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A Compact 3 MV Transformer

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jpsmith123

Fri Jul 31 2009, 05:57AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Speaking of HV transformers, I came across this paper:

In addition to the remarkably small size of the unit, what's interesting is that the output voltage was apparently limited to 3 MV by periodic breakdown in the load circuit (the water capacitor), not in the transformer. And the author (Rohwein) states that if not for the breakdowns, he would've taken it to even higher voltages...implying a conservative design.

When I saw that the layer insulation was so heavy (8 layers of 0.019 cm mylar), my first thought was that the transformer was over-designed, yet the as-built coupling coefficient was still 0.83, which exceeds the desired 0.6 value for efficient double resonance operation. So it apparently could've had more turns or even more insulation.

Yet as far as the insulation thickness of 1.52 mm per layer, well, the pulse transformer in the below linked example had only 0.6 mm per layer, less than half that of Rohwein's transformer, yet the authors felt it was good for several hundred kv.

If this is correct then I would speculate that Rohwein's basic transformer design might be useable to 6 MV or even higher.

Maybe this type of transformer might be useful to drive a home-made pulsed electron accelerator?

HV Enthusiast

Fri Jul 31 2009, 12:57PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Thats a pulse transformer, not a transformer rated for continuous output. Huge difference. This transformer (or rather the whole system) is an alternative to a Marx Generator (single-shot output pulse) not one to a continous output high voltage transformer.

Also, the input to the transformer is a pretty complex pulse forming network which requires its own 50kV input on the primary.

All in all, this needs to be compared to a similarily sized 3MV marx generator with the same energy output and the system size comparison should include all the supporting circuitry including the massive 4.6kJ 50kV capacitor charging network which is used to drive the primary on the transformer.

This is not a transformer where you simply connect to a full-bridge input and get 3MV on the output.

jpsmith123

Fri Jul 31 2009, 03:22PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Dr. GigaVolt wrote ...

Thats a pulse transformer, not a transformer rated for continuous output. Huge difference.

Firstly, for various technical reasons, I would put the "pulse" part of that in quotes; IOW, it's apparently not a pulse transformer in the sense that it was not designed to efficiently reproduce a voltage amplified replica of an input pulse (as the coupling coefficient would seem to be too low), nor is it limited by a volt-second product. Rather, I tend to see it more accurately described as a dual resonance transformer operated in a pulsed mode.

Second, although obviously intended for "pulsed operation" (and I don't think any kind of duty cycle was mentioned), strictly speaking, there's no fundamental reason why this transformer coudn't be operated in a "CW mode" under the right conditions. Other than the fact that we don't know what kind of average power throughput the device could handle without burning up (regardless of "CW" or "pulsed" mode), nor do we know if or how much the voltage hold-off of the insulating system would have to be derated, what "huge difference" do you see?

wrote ...

This transformer (or rather the whole system) is an alternative to a Marx Generator (single-shot output pulse) not one to a continous output high voltage transformer.

I didn't necessarily mean to imply anything different.

wrote ...

Also, the input to the transformer is a pretty complex pulse forming network which requires its own 50kV input on the primary.

But for the fact of the somewhat too high as-built coupling factor (which required some external inductive compensation), being simply a dual resonant transformer operating in pulsed mode, it requires a capacitor and a spark gap. How's that "complex"?

wrote ...

All in all, this needs to be compared to a similarily sized 3MV marx generator with the same energy output and the system size comparison should include all the supporting circuitry including the massive 4.6kJ 50kV capacitor charging network which is used to drive the primary on the transformer.

Indeed. And once you do that, you'll see why I used the term "remarkable".

For example, here's a 1.6 MV (open circuit) 850 kv (50 ohms) Marx generator capable of a whopping 260 J, built by a company "APELC" which refers to itself as "the world leader in the development of compact Marx generators". So their products probably make for a fair comparison.

This Marx generator, apparently their most powerful unit, has only about 6% of the energy throughput at about 28% of the load voltage; yet it's 6 ft long, 9 inches in diameter and weighs over 250 lbs.

wrote ...

This is not a transformer where you simply connect to a full-bridge input and get 3MV on the output.

I hope nothing I said can be construed as an inference that I believe you can hook the mains up to this thing through some mosfets and get 3 MV out. If so, I apologize for being so misleading. It's merely something I came across while doing some research, and I thought others here might find it as interesting as I did.

That said, according to some stuff I've seen, loosely coupled air core transformers can apparently be part of a practical HV switching power supply, see, e.g., US Patent 6934165.

Steve Conner

Fri Jul 31 2009, 04:07PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

It's an odd-shaped Tesla coil. End of story.

By the time you add the primary capacitor bank, spark gap and charging supply, 6 ft 9" and 250lbs sounds about right.

I knew people at Strathclyde University who made compact oil-insulated Marx banks up to 1MV and 4kJ. They were "only" about the size of a fridge.

I. C. Sumerville, "A Simple Compact 1 MV, 4 kJ Marx", Proceedings of the Pulsed Power Conference, Monterey, California, Jun. 11-24, 1989, No. conf. 7, Jun. 11, 1989, pp. 744â€“746, XP000138799.

jpsmith123

Fri Jul 31 2009, 04:50PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Steve McConner wrote ...

It's an odd-shaped Tesla coil. End of story.

Basically, yes.

wrote ...

By the time you add the primary capacitor bank, spark gap and charging supply, 6 ft 9" and 250lbs sounds about right.

I knew people at Strathclyde University who made compact oil-insulated Marx banks up to 1MV and 4kJ. They were "only" about the size of a fridge.

In my view, when you add it all up and compare size, weight, cost, complexity and efficiency, for a given voltage and energy output, I think the "pulse transformer" beats the Marx generator hands down, but that's only my opinion.

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