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 Post subject: AC and DC Arc Fault Generator
PostPosted: Sat Apr 03, 2010 8:42 am 
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Bonjour,
I have done videos of my experiments. And i decided to show them to you, i was thinking it may be interresting.
Videos can be found here :
[url="http://www.youtube.com/user/djho123"]http://www.youtube.com/user/djho123[/url]
Those are 115V AC arc faults and 28V DC arc faults.
Slts


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PostPosted: Sat Apr 03, 2010 6:04 pm 
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Whats the distance between the electrodes. Are you saying you got 28VDC to jump that gap just by bringing the electrodes to that distance? How was the arc initiated.


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PostPosted: Sat Apr 03, 2010 6:12 pm 
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Yes, please provide some details on this test si vous plait.


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PostPosted: Sun Apr 04, 2010 2:28 am 
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Bonjour,
The arc is iniated with a High Voltage High frequency pulse added to the supply. This supply can be AC or DC. Because the overall generator is curently pattented, i can not explain with more details. But if you show my previous post, you will see that the first question i ask is about the the gap distance. I will ask my boss to obtain the rigth to show you my Voltage/ Current figures for different gap.

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PostPosted: Sun Apr 04, 2010 4:02 pm 
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That's a bit of 'trick' to bring to an arc flash forum. Your high frequency high voltage arc ionized the air significantly reducing its resistance. Try to test without the initial ionization and see what you get. I seriously doubt you could get 28VDC to arc, and 110V would need some very special circumstances.


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PostPosted: Mon Apr 05, 2010 3:00 am 
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A trick ? You say...

There is no trick in this experience made at the Laboratory of Instrumentation and Electronics of Nancy - Nancy University.
If you want you can meet me at the IEEE ISIE Conference in Italy this summer where I presents a paper reviewed by experts. Or meet me at the IEEE HOLM Conference in South Carolina in October where I present two papers : this testbench and a new electrical model of arc fault for circuit modelisation.


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PostPosted: Mon Apr 05, 2010 4:37 pm 
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djho wrote:
A trick ? You say...
No time to waste with you


I don't think Haze was saying that you were trying to fool anyone. It is just hard to see this able to happen without the pulse you had described, but with your post edited such as it is, that text is missing now.


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PostPosted: Mon Apr 05, 2010 6:28 pm 
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Yes, I don't mean to say you are trying to trick anyone, only that under the conditions of arc fault preparedness, one would not expect to encounter a high frequency high voltage pulse, on circuits of this voltage. The act of creating the pulse at those voltage levels is misleading, because under normal conditions you could not get them to arc with out some artificial method to initiate them.

You have to remember you are on an 'arc flash forum' and the debate of what can and can't cause a dangerous arc are constantly being debated.


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PostPosted: Mon Apr 05, 2010 7:26 pm 
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djho wrote:
A trick ? You say...
No time to waste with you


And with that sort of approach, no time to waste with you as well! Why don't you go dangle your baubles in front of someone else?


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PostPosted: Tue Apr 06, 2010 2:22 am 
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Sorry,
I was thinking that you were saying that I'm a liar. I will try to answer:

"one would not expect to encounter a high frequency high voltage pulse, on circuits of this voltage"... this assumption is false !!
Of course this kind of fault can appear !!! And espacially when a self is disconnected from the circuit thus producing an overvoltage of many kV on a simple 28V DC line. If the cables are aged and their insulators present holes, it is very easy to initiate this type of arc. Because you are focus on powerfull systems, generally 'fixed on the floor', you don't know that many lost connections in aircraft for exemples due to vibrations lead to overvoltage and then to fire with this type of initiation.

In aircraft, voltage are 28V DC and 115V AC, and we can found more than 30 crashes due to arc fault. So, how this kind of fault can appear if we consider you're right ? In fact overvoltage initiation is one of the 4 tests recommended by boeing to test AFCB.

There is so many ways to iniate arc beetwen two aged cables : overvoltage, direct contact, water insertion, liquid contamination, temperature and so on...
What is really important to me is not the way to initiate, but the way to detect the arc. Because it is a very fast pulse, you will 'not see it' on any records of voltage or current fault and more current voltage signals are the same as other ways to initiate. This is enough to develop and test arc fault circuit breakers.

What is extremly important to caracterize arc fault and test detectors is that this generator can do REPRODUCTIBLE and CALIBRATED arc faults. Classical systems to initate such as open circuit sytems are not able to do so.

I understand that here the main debat is how to secure electrical installation and prevents arc fault for safety. So you use appropriate design rules to do it. My problem is different, and you haven't got understood it first. In aircraft, there is no people operating in the electrical system. If there is an arc fault in flight the system must detect it and break the line, whatever the way the arc is initiated (the way the arc is initaited is simply not detectable).

Some aircrafts are flying for more than 40 years, and there is a lot of aged wires. Because we can't change all the wires in aged aircraft (due to the cost), the only way is to change common breakers by breakers with AFCB.

