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100kV isolation transformers, high precision voltage and current sensing

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duak:
This fellow has done some HV work with similar voltages: http://boginjr.com/electronics/hv/multiplier/  I can't vouch for the long term reliability but the concepts are sound.  His website has various other tidbits.

A lot of the nuclear research facilities such as CERN, Fermilab and SLAC work with EHV and have published papers on the equipment designed and built there.

Cheers,

Spirit532:
Whoa, lots of replies.


--- Quote from: jbb on February 11, 2019, 06:42:08 am ---It’s unusual, but have you considered PCB windings for the transformer secondary?

--- End quote ---
Usable up to ~20kV tops from my experience, and a bit of a mess to make, especially for higher power.


--- Quote from: Berni on February 11, 2019, 07:11:33 am ---What you need in my opinion is a massive ferrite C core.

--- End quote ---
Doing exactly this - 20mm separation on either side, 40mm ID C-core.


--- Quote from: Berni on February 11, 2019, 07:11:33 am ---As for the HV side sensing circuitry you can simply have an extra winding to create a supply voltage for it and treat the -100kV as being ground, this lets you use normal opamps up there to sense all those parameters you want. Tho i would recommend putting the elctronics in a shielded box that's also connected to -100kV to protect the circuitry from any potentially very strong fields drawn to anything grounded.

--- End quote ---
The high voltage PSU is very low power(calculated to be 8W input), and the HV transformer itself is only good to ~15kV. The rest is going through a 5-stage CW multiplier. This is why I'm doing a separate -HV filament supply.


--- Quote from: Doctorandus_P on February 11, 2019, 01:48:29 pm ---a toroidal transformer with a diameter of around 40cm

--- End quote ---
That is gigantic for my application - the entire system will probably be thinner than that, and definitely shorter.


--- Quote from: NiHaoMike on February 11, 2019, 02:00:59 pm ---Have you considered a BLDC motor driving another through a plastic rod?

--- End quote ---
That is a crutch even I won't consider, and I've done some pretty hacky stuff. Fairly easy to implement, but a bit nuts to add mechanical transmission of power. That, and you can't pot it.


--- Quote from: MasterTech on February 12, 2019, 02:50:59 am ---That is going to be a mess, silicone is not free flowing so its not that easy to vacuum pot, especially with weirded shapes like transformers. Anyway why would you want to pot a research module like that, you will not be able to make repairs, change things or study potential problems.

--- End quote ---
I have some low viscosity 2-component HV silicone that will work great for potting. It's not going to be an extremely tight assembly, so penetration won't be an issue. I might also be potting under vacuum, with air ingest to push it as far as possible.
This isn't a research module - I'm intending this as a part to go into an assembly that will sit inside an x-ray microtomograph. It will never be taken apart or serviced.
Oil is really messy to work with, and potting gives me standalone modules I can mount in air, rather than having to design and build enclosures and passthroughs for every cable. That, and as you've mentioned, it needs to be very dry, which is hard to achieve without using drying agents or buying brand new oil.


--- Quote from: blueskull on February 12, 2019, 03:18:00 am ---There is a Taiwanese company making up to 0.5W (recovered electrical power) per channel laser fiber power delivery systems.

--- End quote ---
Nope. The filament needs ~5.5W peak, + regulation losses.


--- Quote from: djacobow on February 12, 2019, 04:52:23 am ---I do have one question, though: how does the tube know what potential it's at?

--- End quote ---
It doesn't. You need a regulated HV power supply to get the x-ray energy you want. In my case it's a beryllium window tube, so anything from ~10kV and up will output x-rays, though 10keV won't do much other than photoionize surfaces.


--- Quote from: mjs on February 12, 2019, 07:44:07 am ---How much do you have to pay for the modules and how much power do you get through?

--- End quote ---
Not a lot, and see above for power.


--- Quote from: jbb on February 12, 2019, 10:29:49 am ---It’s totally out of scope, but now I’m imagining an X Ray tube that replaces the filament with fibre fed laser heating. After all, converting laser light to electricity to run a heater is very inefficient.

--- End quote ---
It could work - just have to set up a high vacuum glass-to-metal and beryllium window production line first. Quick, patent it!
Filaments burning out is a very large part of why X-ray tubes die in general, so if you eliminate that, they could last a very long time.

Designing a compact HV source with isolated filament supply is quite a weird combination, considering basically no modern microfocus x-ray tube uses a grounded anode setup, because as you can see, complications arise.
Grounding the anode lets you leave the focusing voltage regulation to the tube itself(via a resistor to the "grid"), but modern electronics have gotten good enough to generate the focusing voltages externally. Kevex tubes are a nice example of that - the tubes are ridiculously long and there's a whole braid of cables coming off the anode.

Yansi:
Not sure why you have not reacted on my suggestion of winding a couple turns secondary to get the floating filament supply.

But, you should give it a try, I am pretty sure it might satisfy your needs of being quite compact in size. (bulkness defined mostly by how thin of a high voltage insulated wire you can get).

Not sure about 100kV+ rated wires, but those readily available 40kV ones are pretty thin and couple of turns would not be much of a challenge within a small core, such as ETD34 or a 3cm toroid.

Spirit532:

--- Quote from: Yansi on February 12, 2019, 09:29:42 pm ---Not sure why you have not reacted on my suggestion of winding a couple turns secondary to get the floating filament supply.

--- End quote ---

It's mentioned in my previous reply - because I'm winding a separate transformer for the HV supply. The main HV transformer will be very low power, and I'd rather not triple the HV system's input power and make the driver circuit more complex.
That, and the HV transformer is going to be at +9kV(max, accounting for CW losses), while the CW output will be at -100kV.

jbb:

--- Quote from: Spirit532 on February 12, 2019, 09:23:10 pm ---
--- Quote from: jbb on February 11, 2019, 06:42:08 am ---It’s unusual, but have you considered PCB windings for the transformer secondary?

--- End quote ---
Usable up to ~20kV tops from my experience, and a bit of a mess to make, especially for higher power.

--- End quote ---

Sorry, wasn't clear; I meant just doing the primary and secondary as PCB windings on separate boards, then potting the void between them.
I'm impressed that ~20kV is possible with both windings on one PCB!


--- Quote from: Spirit532 on February 12, 2019, 09:23:10 pm ---
--- Quote from: jbb on February 12, 2019, 10:29:49 am ---It’s totally out of scope, but now I’m imagining an X Ray tube that replaces the filament with fibre fed laser heating. After all, converting laser light to electricity to run a heater is very inefficient.

--- End quote ---
It could work - just have to set up a high vacuum glass-to-metal and beryllium window production line first. Quick, patent it!
Filaments burning out is a very large part of why X-ray tubes die in general, so if you eliminate that, they could last a very long time.

--- End quote ---
Forgive my ignorance; I though X-Ray tubes are largely made of glass.  I've never worked with them myself (and might be too chicken given high V and radiation hazards I'm not trained for).

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