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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843
Has anyone ever used any TDK UHV-series caps in an application where they were run at a significantly higher voltage than their rated voltage? And if so were there any problems?
As many papers on Marx generators that I've looked at, it was only recently that I realized that the company "Aplec" seems to be running their TDK ceramic caps at a significantly higher voltage that the spec.
For example, in the paper "A MODULAR COMPACT MARX GENERATOR DESIGN FOR THE GATLING MARX GENERATOR SYSTEM", a marx generator is described which uses TDK UHV-4A capacitors (30 kv, 940 pf) at a maximum charge voltage of 40 kv; a 33.3% over-voltage.
According to the authors: "The capacitors are rated at 30 kV, but have proven to operate thousands of shots at 40 kV without risk of failure."
I can see that the pressurized gas inside the Marx generator would likely present flashover, but the other possible limiting effect might be low efficiency/high power dissipation. But then when I was researching that possibility, I came across the paper "Capacitor Evaluation for Compact HV Pulse Generation"
And from this paper it seems like you would suffer a loss of efficiency, but even at a 50% over-voltage (1.5*Vr), the efficiency only drops to 93% (vs 99% @ Vr).
According to the TDK data sheet, these UHV-series caps will apparently withstand a 50% over-voltage for (60 seconds at least), while under oil, but I wonder if there's any general rule of thumb as to how high you can go in air with these caps before they flash over?
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I guess if I want to know approximately where a UHV-12a cap will flash over in air, I'll have to do some of my own testing.
My main problem is that I have a rather small work area, and right now it's cluttered with other projects, e.g., a vacuum system I'm working on. But in the meantime I'd nevertheless like to be thinking about and simulating the HV pulser.
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Over-volting TDK Ceramic Doorknob Capacitors
