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Hi Jan,
Your theory and speculations are by no means wild. In fact, I suspect
they're spot on.
Oscilloscope measurements of the E-field around a TC show that ground
strikes almost instantly remove virtually all of the energy that was
previously stored in the ringing secondary:toroid system, while the
lighter load of open air streamers allows the secondary to continue
ringing for quite some time. The brighter appearance and snappier sound
of ground sparks also suggests significantly higher peak current and
higher energy density. These provide supporting evidence that ground
strikes may be high-current capacitor-like discharges. It's also likely
that any high di/dt discharges would shock excite the resulting toroid
and ground path LC system. This is known to occur with Marx generators,
and VDG discharges (per the paper you referenced), so its likely that it
occurs within TC ground discharges.
Jim's suggestion of attempting to estimate the discharge path inductance
or measuring the low-voltage ringing frequencies are excellent ones. You
may also want to try measuring ground discharge current using a wideband
current transformer (CT). The isolation provided by the CT will help to
avoid ground bounce artifacts that can be hard to eliminate during
high-voltage impulse measurements. Also, you may want to try connecting
the grounded side of the measurement gap and measurement resistor to a
grounded metal screen counterpoise beneath the TC. This would help
others to replicate similar measurements in different environments since
the ground path(s) for TC's are often not well-defined or consistent.
Thank you for performing the experiments and sharing them with us!
Bert
jan@xxxxxxxx wrote:
Hi,
I have published another measurement, this time of streamer current impulses
of very high amplitude: