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[TCML] Re: HV psu

On 2/7/23 9:08 PM, Ian Gault wrote:

    I’m interested in replicating David LaPoint’s ‘Primer Fusion’ project.

    This is my first plasma project. I have been working with high voltage
    impulses up to 7kV regularly, but am asking advice on the best way to
    build a psu providing ~500,000v.

That's quite a challenge, mostly from the mechanical side - insulating 500kV is not easy, especially things like avoiding corona.

in air, uniform field breakdown is around 30kV/cm (70 kV/inch) (round numbers), but the field isn't uniform on most HV gear.

All your conductors need to have big radii of curvature. Immersing in oil or SF6 helps a fair amount, but brings with it a bunch of other difficulties (leaks, mess, etc.)

    I plan to use a Cockroft Walton multiplier in 20-30kV steps, but need a
    psu to provide 20-30kv to the first stage.

Yes, that works - Take a look at the C-W generator pictures in museums (there's a nice one at the Scottish National Museum in Edinburgh)


that's 1 MV and fairly old technology for the HV rectifiers, but it is air insulated, and gives you an idea of the size needed to get insulation.

Tesla coils get up to around 500kV, but you'll note they generate copious ozone (indicating corona) and, of course, have sparks into free space.

    The main difficulty I’m having is that I want to be able to manipulate

    1 – Voltage 0-500Kv

Varying 0-500kV with a single knob is possible, but more likely you'd do it with various taps (add/remove parts of your CW stack, for instance)

    2 – Phase
The CW is a DC output device, maybe what you want is a cascade transformer?

    3 –  Polarity
You can reverse the rectifiers in a CW and flip the polarity. Not with a switch, but more like by restacking it.

    4 – Frequency

What range?

    5 – Duty (possibly)

    This would require amplifying the input signal without altering its

that's really, really hard.

You didn't mention what current you need.  Microamps? Milliamps?

    It looks like ZVS into Flyback tx’rs will only work on specific
    frequencies, so could a NST work?

A NST will do a nice job of getting you ~15kVrms from line voltage, with some limitations.  you could drive it with variable voltage and frequency (within limits).

    I plan to use an existing system I have with dual channel signal
    generator to control freq, phase, and duty into dual gate drivers/HV
    Mosfets for impulses, but also require a continuous power feed as an

If you're doing AC, then a cascade of transformers might be a way to get what you need.  The classic way is to have transformers with multiple windings and really good insulation. Say you want 500kV.  If you have 5 transformers that have 100kV output (and insulation to match), you run them in series.  The trick is how do you get primary power to the transformers at the top of the stack?  Say your transformers are 20:1, 5kV in and 100 kV out. The bottom transformer has 3 windings, 2 for 5 kV, and one for 100kV.  One of the 5kV windings is insulated for 100kV.  You feed the low voltage 5kV, take the higher insulation voltage 5kV and feed it to the next transformer up the stack, which sits at 100kV above ground potential.

https://top10electrical.blogspot.com/2014/11/cascaded-transformers-method-for.html has a nice picture.

    Any advice would be greatly appreciated.

    Many thanks,


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