Comments by "SeanBZA" (@SeanBZA) on "Sabine Hossenfelder"
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DC does not allow smaller cables, it just means you can use the cable at the rated voltage, and do not need to make allowance for the crest factor of the cable. While this is useful on HVDC (150kV or higher) power lines, where you get 40% more power transmitted, for the same current, and the same peak voltage, it makes absolutely no difference for lower voltages, or for anything that is going to be common in industry or homes, where your standard house wire in use has a 1kV rating.
But it is never run even close to this, the only place where you run regular cable at higher voltage is in tunnels, where the supply for lighting and fans is typically 700VAC, as that is a big increase in power transmitted down the tunnel, for the same diameter cable, over using the standard 400VAC 3 phase supplies they normally use. Allows use of standard industrial cables and fittings, rated for 1kV, and also means they can put nearly double the load into the tunnel for lighting and fans, as they now just use either local autotransformers, to provide the local run, or have motors wound for 700VAC operation instead. Saves a lot of money if you do not need to make the tunnel 1m wider, to get the high voltage cables in and still provide the required separation, and also the need to dig big equipment rooms to house the big transformers, as opposed to simply running the cables on the walls, or under the road bed, where they are well protected, plus your control gear is almost all mostly off the shelf of Schneider or ABB, and not too much that needs custom manufacture and certification, as the regular switchgear is already rated in the most part for 1kV use under the Low Voltage directive, Low Voltage here referring to power distribution under 1000V.
DC is common, just that it is typical in Telecoms, where you get a lot of equipment that runs off a nominal -48VDC rail, based on old telephony battery bus voltages, and it is also common in large industrial equipment with a lot of inverter drives, where they use a DC bus to connect all the inverter units, so that energy recovered from the one unit as it slows down a motor can be used by others to power them, instead of being dumped as heat in a brake unit. there you find 400VDC, 600VDC as common bus voltages.
However a big issue is fault protection, as DC rated breakers, fuses and disconnects are quite a lot more expensive and larger over the same rating AC units, as the AC units have no need to break an arc, as it is naturally going to be extinguished twice per cycle, so all the unit has to do is prevent it from striking again, unlike DC units, which actually have to cool it down till it goes and stops, by no longer being able to ionise air. DC you can pull a very large arc, while AC it tends to go out easily. Look up the people doing welding using only solar panels in the sun, nothing else, and that they can draw pretty big arcs out of them, along with solar panel fires that only stop when the sun goes down, or the panels burn out completely.
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@steveboverie9432 Who does the injection also is the thing, I learnt from a hard as nails registered nurse just how to administer injections, because she would swab the area, then get ready with the needle, and tap the area a few times with the swab, to get your skin and nerves used to sudden taps, and then slip the needle in instead. You would not notice it. She almost always was the one doing the pediatric work as well, because she would not cause any sudden pain to the infants and children, so they would not cry, and thus not stress the rest of the children in the line out either. Plus she always had a big bottle of sweets, that she gave to them afterwards, as reward. But i did see her inflict needed pain on some, giving them a teaching reminder.
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Yes, I do not mind my dentist, he has a great chairside manner, and he works to minimise pain at all steps. Simplest thing he does is put a small amount of the injectable lidocaine onto the gum first at the site, and wait a minute, looking at the rest of your mouth at the same time, then going in, putting a small amount in the now numb area, and then another minute of waiting, then finally the full dose. You feel nothing at all, which helps as I am insensitive to the local, so the regular dose normally means I do feel pain, but it is manageable for the duration.
Fun thing about the 'caines is that they sublimate, or at least that is what they say in the police evidence room, when the amount they show on trial is half the amount registered at the bust.
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