"that under the conditions of arc fault preparedness", it's rigth. As an exemple, atmospheric pressure is for you a condition of arc fault preparedness. But for aircraft it is not. At high elevation nearly 15 km (30 to 50,000 feet) the strike voltage is lower than in your application. So before we can debate, I ask you : what is the conditions of arc fault preparedness ? You seriously doubt you could get 28VDC to arc, and 110V would need some very special circumstances... in your application it is true but not in mine. Does this forum only concern conventionnal electrical systems ?


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PostPosted: Tue Apr 06, 2010 5:19 am 
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djho wrote:
Does this forum only concern conventionnal electrical systems ?

You keep editing your posts long after they are displayed . . .

I think that less conventional systems are fine to discuss here, IMO, but as we tend to start by considering the energies caused by the arcs that may occur while personel are servicing the systems, it helps if you state the background info.

I for one - and probably most others here - are interested to learn about any way an arc can be propagated, conventional or not. It does help to know where this is likely to happen though.


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PostPosted: Tue Apr 06, 2010 5:28 am 
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If you are looking to protect wiring, it sounds like these breakers are more for what the US industry calls arc-fault (AFCI) rather than arc-flash.


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PostPosted: Tue Apr 06, 2010 9:30 am 
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There is no french translation for arc-fault. And I do not know really the difference beetween arc fault and arc flash. Is it a matter of power ?
For sure if they were an arc fault forum, i will post in it !!! But there is no...it is so hard to find people interresting in arc fault and even an arc flash. So it is a real chance for me to talk with you about arc problems.


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PostPosted: Tue Apr 06, 2010 9:45 am 
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djho wrote:
There is no french translation for arc-fault. And I do not know really the difference beetween arc fault and arc flash. Is it a matter of power ?
For sure if they were an arc fault forum, i will post in it !!! But there is no...it is so hard to find people interresting in arc fault and even an arc flash. So it is a real chance for me to talk with you about arc problems.



Arc-fault breakers, measure the current flowing through a circuit breaker and compare it to a known arcing fault profile. The intent is to determine if a low current arcing fault is present and then open the circuit before a fire starts. These breakers are typically used in residential applications.


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PostPosted: Tue Apr 06, 2010 10:56 am 
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lol !! Oh Yes I know what is an arc fault circuit breaker, and this is precisly the topic of my researches !!! The main matter of AFCI is that you need to have the neutral of the line to detect the fault current. In aircraft, if the generator is in the wing, the load may be far from the generator, that implies you need to double the cables. Because of weigth (the major problem of aircrafts systems), solution like fuse topology is prefered.

My question was, if i rewrite, knowing arc fault, how do you define arc flash ? Is an arc flash just a powerfull arc fault ?


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PostPosted: Wed Apr 07, 2010 5:15 am 
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Even though I believe your arcs may not be an arc flash as we know it here, and the parameters are not exactly our normal power system parameters, I feel any discussion of arc physics and research are welcome. We never know what we might learn. I must say your English is better than my French, my French vocabulary is limited to French Fries and French Toast :)

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PostPosted: Wed Apr 07, 2010 12:53 pm 
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Very interesting research.Air will electrically breakdown much easier at higher altitudes.Are you using sphere break-down gap deration curves to estimate these values?

I have included a typical arc flash video link of what this forum group is referring to as an arc flash.It has the ability to instantly kill.Your video is a very very low level arc flash,but it has the ability to crash the airplane controls and kill everyone on board this plane.

http://www.youtube.com/watch?v=UHH4aw-bqwc


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PostPosted: Wed Apr 07, 2010 8:05 pm 
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Its now full circle and it would have been better to introduce the aircraft background in the original post. The forum is dedicated to the discussion of Arc Flash and primarily how that relates to the NFPA70E and IEEE1584 guidelines. Which both are for the benefit of human safety from injuries caused by a severe arc fault, ie, heat, gas, explosion, etc.

Like Jim said, all relative physics regarding arcs are welcomed, and your background to the subject is different, unusual, and interesting.


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PostPosted: Thu Apr 08, 2010 5:45 am 
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I'm actually perfecting my generator with a entirely controlled gap by computer. I can set 10V to 800V for the voltage and i can choose the load i want for serial or parallel arc fault. I can also control the pressure from 1 bar to 0.2 bar. What I want is to plot an abacus of gap for distance and pressure. For the moment I have only do test with sharp electrodes and wires. I have found that the shape of the electrode is an influent factor in determination of the minimum gap distance to breakdown. It is the "sharp" effect (i don't know if it is the right term).
But i never test with spherical electrodes, you advice me to choose spherical electrodes to plot my abacus ?


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PostPosted: Thu Apr 08, 2010 7:53 am 
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Here are a couple of links for humidity and altitude correction factors for different arc gap configurations.Hope this helps. :)



http://www.labplan.ufsc.br/congressos/PowerTech/papers/423.pdf


http://nenki.com/energie_libere/stan_meyer/brevets/Stanley%20Meyers%20hydrogen%20generator/sparkgap_tbl/sparkgap_tbl.xls


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