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 Post subject: Pressure Rise in Enclosure due to ArcingPosted: Tue Nov 18, 2014 6:57 pm

Joined: Tue Oct 16, 2012 5:18 pm
Posts: 3
Hi,

Can somebody point me in the direction of how to calculate pressure rise within an IP (not flameproof) enclosure?
I am looking to assess enclosure strength vs. pressure rise at this stage - without the need for venting.

Thanks,

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 Post subject: Re: Pressure Rise in Enclosure due to ArcingPosted: Sat Nov 29, 2014 7:36 pm
 Plasma Level

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
CIGRE has a model for vented enclosures with a lot of data. Pressure rise has a lot of variables but the big thing is that it is linear and fast. Enclosure probably won't make it even 2 cycles.

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 Post subject: Re: Pressure Rise in Enclosure due to ArcingPosted: Sun Nov 30, 2014 8:30 am
 Plasma Level

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
Pressure rise=(kappa-1)*Kp*Parc*t/V
Where:
Kp is a parameter describing what amount of energy in the arc is transferred to heating air. It runs from 0.4-0.65. I think the arc power modelling is off so this would account for some of this. Also this is electrode dependent though arcs are electrode dependent.
Parc is arc power (arc voltage x arc current). The model uses the Lee assumption so Iarc is 1/2 of short circuit power. Its not clear as I mentioned if this messes up the Kp factor but it looks like it.
t is time
V is volume

I would encourage reading the entire CIGRE report because it gives a lot of background and assumptions although the focus is on designing a tool for arc resistant gear. After getting units right and putting in reasonable values I quickly came to the realization the keeping the doors on requires arresting arcing in only 1-2 cycles. This is barely within the capabilities of some molded case breakers and nothing in medium voltage short of some exotic stuff. That means recognizing an arc and tripping in 1/2 cycle, and opening in about 1 cycle.

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