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Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I'm in the process of upgrading my first SSTC. I wound a new primary on a plastic plant pot for maximal coupling, but now I'm suffering from constant primary flashovers. I've had to lift the secondary nearly out of the primary to stop it. What I find odd is that the arc-overs don't seem to be initiated by a secondary strike, but rather directly between two primary windings. I placed a few overhead transparencies around the secondary, and after another arc-over I examined them to find the only damage to be caused by the flashover heat. I'm using a DC-blocking cap of 680nF and primary inductance of 30µH, so resonance isn't a problem. Is it the E-field from the secondary that's the problem? Helping the low primary voltage jump through it's insulation? I think I read that using a plastic sheet placed 90 degrees (horizontally) to the secondary would cut the E-field, might this help?
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
I was have this same problem with one of my SSTC's, when the primary turns is near the middle of the secondary coil, the Potential Energy field grows, so the chances of primary-secondary flashover grow too. I solved the problem reduncing the spaces between the turns, and insulating the secondary coil with a PVC Plastic Sheet (0,27mm) and insulation tape. It worked, but not a nice visual.
Maybe the plastic sheet that you have put help, I dont know. You must try.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I tried a plastic sheet (four actually) all the way up to the topload, but it didn't help. Poorly explained in my previous post was that after one arc-over with the sheets, I examined them to find no signs of puncture from a streamer or arc. The arcs seem to initiate between the primary windings themselves!
Fixed! I used one of the transparencies as an "E-field cutter" if that's what it really does. At any rate I was able to lower the secondary a notch with just one sheet. I'll buff it up and optimize it tomorrow. I also noticed an awesome deep blue from my nearby halogen desk lamp. The direct hit from a streamer is coincidental.
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Primary flash-overs on SSTC upgrade
