15 PM
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#7
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Senior Member
Join Date: Nov 2009
Location: USA
Posts: 243
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Quote:
Originally Posted by nolabama
Did the product pass or fail the test?
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I was wondering that too. Is there supposed to be a dangerous blast like that?
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I'm going back to work on Friday, no more time for foruming. Bye everyone!
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11-05-2009, 04:32 PM
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#8
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Licensed Journeyman
Join Date: Oct 2007
Location: third world
Posts: 1,628
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If it is a ground strap that is designed to protect personnel I believe it should be able to handle the energy without energizing the line. I don't know that, however.
__________________
“Dammit, Smithers, this isn’t rocket science, it’s brain surgery!”
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11-05-2009, 08:19 PM
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#9
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Bilge Rat
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 652
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A ground set might kinda, sorta, almost protect a person from the line being energized, but it's main purpose is to ground out induced voltages. If the protection relays were set fast and low, you'd likely be OK.
I never trust a ground set to protect me from a line being energized. I always disable the line some other way. A lot of guys don't though....
In an overhead line that's not grounded, voltage can be induced by capacitive coupling from other lines, static from wind, and a lot of other sources. If the line has been isolated for a while, and the ground set is attached, I've seen arcs an inch or two long. A nice little SNAP!!
Hint; make sure you attach the ground side first!
Rob
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11-06-2009, 08:59 AM
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#10
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Senior Member
Join Date: Apr 2009
Location: Charlotte, NC
Posts: 760
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Protective grounds need to be rated for the available fault current in the system they are being installed on, they serve 3 functions.
1. To dissapate any induced or stored energy on the line
2. To create a 3 phase fault and trip the upstream protective device in case the line accidently becomes energized
3. To create a zone of equilized potential during the period of time the line is energized.
Proper installation is vital for creating an equipotential zone. For example, indoor 15kV switchgear, the ground is attached to the ground bar in the switchgear which is bonded to the substation ground, including the rebar in the concrete floor you are standing on. If the system becomes energized the line, the metal enclosure, and the rebar under your feet are all energized to the same potential (Until the OCPD activates) eliminating any voltage drop across the workers body.
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