On Wed, 30 Jun 2004 02:30:34 +0000 (UTC) Michael Moroney wrote: | snipped-for-privacy@ipal.net writes: | |>On Tue, 29 Jun 2004 19:57:48 +0000 (UTC) Michael Moroney wrote: | |>| Was back in Philly this weekend and got a better look at some. |>| The ones I looked at had 4 lugs on the side of the can just below the top. |>| Some had apparent kVA ratings marked on the can like regular transformers, |>| such as 7.5, 15, 25. One had "240V" stenciled on it. One had 2 lugs |>| marked X1 X2 (couldn't make out the others) Another had one lug marked N. |>| Many sat below "3 phases in a can" transformers which seem to be common |>| there. | |>Could you tell where the power went to? | |>Could be just about anything. One possibility is a boost autotransformer. | | Photo is at:
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| | This was one of the few ones where the wiring is somewhat traceable and | not bunched together so the individual wires are not visible. | One phase of the 3 phase main transformer seems to only go to the | small can (lug on the right). Two wires come from lugs on the left seem | to go to the service for a small store and to the next pole (off to the | left). It appeared to have single phase service. From this, my guess is | a 277V to 240VCT (or maybe a 120 or 208 to 240V) transformer. Probably an | autotransformer. I should have looked more carefully to see where the | other phases of the large transformer went.
As Charles Perry suggested, pictures from other angles would help. If you do take some more, take them in pairs about 1 foot apart within each pair. That way I can set them up for 3-D stereo viewing.
It does look like the upper transformer is 4-wire 3-phase. I see 2 primary fuses, and presumably the third is hidden, so it is either 3-phase, or just a single phase with line-to-line primary. But I'll say 3-phase because it looks like the drop down the side of the pole is 4-wire. The lower one might be to derive a normal single phase voltage (e.g. 120/240 instead of 120/208) for the other two service drops (one to the left, and one going to the top of the picture frame). I would say they are using a 120/240 transformer (without primary bushing) fed with 120 and deriving normal 120/240 as an autotransformer for this trick.