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Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
I thought that this is exactly the reason why we use toroids on our coils?
Field control around the top of the secondary winding, so that sparks don't get tempted to launch off from the wire at the top?
If you put a toroid on top of that secondary connected to the end of the wire, the sparks would have no desire to propagate upwards from the wire because the toroid above would be at the same potential.
Registered Member #1623
Joined: Tue Aug 05 2008, 03:31PM
Location: The Netherlands
Posts: 39
@Herr Zapp The PVC was cleaned afterwards but that was a pretty while ago since I made the coil and never cleaned after that. There was no irregularity in the wire itself, it was just a plain straight piece. The only thing I can come up with now you mention it is that (as you might be able to see at the bottom of the picture) that some of the wire had pieces of polyurethane varnish on it other pieces did not (and it did start at a point were no varnish was). But I can't find any other reason why it decided to break out from that specific point(I still have the piece and I checked it). The strange thing is that around the copper piece of the top the wire was coiled around it and soldered, so I would suspect that the breakout would start there but it didn't.
@GeordieBoy That was my first intuition too, but I wondered why so man other coils I've seen didn't need it and mine apperently did. But thanks to Steve McConner the solution was suprisingly simple.
Many times this occurs as a result of people handling the sec coil without gloves on. Mix your natural sodium salt oils with HV and tracking soon occurs.
Only cure is to sand it complete out, the 2-3 coats of a good HV insulation (I use Dolph's AC-43 to seal all my coilforms).
It's burning the PVC, carburizing it, and the only sure cure is sanding all the carbonization out.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Dr. Resonance wrote ...
Many times this occurs as a result of people handling the sec coil without gloves on. Mix your natural sodium salt oils with HV and tracking soon occurs.
Please tell me this has no effect on the PVC under the coils..I didnt really know that and i did my coils with just my hands on it, no gloves. Would it lead to issues over time where i get arcing under coils? So far all has been good...
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Lots of people have misunderstandings about PVC, especially with the different colors.
First of all, the grey PVC is actually many times a better insulator than the typical "white" PVC you find at your local hardware store. "White" PVC is usually made of either all Type I PVC, or most often, Type I PVC with a central PVC foam core.
Type I PVC Dielectric Strength = 544 V/mil PVC Foam Core Dielectric Strength = 285 V/mil
Now, the "grey" type PVC commonly found in electrical conduit is usually Type II PVC.
Type II PVC Dielectric Strength = 645 V/mil
Also, the "white" PVC is more hygroscopic, meaning it can absorb water more readily than Type II PVC.
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Flashover over secondary PVC
