strange arc appearance / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

strange arc appearance

1 2 next

Move Thread

LAN_403

Dr. Dark Current

Mon Feb 13 2006, 03:15PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

hi, my 1st post there

I was playing with a small DC flyback from old photocopier and noticed something strange (at least for me): when the arc is short (ie 5mm), half of the arc looks "normal" (purple) while the other half (closer to the HV wire) is nearly dark, only with faint blue glow. Just the tip of the HV electrode glows.
The flyback was running at very low power (about 10w).

Attached is a pic of the arc. Sorry for the crappy pic, I took it with my phone

(Yes, the arc in the picture is really an arc / not corona)

HV Enthusiast

Mon Feb 13 2006, 03:31PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Arc can be affected by geometry and/or material of the discharge point. Also, if you were arcing from +HV to GND (RTN), this can affect appearance also.

Without a better photo, its hard to say whats going on.

Dr. Dark Current

Mon Feb 13 2006, 05:27PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

ok I tried o get a better picture but I am really an expert in getting blurry pictures

(with flash it was better but the arc was nearly invisible in the strong flash). I changed both electrodes to copper wire, but it still looks the same.
Here is a link to the pic http://www.volny.cz/jmartis/arc_new.jpg
The red wire is HV from flyback and the white is GND.
(the arc looks blue in the photo but it is actually purple)

HV Enthusiast

Mon Feb 13 2006, 05:45PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

So, you are basically saying you see more corona on one side of the wire, than the other?

Corona does form differently on electrodes depending on which one is more positive. Corona can also take different coloring depending on the polarity as well. This is well documented in many different hv texts including High Voltage Engineering by Kuffel and Zengl.

Dr. Dark Current

Mon Feb 13 2006, 05:59PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

As I said in my first post, it is not corona, but arc. When I open the gap, and start moving the electrodes closer, at first occurs corona (which is assymetrical BTW, and I know it's normal), then sparks start to jump, their frequency increases until they change into continuous silent arc. I'm pretty sure that it is an arc because it can melt plastic and set a paper on fire. That's why I was wondering about it because I saw this effect with DC corona but not arc.

HV Enthusiast

Mon Feb 13 2006, 09:20PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

wrote ...

their frequency increases until they change into continuous silent arc.

Thats normal and i would expect that to happen.

Dr. Dark Current

Mon Feb 13 2006, 09:52PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

EastVoltResearch wrote ...

wrote ...

their frequency increases until they change into continuous silent arc.

Thats normal and i would expect that to happen.

That was not my point, I just want to know why the arc looks so strange (normal purple in one half and nearly invisible in the other).
Sorry, I didn't want this dialog to go so far... 8-o

Sulaiman

Mon Feb 13 2006, 11:14PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I think the arc is vapourising the copper
copper ions are positive
so they will be repeled from the +ve wire into the arc
excited copper ions give Green light.
the negative electrode/wire probably gets blackened with copper-oxide.
Overall bluish light comes from Nitrogen ions.

Dr. Dark Current

Tue Feb 14 2006, 04:06PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Sulaiman wrote ...

I think the arc is vapourising the copper
copper ions are positive
so they will be repeled from the +ve wire into the arc
excited copper ions give Green light.
the negative electrode/wire probably gets blackened with copper-oxide.
Overall bluish light comes from Nitrogen ions.

Hi Sulaiman, thx for your reply,
I've also tried steel wire and aluminium foil, but the arc looks exactly the same, so I think it has nothing to do with the electrode material. I can also take a video of it, but with my skills with a camera, it won't be of very high quality.
I looked closely at the "dark space", and it looks like the arc is wholly transparent here (not even blue).

Electroholic

Fri Feb 17 2006, 03:16AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

I think I know what you are talking about.
My mini marx made the same kind of arc, but it only happens when running at low power.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob