| Thanks to all for a good discussion. The spa building is still in the | planning stages (without existing service) so that will figure into | the specifications. Much useful input was given from these | discussions.
That will mean you have a choice in the way you do this. You could go with getting 208Y/120 service and smaller transformers to take 208 volts up to 240/120CT. Or you could go with that or other three phase voltage and use transformers for your full capacity. With that choice you can either go with 240/120CT for the whole building, or do 208Y/120 and more transformers to get 240/120CT just for the tubs. You will need to see what else you might have that needs, or works better, on 240/120, and evaluate the cost of all your options.
| The inventors of the transformer (Lucien Gaulard & John Gibbs) | experienced years of difficulty with their invention because they kept | on hooking up their circuits with the primaries in series instead of | parallel. The end result was that they could transmit power for long | distances, but the practicality of the invention suffered due to poor | load regulation. The parallel primary connection (for multiple | transformers) that seems so obvious to us today, was not perfected | until a theoretical understanding was applied by men like Tesla, | Stanley, and Westinghouse.
You mean multiple transformers feeding different loads where the primaries for each are in series? Yeah, that would be bad.
You can get transformers would double primaries which can be wired either in series or parallel. One rated 480x240 would handle 480 volts when wired in series and 240 volts when wired in parallel, with the same kVA capacity.
If you get 480Y/277 power, you could get one 3 phase transformer to take 480 volts in to a delta winding, with a secondary of 208Y/120 (three 120 volt windings in wye configuration). Then instead of doing
208 volts to 240/120CT, you could tap off the 480 volt side with the tub transformers and use the cheaper (because they are more common)
480x240 to 240/120 transformers that are out there.
| Lucien Gaulard was born in Paris in 1850. Gaulard was a French | scientist, primarily interested in chemistry of explosives, but later | he shifted his interests to electrotechnics. He developed a | thermochemic battery and he is particularly known for his work with | induction coils (transformers). In 1882, Goulard and his English | colleague Gibbs patented a system of distributing power using | alternating current and two-coil induction devices. They used devices | (then known as secondary generators) of the Ruhmkorff type in the | first alternating current distribution system and had a 1:1 ratio and | were used with their primaries in series.
Ah, I see. They probably didn't have a real grasp on the designing for particular voltages, capacities, saturation, heat rise, etc, as we (not me personally, but those who do make them) do today.
| Gaulard's transformers were successfully presented in 1884 on the | international exhibition in Turin. The farthest lamp fed, on the | Torino-Lanzo railway line, was at 40 km distance from the 2,000 V | generator with 133 Hz frequency. The series connection led to | unsatisfactory regulation unless all the transformers were equally | loaded. However, these transformers were in use until 1912.
Interesting frequency. I wonder how they picked that one.
| Gaulard was ingenious, but unlucky inventor. During his life his work | was not recognized in France. Gaulard fell in depression state and | seems he went mad, was sheltered in clinic where 1888 died the 26 | November. Now Gaulard fame is memorized with tombstone in the railway | station of Lanzo, there is also a street with his name in Paris. | | This man was the co-inventor of one of the world's most revolutionary | inventions that gave the world the ability to transmit electric power | for long distances, but for some reason he just couldn't get the | connections correct.
Perhaps he was victim to the same kind of misunderstanding I once had where transformers didn't make sense (despite knowing they should). It seemed to me back then that having _more_ windings in the primary would create _more_ flux, and that should produce more "secondary generated" power. Of course the reality is more winding is more impedance and less current. You don't want to tie them all in series with each other on different loads, or else you are making current transformers out of them (and pathetic ones at that).