Hi Herwig,The voltage across the MOT itself is due to the cap value (hope were talking apples and apples and the same Piranha circuit). The resonant value for the MOT was near 1.45uF, so the MOT and total capacitance (2x330nF) is operating in STR at 1/2 it's Cres value. Considering the current source of the MOT and depending on the SISG's switching rate, it can get to 4kV in steady state. But again, how fast it charges the caps between switching is something that must be looked at in the simulations which needs a Sidac-IGBT type part in the model.
In Terry's Piranha 3 (.sch file), I noticed he set up what appears to be a modeled circuit for this, but my Microsim is either too old or he built a custom part in a library that I don't have. He may have been operating on v9.1 at this time (not sure). In any event, you want a voltage controlled switch that switches at the Sidac series voltage based on the MOT current and caps charging rate (ideally). Easier to say that it is to actually set up. This is what I think needs to be setup in order to "accurately" simulate the circuit as a whole (and of course to insert the coil load itself). I really wish I had my old computer right now where all my Microsim files were stored (seems I'm reinventing the wheel once again).
Ferro-resonance is certainly a possibility. I feel pretty confident there are moments, but I'm not sure how it fairs overall. I wonder if simulators are accounting for ferro-resonance? Considering there are specifically designed ferro-resonance transformers with added C for voltage regulation, current limiting, constant current source, etc., it seems logical that simulators should be taking this into account.
Regarding the MOV's: If their getting hot within seconds, then their switching all the time. Are you using MOV's across the MOT's secondary winding? If so, what are is the rated turn on voltage?
Take care, Bart Herwig Roscher wrote:
- of course 2232*sqrt2*2 = 6313 Vpp. I was not writing about the voltage across the capacitors but the voltage across the MOT and I wanted to know the source of this voltage rise. Two possibilities come to mind: emf and ferro-resonance (thank you for mentioning). This overvoltage ruined my medical HV tranny. Using MOVs across the MOT is no solution as they become blazing hot within seconds. I am afraid of connecting a capacitor across the MOT as it could produce new resonances. And I do not dare to use my oscilloscope close to a running TC of course.
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