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 Post subject: Case Study for Flashover
PostPosted: Mon Mar 02, 2009 10:11 am 
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i hv tis case study for my electrical safety and hazards subject.
we are required to study the case.

as below:

Image



can any1 explain more about it ?
dont really understand the term circuit spout.
how can flashover happen in tat small cubicle ?
how does the flashover happen when the discharge rod touched the main busbar ?

thanks alot.
i need extra information -)


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PostPosted: Mon Mar 02, 2009 10:49 am 
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Maybe it is common terms in the country this occured (Australia mate?) but the terms used in this are not common in North Amercia. There are several things that dont make sence in this senario but it appers they were attempting to discharge a MV cable prior to thumping to locate the fault and put the discharge stick on an energized cable.

The line side of this breaker should be the cables behind the yellow shutters, it looks like the flash occured on the load side (Bottom, exposed bus connections), maybe they had it backfed from another source.

Any more info on this?


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PostPosted: Mon Mar 02, 2009 6:05 pm 
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I am assuming the description states they grounded the "line" (Main) side rather then the "load" (Circuit) side of the the particular circuit. I would also imagine the switchgear originally had shutters on both line and load primary bottles (Spouts). I have been fault locating on medium and high voltage systems for over 20 years have have never attempted to access a metalclad switchgear primary stab. Just seems wrong to me.


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PostPosted: Mon Mar 02, 2009 6:31 pm 
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dpmac wrote:
I am assuming the description states they grounded the "line" (Main) side rather then the "load" (Circuit) side of the the particular circuit. I would also imagine the switchgear originally had shutters on both line and load primary bottles (Spouts). I have been fault locating on medium and high voltage systems for over 20 years have have never attempted to access a metalclad switchgear primary stab. Just seems wrong to me.


Very wrong. I had the same initial thought but if you look at the black marks on the door it lines up with the load side stabs, maybe the line side shutters were lified part way and deflected the arc down to make it look that way, you can see some black marks on the shutters between X and Y phase, hard to tell from those pics but I think this arc was load side stabs, X to Y (Or X or Y to grounded shutters).

BTW Nelsonboy, welcome to the forum.


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PostPosted: Tue Mar 03, 2009 1:25 am 
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thanks.

i jz approached my lecturer.
according to him,
the victim plugged the discharge rod into the mainbus bar instead of circuit busbar.
it is lived. tats y flashover occurred.

so what flashover means here ?
is it arcing ?
accordding to wiki, flashover needs time to occur. (thick black smoke,heating gas)
but in this case, it was instant.

another extra info is that,
the victim did not perform any lock out - tag out action.
the shutter should have thighten (for live busbar) after lock/tag out
but in this case, the live busbar shutter can be open.


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PostPosted: Fri Mar 06, 2009 7:07 am 
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Zog wrote:
Very wrong. I had the same initial thought but if you look at the black marks on the door it lines up with the load side stabs, maybe the line side shutters were lified part way and deflected the arc down to make it look that way, you can see some black marks on the shutters between X and Y phase, hard to tell from those pics but I think this arc was load side stabs, X to Y (Or X or Y to grounded shutters).

BTW Nelsonboy, welcome to the forum.


Have a look at the underside of the yellow (line-side) shutter. It has a burn mark on the lower edge. Looks like maybe the shutter was lifted slightly to get the probe in.


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PostPosted: Fri Mar 06, 2009 8:35 am 
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Goldenspark wrote:
Have a look at the underside of the yellow (line-side) shutter. It has a burn mark on the lower edge. Looks like maybe the shutter was lifted slightly to get the probe in.


I saw that but I think that was damage from the arc on the load side, the burn marks on the door clearly line up with the load side stabs.


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