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Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
I am aware that chemical elements (Strontium & Barium) & metals (Copper, etc) can affect an arc's colouration. But why do some arcs appear to be burning as a low oxygenated flame (like a match) and others are high in UV & crisp? I have noticed that current levels do not always result in one or another; there appears to be other factors involved. Can anyone shed some light (sorry, that was bad) on the variances of arcs, their structure and appearance?
What little experimentation I have done has resulted in no conclusive extrapolations. I live in Southern Arizona were I have days with virtually no humidity and Monsoon with a GREAT deal of humidity. There is opportunities for dust in the air and very clear days. Therefore I have a setting for a variety of experiments. I am a welder and have seen a great deal of high current arcs, however when I see some MOT's drawing arcs that have a good amount of current, they also differ in structure & appearance.
Registered Member #1339
Joined: Wed Feb 20 2008, 04:43PM
Location:
Posts: 9
Quick,
There are several references to this phenomena in PEEK's "Dielectric Phenomena in High Voltage Engineering" about different characteristics of corona and arcs based on the polarity with respect to "ground" This may shed some (no I'm not gonna do it) on your question. You can get a PDF version of this book at
Everyone should own a copy of this masterpiece of high voltage work.
I have noticed that current limited arcs seem much more in the UV emmision, but have seen pinkish glow as well. This was with copper electrodes (sharp points) from a flyback type. Could be related to frequency as well ???
Registered Member #1381
Joined: Fri Mar 07 2008, 05:24PM
Location: Hungary
Posts: 74
Basicaly it all depeneds from the applied Frequency and Power (in cw) Every arc can be understood as really "cold" and "sparse" plasma So the ions in the channel are not very stable cause the temperature is just a few eV , so the charge varies , then again if your are not pumping in kWs theres not much current (magnetic field) to "hold" the plasma the "Gas pressure" will be equal to "Magnetic pressure" via lens/lorentz force (so the hotter the more unstable it will become) ,this is why plasmas/arcs are unstable and behave chaoticly ( the simple answer :P)
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
Things I know of that affect arc appearance are:
1. The arcing atmosphere (gas) 2. Atmospheric pressure 3. Electrode materials 4. Electrode geometry 5. Current level 6. Current density 7. AC frequency 8. Rise and fall times of the AC envelope
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
Fredrick wrote ...
PEEK's "Dielectric Phenomena in High Voltage Engineering"
I had to poke about a bit but I found the book and it looks great!! I really like reading about any hobby as much as I love to experiment.
I have been experimenting with both AC & DC and the enormity of the variances are impressive. I find that I can get an arc to be visually different MUCH easier than I can to get them to appear the same!
The answers, thus far have opened up a whole world of concepts and ideas. I imagine many of you must work within EE or related fields. (The puns just keep on coming with these subjects...sorry)
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Why Do Arcs Differ?
