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---------- These aren't breakers and aren't meant to interrupt current- they are isolating switches. If one attempted to use one to clear a fault- then there would be real fireworks (and likely destruction of the switch without clearing- opening on normal load current is also not recommended but spectacular). The breakers have contacts completely enclosed (no fireworks unless it explodes) and use forced oil, pressurized air or Sulphur Hexafluoride and can be quite compact. In these the gaps are fairly small. The idea is to build up pressure which is held back by the arc plasma and when this dies at current zero- replace it with good dielectric by blasting air, oil or SF8 through a few fairly small series gaps of the order of 1 inch ( a 1950's air breaker operated at 400psi and 161KV had 4 gaps of the order of 1 inch each). With an air breaker, there is a big bang but no fireworks. The others are quieter. Breakers are fascinating as at high voltage brute force opening of a switch is simply not adequate. A movie made may years ago showed a test where a grounded wire was thrown across a 230KV line. The wire vaporised and the arc wandered all over the place-extending 30 ft before it was quenched.
---------- They don't have breakers on the DC side but can gate off the thyristors so that when the supply current goes to 0, the thyristor leg stops conducting in order to kill a fault quickly. There will be breakers on both AC sides. There have been many attempts to make HV DC breakers but so far the results have been poor- Basically they use an AC breaker and with a lot of added complications superimpose an AC current across the breaker contacts to force current zeros. This has been found to be very expensive. With AC, the effectiveness of the breakers means that one can have a network but with DC, that is out of the question and even a T connection may involve 3 rectifier/inverters "back to back". So DC is point to point long distance bulk transfer or ties between two systems which may be at different frequencies (or not connected by AC for stability reasons) or for long underwater cables. Economics of DC vs AC favor these applications and the ease of voltage level optimisation with transformers is available only with AC
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-- look at a 765KV substation some time-Take your binoculars. Do it in a "wet" snow storm and start estimating the distance from the hot end to where you are and the distance from you to where the insulator is "winking".