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Joined 1 year ago
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Cake day: June 14th, 2023

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  • I’m not sure there are any power grids past the tens-of-megawatt range that aren’t just a 2/3/4 terminal HVDC link.

    Railway DC supplies usually just have fat rectifiers and transformers from the AC mains to supply fault current/clearing and stability.

    Ships are where I would expect to start seeing them arrive, or aircraft.

    Almost all land-based standalone DC networks (again, not few-terminal HVDC links) are heavily battery backed and run at battery voltage - that’s not practical once you leave one property.

    I’m sure there are some pretty detailed reports and simulations, though. A reduction in cost of multi-kV converters and DC circuit breakers is essential.




  • PV inverters often have around 1-2% losses. This is not very significant. You also need to convert the voltage anyway because PV output voltage varies with light level.

    Buck/boost converters work by converting the DC current to (messy) AC, then back to DC. If you want an isolating converter (necessary for most applications for safety reasons) that converter needs to handle the full power. If it’s non isolating, then it’s proportional to the voltage step.

    Frequency provides a somewhat convenient method for all parties to know whether the grid is over- or under- supplied on a sub-second basis. Operating solely on voltage is more prone to oscillation and requires compensation for voltage drop, plus the information is typically lost at buck/boost sites. A DC grid would likely require much more robust and faster real-time comms.

    The AC grid relies on significant (>10x overcurrent) short-term (<5s) overload capability. Inrush and motor starting requires small/short overloads (though still significant). Faults are detected and cleared primarily through the excess current drawn. Fuses/breakers in series will all see the same current from the same fault, but we want only the device closest to the fault to operate to minimise disruption. That’s achieved (called discrimination, coordination, or selectivity) by having each device take progressively more time to trip on a fault of a given size, and progressively higher fault current so that the devices upstream still rapidly detect a fault.

    RCDs/GFCIs don’t coordinate well because there isn’t enough room between the smallest fault required to be detected and the maximum disconnection time to fit increasingly less sensitive devices.

    Generators are perfectly able to provide this extra fault current through short term temperature rise and inertia. Inverters cannot provide 5-fold overcurrent without being significantly oversized. We even install synchronous condensers (a generator without any actual energy source) in areas far from actual generators to provide local inertia.

    AC arcs inherently self-extinguish in most cases. DC arcs do not.

    This means that breakers and expulsion type fuses have to be significantly, significantly larger and more expensive. It also means more protection is needed against arcs caused by poor connection, cable clashes, and insulation damage.

    Solid state breakers alleviate this somewhat, but it’s going to take 20+ years to improve cost, size, and power loss to acceptable levels.

    I expect that any ‘next generation’ system is likely to demand a step increase in safety, not merely matching the existing performance. I suspect that’s going to require a 100% coverage fibre comms network parallel to the power conductors, and in accessible areas possibly fully screened cable and isolated supply.

    EVs and PV arrays get away with DC networks because they’re willing to shut down the whole system in the event of a fault. You don’t want a whole neighborhood to go dark because your neighbour’s cat gnawed on a laptop charger.






  • It was a few years back, but after it hit ChromeOS EOL I’m pretty sure it just got some KDE distro; I don’t think I even used LXDE. Didn’t need to do much.

    I was mostly using it for web browsing, forums, spreadsheets, documentation etc. Nothing particularly strenuous.

    I did have one really fun time of modifying PDF engineering drawings by opening them in Libre Office Draw which it handled kinda OK.

    It did get a 240GB SSD but everything else was soldered.








  • HDMI and DP do not carry their signals in the same way. HDMI/DVI use a pixel clock and one wire pair per colour, whereas DP is packet-based.

    “DisplayPort++” is the branding for a DP port that can pretend to be an HDMI or DVI port, so an adapter or cable can convert between the two just by rearranging the pins.

    To go from pure DisplayPort to HDMI, or to go from an HDMI source to a DP monitor, you need an ‘active’ adapter, which decodes and re-encodes the signal. These are bigger and sometimes require external power.



  • While braking suddenly is something that can happen on the roads, it’s still a potentially dangerous maneuver. It’s often better than the alternative (crashing into something/someone), but there’s still risk involved.

    If these vehicles are doing panic stops frequently and unnecessarily, that’s a major problem. It’s a common type of insurance fraud, for starters.

    I wouldn’t be surprised to find that the computer has a faster initial braking response whereas it takes time for peoples’ feet to fully depress the brake pedal. A shorter time from the brake lights coming on to the brakes being at full service pressure.