XPost: rec.arts.comics.strips   
   From: tl@none.invalid   
      
   Scott Dorsey  wrote:   
   >Thomas Koenig   wrote:   
   >>But I read upthread about 220 V (or 240 V) in the US being supplied   
   >>by having two opposite phases.  How is that generated from three   
   >>phases?  Sound weird.   
   >   
   >Center-tapped transformer.  You have your 24KV mains in three-phase   
   >but you take one phase put it into a 24KV:240VCT with the center tap   
   >as your neutral and now you have two opposing hot legs off of one phase.   
   >(This is why it's called single phase power and not two-phase power,   
   >because both legs come off the same phase of the distribution network.)   
      
   It should also be mentioned that US/Canada *also* uses the 208V/120V   
   3-phase, that's where the 208V comes from (it's what you get between   
   two phases in a 120V 3-phase system).   
      
   It's rarely used for normal houses (but someone mentioned it was an   
   option) but it's very common (universal?) in larger buildings - which   
   is why most medium-sized NA equipment accepts both 240V (domestic   
   split-phase) and 208V (between two hots on a 120/208V 3-phase power).   
      
   If it's a LARGE building it may well have an onsite transformer taking   
   it down from grid voltage (14kV?) to a building distribution 3-phase   
   voltage (AFAIK often 480/277 in the US, 600/346V in Canada) with   
   distributed transformers taking it down for final delivery to either   
   120+120V split-phase or 208/120V 3-phase. Seen this done in several   
   buildings.   
      
   Then there's datacenters, this was a decade plus but every US   
   datacenter (20+) I visited back then used 208/120V 3-phase as final   
   delivery because it's cheaper to provide (needs less Cu or Al for a   
   given load) and allowing them to provide all three types of power   
   their end-users want (120V, 208V or 208/120V 3-phase circuits are all   
   common).   
      
   Today with AI racks at 100+kV each (soon 350+) and the equipment   
   mostly wanting 48V DC I expect these racks gets fed higher voltages   
   and likely 3-phase, the amperage gets ludicrous if you don't.   
      
   I don't have details on this but I expect they started with 480/277 or   
   600/356V (see above) due to availability of equipment but I DO know   
   there's also people planning for 800V+ to racks.   
      
   That voltage choice comes from components for EV DC fast chargers now   
   being easily available and cheap - EV DC chargers are 400V (older) or   
   400V/800V (newer) "nominal" chargers, these must provide up to   
   something like 500V or 1000V (DC) peak final charging voltage   
   respectively (peak voltage of battery packs are much higher than the   
   nominal voltage for most but not all chemistries used in cars).   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)