Transformer cans with no primary

I saw something interesting in Philadelphia a couple of times. A
large transformer can on a pole to feed nearby homes/businesses. Directly
below it on the same pole was a second transformer can, quite small.
It had leads leading into the same tangle as the large transformer's
secondary leads, but _no_ primary distribution connections. I also saw
one of these small cans on a pole with no primary HV on it at all. Wonder
what they are for. I can only guess transforming one low voltage to
another low voltage.
(Saw some other 'creative' wiring. Such as a single phase primary for a
side street from a main street attached to one of the 3 phases with an
insulator. Not to a pole or crossarm, to the wire itself. The insulator
was jumpered to the main wire, making it quite unnecessary.)
Reply to
Michael Moroney
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in article caj2vd$35r$ snipped-for-privacy@pcls4.std.com, Michael Moroney at snipped-for-privacy@world.std.spaamtrap.com wrote on 6/13/04 7:36 PM:
It is hard to know from your description just what you see. My guess is that your "can" is not a transformer. It could be a capacitor--but who knows?
Bill
Reply to
Repeating Rifle
[snip]
insulator
Perhaps not a jumper but a fuse link???
Drew
Reply to
D.F.S.
Didn't get a real close look, but it looked like just a piece of wire to me.
Reply to
Michael Moroney
It looked like any other transformer can. It had several lugs for heavy wiring on the side of the can just below the top, like most other transformers. Wiring went from them to the bundle at mid-pole which leads to buildings, same place as the secondary wiring from the large transformer. The only difference was no HV bushings on the top of the small cans, and no HV wiring to it. And they are quite small.
I have no idea what is inside. I have never seen capacitors wired to secondary wiring on the poles.
Reply to
Michael Moroney
I have a guess.
You usually see these below capacitor banks and not transformers, but there are small cans that contain an inductor (just a coil of wire). The purpose of this is to block the "load control signal" (high frequency) from draining to ground. Load control signal switches the downstream load control relays on and off during times of high load. Some businesses and homes sign up for this service to cut power to optional power devices (water heaters, etc) and they get a discount rate.
My only guess why it is on a pole only with transformers is that the customer may have some capacitors on the supply side. ???
The inductors do look like tiny transformer cans.
Reply to
Dave P.
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.
Reply to
Michael Moroney
| 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.
Reply to
phil-news-nospam
Photo is at:
formatting link
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.
Reply to
Michael Moroney
THe link does not work for me.
Charles Perry P.E.
Reply to
Charles Perry
Odd. Now it works. However, I can't tell anything from the picture. It would take pictures from other angles to even have a chance of identifying what is going on.
Charles Perry P.E.
Reply to
Charles Perry
| snipped-for-privacy@ipal.net writes: | |>| |>| 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:
formatting link
| | 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.
Reply to
phil-news-nospam
The top can does have 3 primary connections and 4 secondary ones so I am pretty certain it is 3 phase. The service feed that goes off to the top does go to a small shop and the meter did read 120/240V single phase. The one off to the left goes to the next pole and I didn't look to see what it feeds. Both are definitely fed off the leftmost terminals of the small transformer. One wire from the large transformer goes only to the small one. Again, I didn't look to see what the other two hots of the large transformer feeds, whatever it is it apparently only uses two of the three phases.
I won't be in that area again until November and I will try to get more info/better shots then.
Reply to
Michael Moroney
I see the street lamp on the same pole.
Maybe it is some kind of constant current regulator for the street lamps (the seriies system used to be quite popular back when transformers were far apart because all the lights had about the same brightness.)
Just a thought.
Reply to
John Gilmer
| snipped-for-privacy@ipal.net writes: | |>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. | | The top can does have 3 primary connections and 4 secondary ones so I am | pretty certain it is 3 phase. The service feed that goes off to the top | does go to a small shop and the meter did read 120/240V single phase. | The one off to the left goes to the next pole and I didn't look to see | what it feeds. Both are definitely fed off the leftmost terminals of | the small transformer. One wire from the large transformer goes only | to the small one. Again, I didn't look to see what the other two hots | of the large transformer feeds, whatever it is it apparently only uses | two of the three phases.
Looks to me like a total of 4 wires going down the pole, so that is more than just two phases out of three. Two of the wires definitely go straight up to the top transformer. The others are just not clear.
Here's a PDF that has a couple pictures of pole-mount 3-phase transformers. The first one on the first page (the tall one in the group) looks like the one in your picture.
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I've never seen a pole-mount transformers with no primary bushings, so this would definitely have piqued my interest, too, if I had encountered it.
Reply to
phil-news-nospam
Any chance the small can is for power factor correction, capacitors connected to the low voltage side? That didn't seem reasonable from some of the things that were shared. But, ... --Phil
Reply to
Phil Munro
It's a "lighter Pot". It's powering the street lighing. Not the usual configuration. The service and the street lighting are not at the same voltage. It looks like the transformation was done at lower voltage.
Reply to
BJ Conner
Sorry, a NAT router has been acting up lately.
In the unlikely event a larger image (390K) of the same photo helps trace things, it is at:
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I should have taken another picture or two but my wife thinks I am odd enough as it is. :-)
It really looks like it is powering the small store to me. (aside: I remember the odd configuration that powered street lights in Buffalo, which had incandescent lights all in series. One bulb went, they all went. Maybe 10-20 on each string.
There were three things on the pole that powered them, a large transformer can, a smaller can and something else I couldn't identify)
Reply to
Michael Moroney
|>It's a "lighter Pot". It's powering the street lighing. Not the |>usual configuration. The service and the street lighting are not at |>the same voltage. It looks like the transformation was done at lower |>voltage. | | It really looks like it is powering the small store to me. | (aside: I remember the odd configuration that powered street lights in | Buffalo, which had incandescent lights all in series. One bulb went, they | all went. Maybe 10-20 on each string. | | There were three things on the pole that powered them, a large | transformer can, a smaller can and something else I couldn't identify)
One of them was a current regulator to keep the current constant regardless of how many lights (within a range) are in series.
Reply to
phil-news-nospam
If the upper can serves 480Y/277V 4w, the lower may be something like 480-120/240V 1ø.
Else, the small can may be housing a "revenue check" meter.
?s falke
Reply to
s falke

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