It is currently Sat Nov 18, 2017 10:09 pm



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Breaker Racking Arc Flash Video
PostPosted: Thu Aug 07, 2008 11:37 am 
Offline

Joined: Mon Jul 23, 2007 6:49 am
Posts: 19
Zog wrote:
Take this racking accident for example, no exposed live parts here
http://www.liveleak.com/view?i=995_1213752982


Does anyone know the details of this event?

It looks like it lasted several seconds based on the video time which leads me to believe the main did not trip right away. Doors open, tight space etc.

I guess people that moan about category 4 PPE should see this.

What are everyone else's thoughts?


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu Aug 07, 2008 11:55 am 
Offline
Plasma Level

Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
K. Jackson wrote:
Does anyone know the details of this event?

It looks like it lasted several seconds based on the video time which leads me to believe the main did not trip right away. Doors open, tight space etc.

I guess people that moan about category 4 PPE should see this.

What are everyone else's thoughts?


I think that was the main, so you are waiting for the fuses to clear on the primary side of the transformer which is typical.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu Aug 07, 2008 6:36 pm 
Offline
Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 480
Location: New England
How could it have been the main? The lights were on till the fault so the main was closed. It looked as if the tech was racking out or in the breaker. If he were racking out the main he would have lost his lights. Guess it could have been a double ended sub. The other possibility is that he was on a branch breaker, and the Main took a while to clear. Mains normally don't have Instantenous functions and their short time delay is usually at the highest setting, plus you can often add delay time to the main with dip switches. The other thing I find often is that all the breakers are set too high. People don't realize how much impedence the utility adds for finite bus calculations. Historically, if we did do a correct fault study, we would set the breakers to react to expected 'bolted' fault current levels. Arcing Current is often 50% to 70% of bolted fault. So an arcing fault may be low enough to keep the breaker in its long time delay portion of the curve.


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu Aug 07, 2008 8:01 pm 
Offline
Plasma Level

Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
haze10 wrote:
How could it have been the main? The lights were on till the fault so the main was closed. It looked as if the tech was racking out or in the breaker. If he were racking out the main he would have lost his lights. Guess it could have been a double ended sub. The other possibility is that he was on a branch breaker, and the Main took a while to clear. Mains normally don't have Instantenous functions and their short time delay is usually at the highest setting, plus you can often add delay time to the main with dip switches. The other thing I find often is that all the breakers are set too high. People don't realize how much impedence the utility adds for finite bus calculations. Historically, if we did do a correct fault study, we would set the breakers to react to expected 'bolted' fault current levels. Arcing Current is often 50% to 70% of bolted fault. So an arcing fault may be low enough to keep the breaker in its long time delay portion of the curve.



Most plants feed the substation lights from a different part of the system so that dosent happen. The setting s that you find are always high are probally from the electricians turning them up after a breaker trips, some think thats what was wrong "The dang breaker was set too low" :-)


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Aug 11, 2008 11:36 am 
Offline
Plasma Level
User avatar

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1216
Location: Scottsdale, Arizona
This certainly did not have a good ending.

Does anyone know the actual outcome or what caused the event?

It looks like the switchgear is medium voltage since there seem to be relays in the doors. It also looks like the person was wearing a face shield and maybe category 2 clothing but it is a little hard to tell. I agree it does look like it took a few seconds to clear so there must have been some really high time dial settings.

It is pretty ugly but it does show the need for flash suits when conducting work like this (although I bet this was greater than 40 calories)
It also shows how important quick clearing times are even though that could be in conflict with coordination.

_________________
Jim Phillips, P.E.
Brainfiller.com


Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue Aug 12, 2008 7:50 am 
Offline

Joined: Mon Aug 11, 2008 5:00 pm
Posts: 24
I wonder if there even was a main? Perhaps these were all feeders? It does appear to be an unusually long clearing time.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
cron
© 2017 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883