Steve Ward wrote:
Hi Dex, Glad you could chip in here a bit, i was having trouble finding any good references for coils with discharges much longer than the top voltage would suggest. More comments
I suspect that most coils are in this category. at 30kV/cm, 200-300kV (which is probably a typical topload voltage for a small NST coil) would only support a spark of 7-10cm, and sparks much longer than that are common.
The difficulty is multifold:The field is very non-uniform, which tends to lead to longer sparks, even in a single shot environment (Bazelyan and Raizer's book talks about this a lot, in connection with EHV and UHV transmission systems and switchgear)
you have multiple pulses which can successively extend the spark through a previously ionized channel.
As an obvious indication of unusual behavior, a lot of coils have sparks longer than the distance from topload to base, without arcing over the secondary coilform.
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