4 ms·

HVDC is becoming more common for medium and long distance transmission lines because HVDC doesn't suffer from the "skin effect" where current is carried mostly

HVDC is becoming more common for medium and long distance transmission lines because HVDC doesn't suffer from the "skin effect" where current is carried mostly by the outside of the conductor, and therefore you can transmit more power with less conductor with HVDC. The tradeoff is, it's much easier to step up and step down AC voltage (using solid state transformers)

bsder 9y ago
True, but none of this has changed recently. The recent change is the fact that high-voltage semiconductors now make step-up/step-down efficient. In many cases, more efficient than purely using transformers (most semiconductor stuff still uses some form of inductive effect--they just do so at MUCH higher frequencies than in the past which allows them to use MUCH smaller components and get much higher efficiencies). One of the big advantages of AC has to do with switching. If you flip a switch on AC, within about 10 milliseconds the voltage goes to zero as a natural consequence of the waveform irrespective of what current was flowing previously. A switch can interrupt that without much grief. If you flip a switch on DC, it has to completely stop the current flow in the presence of a large current and/or voltage that will create a conductive plasma. That means a much larger switch for the same level of power. There is a reason why your ISP has a huge switch and it is often encased in some inert gas. And also why it sounds like a bomb going off if it trips. And why it takes a hydraulic pump to reset. Side note: The Pacific DC Intertie was the largest in the world until the 3 Gorges Dam interties--and it dated to the Kennedy administration and used vacuum tubes. https://en.wikipedia.org/wiki/Pacific_DC_Intertie https://en.wikipedia.org/wiki/Pacific_DC_Intertie
- jerkstate 9y ago
  Cool, thanks for the additional info. TIL!

bsder 9y ago

True, but none of this has changed recently. The recent change is the fact that high-voltage semiconductors now make step-up/step-down efficient. In many cases, more efficient than purely using transformers (most semiconductor stuff still uses some form of inductive effect--they just do so at MUCH higher frequencies than in the past which allows them to use MUCH smaller components and get much higher efficiencies). One of the big advantages of AC has to do with switching. If you flip a switch on AC, within about 10 milliseconds the voltage goes to zero as a natural consequence of the waveform irrespective of what current was flowing previously. A switch can interrupt that without much grief. If you flip a switch on DC, it has to completely stop the current flow in the presence of a large current and/or voltage that will create a conductive plasma. That means a much larger switch for the same level of power. There is a reason why your ISP has a huge switch and it is often encased in some inert gas. And also why it sounds like a bomb going off if it trips. And why it takes a hydraulic pump to reset. Side note: The Pacific DC Intertie was the largest in the world until the 3 Gorges Dam interties--and it dated to the Kennedy administration and used vacuum tubes. https://en.wikipedia.org/wiki/Pacific_DC_Intertie https://en.wikipedia.org/wiki/Pacific_DC_Intertie

jerkstate 9y ago
Cool, thanks for the additional info. TIL!