[coryrc]

> The expensive part used to be the voltage conversion stations at the ends, but with mass production of MOSFETs for EV's these have now become far cheaper than the JFET's and other exotic silicon that used to be used.

Why do you believe these things are related?

HVDC lines operate in the hundreds-of-kilovolts range. For example, https://en.wikipedia.org/wiki/Basslink operates at 400kV. There are no MOSFETs or JFETs directly involved in stepping down that power.

[londons_explore]

Semiconductors are stackable to get higher voltage. They're parallelizable for more current. Cost scales linearly with voltage and current, and is therefore constant WRT to system power.

[tim333]

Apparently they use thyristors https://en.wikipedia.org/wiki/Thyristor#HVDC_electricity_tra...

https://en.wikipedia.org/wiki/HVDC_converter#Thyristor_valve...

[londons_explore]

Thyristors require you have at least one transformer operate at AC line frequency (50/60Hz). That costs a lot, since you need enough steel to store 20 milliseconds of your total power as a magnetic field. Thyristors are on-off devices (like most semiconductors when used for power conversion), but cannot turn off without zero current, which precludes a bunch of high frequency designs which are better for harmonics and weight-of-steel.

Overall, they were a popular choice in the 90's and 2010's, but I don't think we'll see any new designs installed with them.

[tim333]

Ah - right you are. Seems IGBTs are the thing now.

[coryrc]

I've never heard of MOSFETs being used in extra-high voltage systems, but I have not been following the industry for a while. Do you have any links? I've only seen IGBTs or older technology used.