Comment by tlb
1 day ago
It's true that you can switch very high voltages with MOSFETs in series. But the next step after switching is a transformer that needs to handle 14 MV between the primary and lower-voltage secondary winding. I don't think anyone has built something like that before. Given the dielectric strength of transformer oil, the primary windings need to be 500mm away from both the secondary windings and the core, which seems like it'd be hard to do while getting good inductive coupling.
35mm of silica glass would do the trick.
Since the ferrite core isn't a good insulator, the glass would need to fully encase either the primary or secondary winding.
At the sort of scales this transformer would likely be built, an extra 35mm would make the whole thing a little bigger and more expensive, but not massively so.
The glass tank could also double up as an oil bath for cooling the coil - the first 500 millimeters or so of the piping needs to be glass, but after that you can use a typical cooling radiator with no extra concerns.
Nah, just do a few divide-by-2 capacitive converter stages to tame it. Basically just a FC-3L buck running at exactly half to not need meaningful amounts of inductance. Feed the radiation to adjacent phases of a radially symmetric setup, and it shouldn't be an issue anymore.
These classic HVDC transformers only exist because those lines plug directly into the AC grid; it's easier to just tame the HVDC and keep it DC for a bit, though, at these extreme facility sizes.