Thanks to bjarney for the photo and following notes:

An interesting picture, and certainly like nothing you'd see in my part of the world.

I can make out the secondary links between the transformers and connecting to the 240V lines in delta configuration.

Why did the PoCo install two services run with separate 240 delta and 120/240 3-w feeders, rather than just running 4 lines to each building and then tapping off as needed for each meter?

The only reason I can think of is that with the 240 delta likely to be used for motor loads, using separate feeders could minimize the dimming of lights during the starting surges.

What's the significance of the yellow marker bands on the poles?

Paul
Around here the yellow bands just say High Voltage. In this case it looks like if someone got high enough they would already be in a world of trouble!

Bjarney,
Thanks for submitting that picture, mate!.
You're quite right, the Primary Delta system can be easily seen there.
Just a small point, regarding what Nick mentioned about people climbing poles, this arrangment above, by virtue of how the wires on the bottom set of cross-arms, more or less provides it's own barrier to persons wanting to get a better look at the country-side.
BTW, are those transformers bonded together and Grounded?.

Paul, I don't know the history of two sets of three conductors, even though indeed derived from a ‘4-wire’ source. The only clue I have is that local utility estimators would gripe about requests for wye-secondary transformer banks, for they could not serve any of the routine 'Edison three-wire' services from it. [Old habits die hard, I suppose.]

The yellow bands are most likely “Hi Signs” [lineman slang for ‘HIGH VOLTAGE’ signs] like the third item on www.techproducts.com/pg19.htm Their use probably evolved from a landmark legal case where some crazed idiot climbed a pole and got toasted.

Trumpy, I think the case-grounding practice has probably evolved along with secondary grounding—that is, used to be floating but now is rarely the case.

Bjarney,
How are the connections made between the lines and the tails that feed the Xformers?
Are those Line-Tap nuts?, used over in the US?.

They're probably silicon-bronze split bolts—"bugs". With all the aluminum used nowadays, a mechanically-bolted "PG" [parallel-grooved] connector or hydraulically compressed "H-tap" is the norm.

I wondered if those yellow bands did just say HIGH VOLTAGE, but as Nick has said, it looks as though by the time anyone was high enough to see them properly he would already be surrounded by the primary lines linking down to the transformers.

Wonder what happened to that short cross board at the left-hand side? I have a vision of a utility worker needing a small piece of board for some reason and sawing it off the end!

More confirmation I suppose of just how firmly America adopted delta configurations for secondaries in earlier times.


[This message has been edited by pauluk (edited 02-15-2004).]

Good pic, Bjarney!

I believe the 2 sets of 3 wire feeders were installed so that the utility could meter the lighting and power loads separately.
Then they could charge different rates for each.

This setup was commonly used around here(Vancouver, BC, Canada). One business I worked at several years ago still has this in place. I can also tell you that about 90% of additions over the years have been added to the lighting service

I can speculate on the popularity of delta voltages in US distribution, but only with personal, anecdotal correlation. Probably some tendency towards delta secondaries in utility distribution grew with the practices of system grounding and related codes that grew more common, which was a passionate issue in the early 20th century. A breakpoint of sorts in AC electrical-history accounts seems to be 150 volts. The ‘habit’ seems to be, if low-voltage service entrance could be grounded to keep conductors under 150 volts to ground—it was, where if greater than 150 volts, grounding was optional with various arguments for the acceptability of the two practices.

Another small difference has been the tendency for 2:1 voltage ratios {for transformers and motors} in the US, corresponding to dual/split/tapped windings, versus 1.732:1 ratios popular in other areas, corresponding to phase-to-phase and phase-to-neutral voltage inherent in wye windings.

Habits are hard to break, but a classic power-systems text [Beeman’s Industrial Power Systems Handbook] has advocated the use of 208Y/120- and 480Y/277-volt systems since 1955.

Here is an illustration of plain-vanilla 1ø distribution-transformer terminal markings used in the US. It is rountine that only three secondary terminals/connections are brought out of the case, where internally they can be rejumpered for series/split or parallel operation.

There's a bunch of these types of setups around here (the 1Ø Pots on a "Shelf" setups).

I'll get some pics tomorrow, then post to this thread.

Scott35

Here are some pics of "H Shelf" Transformer setups in my area.

These are in Anaheim, CA. (City of Anaheim Department of Water & Power).
Have not seen any of these in SCE's territory surrounding us, but have seen many
in the City of Los Angeles (LADWP).

As you will see, each setup is different from the next.



Image 1: 3Ø 4 Wire Wye setup.

This one is in back of a Masonry Building that's been around my area since
late 1950's. I remember this setup being there since I was at least 3 years old.
Originally, it fed the building as a single Tenant. Around 1980, the shell
was partitioned for three Tenant spaces, so new S.E. risers were added.
The original part is still fed via feeder duct.



Image 2: Two Separate 1Ø 3 Wire Transformers.

This setup was, at one time, a closed Delta 4 Wire system. Currently there are two
separate 1Ø Transformers of apx. 75 KVA size. Each Transformer feeds a single
400 Amp Service Section.
Back in 1970's, this was a closed Delta setup - with an additional 1Ø Transformer
located on an adjacent pole. Now the 3Ø system is a 4 wire Wye of apx. 45 KVA size,
located on the pole, which used to have the 1Ø Transformer on it.



Image 3: Three Separate 1Ø 3 Wire Transformers.

