Hello,

a few years ago i build a QCW coil, but never finished the project completely.
This week I want to finish the project.

Short description of the coil:
* h-bride with 8 x FGH75T65SHD-F155
* V_bus: rectified 230V AC mains = 320-350 V DC
* Upper pole of the combination betteen primary and secondary: 406 kHz with a drop of about 30 kHz during spark growth
* Primary capacitor: 12.4 nF / 10 kV
* Peak primary current: 160 A
* Ramp form 20 % to 80 % of V_bus via phase-shift-modulation
* Ramp rise time 10 - 20 ms
* Ramp fall time 1 - 4 ms
* Ramp wick time 3 ms at 20 % (flat period prior rising ramp)
* Pointy Tungsten electrode as breakout point
* JavaTC file as attachment

The coil is running very well with nice straight sparks (approx. 160 cm), but only at bus voltages of around 250 V. If I crank up the voltage to the full 340 V, flashovers between primary and secondary coil are present (even with a ramp from 20 to 50% and 20 ms ramp rise time).

I measured the field with a nearby oscilloscope probe. The flashover occurs at around 3/4 of the ramp. It feels as if the spark at the top of the coil can not break out and therefore the voltage at the top of the coil rises to much.

Do you have any ideas? Should I reduce the coupling (calculated 0.391)?

Greetings
Gerd

Hello,
does somebody have access to a (perhaps broken one) rogowski current probe for use with an oscilloscope?
I cannot find any pictures from the inside of such a probe (integrator part of the probe) anywhere in the internet.
I would be very happy if someone can open a probe and take some pictures.