Hello Steve,
The damage to the secondary was actually surprisingly limited with two small (about 3mm diam) charred areas corresponding to the violent flashes on the video and perhaps three or four pinhead burns. As far as I can tell, no fused turns but the subsequent 'shorted turn ' phenomena I think was the carbonising at the areas, this was also limited in scope. The winding had many coats of Dolph's AC43 which may have been partially protective but obviously unable to withstand the strike. As Phil T mentioned, I think over coupling can be ruled out since it was lowered from 0.14k this time from 0.12k last year and an almost identical flashover happened on that occasion. The coil is rather under toroided relative to the 12" sec diameter but this cannot be resolved for a few months. The same 50" diam fabricated toroid we use on Phil T's 8" SRSG coil running at the same power is highly protective, his secondary never suffering this kind of damage.
Regards,Phil S.
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14 Broad Street, Stamford, Lincs PE9 1PG
Tel: 01780 753008
On Wednesday, 4 July 2018 19:02:44 BST, Steve White <steve.white1@xxxxxxxxx> wrote:
Hello Phil,
Ouch! That strike looked really destructive, as in much more than a few damaged secondary turns. At an operating power of 4.8 KVA, I have had a few brief strikes to my secondary with no apparent damage, but nothing like this. I wish we could all figure out a way to prevent these but there probably isn't a way with these power levels.
Steve
----- Original Message -----
From: "phil" <pip@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Sent: Wednesday, July 4, 2018 8:48:19 AM
Subject: [TCML] Bad strike to a 12 inch traditional coil (somewhat terminal)
Gents & Lassies
Slightly odd one, with a video at: https://youtu.be/tcESWWbcr7I
This recently occurred to Phil S's 12 inch coil that on the day in
question, and also the previous day, had ran fine. Tuning had been done
with an oscilloscope, and the coil was not considered over-coupled. The
winding had though sustained previous damage which had been repaired a
year previously, however this latest damage did not appear to align with
where the previous splice had been done, and as mentioned, it had
already had some higher power runs that day.
As you will see there was already a streamer strike "in progress" (so as
to speak) from the toroid down to the primary strike-ring when the 1st
secondary flash-over up the winding occurs. This finished around 30m/s+
later and then a second flash-over occurs fairly soon after.
This time however the ongoing toroid-to-strike-ring streamer (which had
started 0.5 second or so before the 1st flash-over) now forks over to
join the secondary flash-over. Then the fun really begins!
Were these flash-overs a result of the initial strike to the
strike-ring, or just coincidence?
Initial thoughts were it looked like so called 'racing sparks', but they
did not initially extend up the winding very far, so jury is still out.
Coil is 100 bps SRSG using a phase controller.
Phil T
(Luddite Coiler UK)
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