This setup has three individual 1Ø 3 Wire Transformers - not connected at the Secondaries
to form a Polyphase system. Each Transformer feeds a 400 Amp section.
Have been in this building many times (it's one of the banks we worked for).
The building has 3Ø service derived from a closed Delta 3 Wire arrangement on an adjacent
pole. This pole is within 15' of the shelf.
BTW, Electure may recognize this location, along with the location shown in Image 5.



Image 4: Overall View Of The Location Shown In Image 3.

This is the same bank location.
Electure's gotta recognize this one!




Image 5: 3Ø 4 Wire Closed Delta Arrangement.

Sorry for the poor image quality! The Sun really makes the digital camera sad...
If you can make out the arrangements here, the center Transformer is huge!
It's one of those with the cooling tubes on the sides. Might be 167 KVA with
two 75 KVA Xformers on the sides.

I'll see about getting a better shot of this setup.

That's all for now!

Scott35

Thanks for all the extra photos Scott.

You just won't see constructions like this over here. About the largest xfmr set-up you're likely to see on poles is something like this:


This is a standard 3-ph xfmr arrangement with 11kV delta primary and 240/415V wye secondary, rated 100kVA.


[This message has been edited by pauluk (edited 02-18-2004).]

Scott — Your image 5 is interesting with the set of “staggered” transformers. As an example of how ingrained 240/120V delta and open-delta service can be, here are some [MSWord] pages from {El Paso Electric} utility’s distribution standards. There are some charts for determining acceptable “combination” 1ø and 3ø loads for various-sized sets of transformers. See Delta Loading

[Small aside — I’d hate to have to pull the fuses on the righthand set of cutouts. I guess you are supposed to stand on the platform to do it.]

Scott, I don't know where that is! (Probably my backyard, ehh?)

Paul, isn't that transformer mounted very low to the ground?

Bjarney, maybe it's my computer, but that link froze me up

[This message has been edited by electure (edited 02-18-2004).]

I was able to open the link, but it was kinda slow going. I'm on a dialup connection this week.

Bill

Oops, sorry Bill.

Delta Loading {~300KB} is six pages excerpted from an oringinal file {~5MB} at http://www.epelectric.com/internetsite/ybusiness.nsf/By+Subject/Distribution+Standards+Overhead/$file/dso+section+TD.pdf

It's actually higher than the photo makes it appear. The grass and bushes around the base of the poles are quite tall, and the adjacent roadway is elevated several feet above grade at that point as it's the lead-up to a small bridge over the river.

I drive over that stretch of highway quite often, and from the car the transformer always seems to be low.

Scott35's transformer pictures spark the memory of one version of utility-supplied three-wire delta service I found at a pretzel plant in El Segundo, CA {north of Disneyland ~15 miles.} The building had an original 800A 240V 3ø 3-wire corner-grounded-delta service, with several drytype 1ø transformers for 120/240V 1ø 3-wire feeding lighting and 120V convenience outlets. More recently, a 400A 120/240V 1ø 3-wire service had been added. The plant’s maintenance crew did onsite electrical troubleshooting, and some were very confused by the two different grounded-circuit conductors {all correctly white} that had completely different voltage relationships. In many places in the plant, they found circuits with 240V to ground, and in other places 120V to ground, but with no distinct phase/color-coding or markings to readily differentiate the different systems.

At the end of two weeks of training to understand their electrical system and work on it safely, out of a crew of about 8, a couple of guys understood it and were committed to teach others what to expect, and why the plant has more that one set “neutral” conductors. In corner-grounded-delta circuits the “white wires”/grounded-circuit conductors were not neutrals by Code definition, but “white wires”/grounded-circuit conductors in 120/240V circuits are. To complicate matters even more, the corner-grounded 3ø system used some 2-pole fusible switches, and both two- AND three-pole circuit breakers.

[The plant’s 1ø and 3ø transformers were served by once regionally popular 4800V 3ø ungrounded-delta distribution.]




[This message has been edited by Bjarney (edited 02-21-2004).]

Scott 35
I stumbled (usual mode of travel) across that xfrmr bank, and it's next to the Bank, and right around the corner from my house.
Oh, great! Now I'll get this endless addiction to taking pictures of powerlines and transformers.
(You know, my whole street is going overhead to underground right now. Time to shoot pics).

May be time to start "Electricians Anonymous?"
...S


[This message has been edited by electure (edited 02-24-2004).]

Paul;


You're welcome! Glad to be part of the discussion.


I have seen a bunch of Polyphase Transformers for pole mount around these parts, similar to the one you have posted. Only the enclosures are a bit different in appearance, plus the H.V. Bushings normally are mounted on the top and the L.V. Bushings are on the front.

Bjarney;


Ya, the center one is huge, as compared to the outer two Transformers. It also has the cooling tubes, whereas the others do not have these.


Thanks for the linked items! Added them to my ever-increasing Library 'O Info.


Electure;


DING!!! Give the Man a Cigar!
I have been in this building a few times. Last time was to install a Card Reader Entry system at the side door, and also do an ATM upgrade (survey, design, install).


You're Wife is really going to be puzzled now!
My Wife still laughs about it - like the times we pull over suddenly and out comes the Digi Camera - aimed at Power Lines / Equipment!
She used to joke about this stuff + the "stalking trains" stuff, but it happens so often it lost all humor to her!


I was wondering what was going on in your area! Wonder if our area is on the list too?
Street renovation is taking place currently. City workers have been patching like mad (smell of tar everywhere). Resurfacing is set for June.



In the words of "Duff Man"...
"Ohhh, Yaaahhhhh!!!"

Scott35