Arc Blast Pressure
Arc Blast Pressure
(OP)
I am trying to calculate pressures developed by electrical fault. I 've come across formula published in h ttp://ecmw eb.com/mag /electric_ putting_ar cflash_cal culations/ from Ralph Lee's paper, "Pressures Developed by Arcs":
Pounds/ft^2=(11.5×kA arc)÷(distance from arc in feet)^0.9
There are also other publications referring to the same source. My concern is that arc pressure in the formula above does not depend on system voltage. Arcing energy is a function of voltage and arcing current. Does anybody know why the pressure does not depend on voltage? Please correct me if I am missing something.
Pounds/ft^2=(11.5×kA arc)÷(distance from arc in feet)^0.9
There are also other publications referring to the same source. My concern is that arc pressure in the formula above does not depend on system voltage. Arcing energy is a function of voltage and arcing current. Does anybody know why the pressure does not depend on voltage? Please correct me if I am missing something.






RE: Arc Blast Pressure
You are saying you think the arc is more related to power than then to current? I would argue, "why are arc welders all about current?"
Keith Cress
kcress - http://www.flaminsystems.com
RE: Arc Blast Pressure
RE: Arc Blast Pressure
RE: Arc Blast Pressure
During an event a lot of the voltage drop would be in the supply network I doubt you would see the 5kV across an actual arc. But that is really a guess on my part.
Again its the current that is providing the media of the arc. Not the voltage. If you have high voltage and less current you just have a spark.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Arc Blast Pressure
RE: Arc Blast Pressure
RE: Arc Blast Pressure
RE: Arc Blast Pressure
RE: Arc Blast Pressure
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Arc Blast Pressure
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Arc Blast Pressure
Bill
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"Why not the best?"
Jimmy Carter
RE: Arc Blast Pressure
RE: Arc Blast Pressure
Thinking back to some of the more theory related stuff in school, and about static electricity, a couple things come to mind: static electricity has an exceptionally high voltage (electric field) but very little capacity to cause high pressure in an 'arcing' condition.
If you looked at the electric field in a static electricity (putting shirt on, etc) situation, you would find the electric field would be high magnitude in a very thin line from one surface to another. So, there's only so many electrons that can flow in this relatively small cross section of the electric field that is capable of moving electrons in an arc. Additionally, there's only so many electrons concentrated on the surface of your material before they flow over to your other surface, and then your electric field drops down because there's quickly equipotential on both surfaces.
In an arc flash scenario, however, once you breakdown the air or whatever is between your two surfaces of different electric potential, there's going to be substantially more cross sectional area of electrical field lines that can carry current. And a greater supply of electrons for that matter. Your generator or whatever is supplying your system makes sure of that until your fault is cleaered.
Skogs, although I think I see what you are getting at, I think you should expand upon your 'negative resistance' idea. Are you saying that an arc causes a negative slope in the I-V characteristic? I think that's what you're saying.
RE: Arc Blast Pressure
You can see this in any device that uses an arc. An arc welder, for instance. If there weren't any current limiting, it would not be possible to weld at all. The current would increase untill a breaker trips or a fuse blows.
Once the arc has started, the voltage across it is relatively constant. Independent of arc current. Actually, the voltage rises if you reduce the current down to the arc stability limit where the arc snaps off.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...