On Sat, 12 Jun 2004 01:12:56 +0000 (UTC) Michael Moroney wrote: | snipped-for-privacy@ipal.net writes: | |>On Fri, 11 Jun 2004 19:54:09 +0000 (UTC) Michael Moroney wrote: |>| snipped-for-privacy@ipal.net writes: |>| |>| Having the maximum voltage being 139V vs 208V doesn't seem to be much |>| of an advantage. Presumably all the 240V motors are all insulated |>| sufficiently for 240V (or at least 208V). Also load imbalance for |>| lighting off a center tapped phase shouldn't be an issue if the power |>| co. knows of it and installs proper transformers. I've seen a few |>| installations which appear to be 240V open delta with a large transformer |>| with a grounded center tap and a small one for the B phase. (Including |>| several in a residential neighborhood in Baton Rouge LA. Whole house |>| air conditioners using 3 phase?) | |>If going from 139V to 208V (line to ground) is "not much", then going up |>to 277V (line to ground) would be "not much more". So why not run 480Y/277 |>everywhere that three phase is needed. Europeans already use 400Y/231 which |>is in between these. | | That's different. Going from 240 delta to 240Y/139 doesn't change the | voltage the device sees, while 480Y/277 certainly does! The only real | differences are line-to-ground voltages.
But in terms of safety, 480Y/277 is 277 to ground, while 240D-CT is 208 to ground on one phase. The ratio between them is 1.333333 while the ratio between 208 and 139 is 1.5 (using the exact derived values).
|>Sure, proper transformers can allow more lighting power. But then it's not |>a simple delta anymore. But the power company doesn't like this extra cost |>even if it's a small teaser for the B phase. | | Are 139V transformers an off-the-shelf item?
I have seen them in the form of dual winding 277x139. As to whether they are off-the-shelf, I cannot say. If utilities wanted to do 240Y/139 more, they certainly would become so. And it might not be that hard to make a dual-tapped dual-winding (120-139)x(240-277) transformer that could do a wide range of configurations in a single stock (per kVA rating) model.
| (Also if an idiot electrician causes problems if he wires something to | the stinger phase in a 240V delta, consider the same idiot wiring outlets | to a 139Y/240 board. Everything would probably work OK...except | incandescent bulbs would burn out really quickly...and occasionally some | random device will burst into flames...)
There would have to be separate panel boards for 240Y/139 and 208Y/120. If properly marked, I think the error rates would be no worse and might even be less with 240Y/139. An electrician would have to be blind to make a mistake with 240Y/139. But with 240D-CT, he'd have to only be color blind to make a mistake.
They do have a similar issue in Japan. 100 volts is the nominal there. But three phase is 200Y/115. I'm sure they are not mixing things up.