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Joined: Apr 2002
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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.

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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.

[Linked Image from 6l6.net]

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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


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
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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.

[Linked Image]

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.

[Linked Image]

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.

[Linked Image]

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.

[Linked Image]

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

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


[Linked Image]

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


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
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pauluk Offline OP
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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:
[Linked Image]

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).]

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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.]

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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).]

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

Bill


Bill
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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

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pauluk Offline OP
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Quote
Paul, isn't that transformer mounted very low to the ground?

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.

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