| Electronics > Projects, Designs, and Technical Stuff |
| 100kV isolation transformers, high precision voltage and current sensing |
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| PartialDischarge:
--- Quote from: Spirit532 on February 10, 2019, 09:06:46 pm --- --- Quote from: David Hess on February 09, 2019, 03:30:52 am ---I would just monitor the current on the primary side of the transformer. I might also use several transformer cores in series with balancing to get the required high voltage isolation. Were you planning on vacuum potting? I sure would. --- End quote --- I'm definitely doing vacuum potting in high purity silicone designed for isolation. It has a minimum guaranteed dielectric strength of 25kV/mm at 20C and 60% RH, I'm going with 15-18 mm on all sides of the HV winding - though obviously it's not going to be good for 400kV, but it should be fine below 100kV. --- End quote --- 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. Use transformer oil, just need to be dry and by dry I mean less than 0.01% water content. Good transformer oil withstands more than 35kv/mm. Paraffin oil is a good alternative, from the environmental and safety points of view, but again needs to be very dry. But dielectric strength doesn’t mean that much. You need to study the relative conductivities and permittivities of the materials inside the tank. At dc conductivity is what matters, and permittivities at ac. The electric field and equipotential lines will distribute accordingly and in a very savvy way. Thats why in practice mixed insulating materials are used in high voltage tanks, solid insulators and oil, one is good where the other isn’t. Their distribution and width matters cause you are creating capacitor dividers (and resistive dividers at the same time) inside. For example if you place a sheet of insulating plastic around the xray crystal tube with high er, you will probably create arcing since now the tube ampule forms a capacitor with smaller value than the sheet |
| djacobow:
I have nothing to add to this thread, but it has been interesting to read. I have never dealt with these sorts of problems. I do have one question, though: how does the tube know what potential it's at? |
| mjs:
How much do you have to pay for the modules and how much power do you get through ? I did a proof of concept by just plugging a 1W laser diode to 1mm PMMA fiber end and easily got the 10mW/3.3V I needed. That's not suitable to any kind of real use, so I'm looking for commercial components to focus on the actual measurement electronics next. |
| jbb:
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. But for practical use I’d stick with isolating transfomer. |
| Yansi:
I do not see much issues here. Just grab a large enough ferrite core, wind a secondary with high voltage cable to obtain those few volts to run the filament and measurement circuitry. Use a cheap multimode optical fiber for the feedback. I don't think you could do much simpler than that. Not sure why everyone is recommending some ultra expensive complex solutions as some laser powered modules. No special transformers required, no thick bobins to be turned on a lathe. Just grab an off the shelf ferrite core, and a length of a high voltage insulated cable. //EDIT: Just thoughts for the filament supply plus the measurement circuitry isolated supply. Generating the -100kV is another matter I have unofortnately not much experience with. |
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