Unusual electrical service wiring

I was looking at a webpage that showed typical power transformer connections for different types of services. In addition to
the usual 120V/240V single phase and 120V/208V three phase configurations, they showed a few odd ones One was 3 240V transformers in a delta configuration with the center tap of one of them grounded. The leg not connected to the grounded transformer was referred to as the 'wild' leg and apparently carries a voltage of 208V to ground. What sort of devices would one have that would cause one to request such a service from the electric company? 3 phase motors with a requirement for 240V delta seem like they'd be kind of oddball, esp with 208V equipment being common. A motor connected in a Y would be even odder, it would get 138V (if my math is correct) and its neutral would be 70 volts above ground.
Also in the examples shown sometimes one of the 3 transformers (not the one with the ground) was omitted.
Even weirder was a "Scott" arrangement, two transformers fed from 3 phases so to produce two phases at 90 degrees. What would want to be fed with _that_?
I've also wondered about a small industrial building. It has 3 individual heavy wires from the pole to the building, the pole has 3 "cans". I found this odd, there should be 4 wires. Looking closer the secondaries are in a delta configuration and none are grounded as far as I could see. The same building has a second feed which appears to be a standard Y setup, 3 hots and a neutral. So the first must be some special equipment.
Also what are the advantages of Y and delta configurations for power wiring? Y provides a natural neutral for one. For secondary wiring (the 11,000 volts or whatever that run down your street) it appears most of it is Y connected but older is delta. Why? From what I can see the very high voltage power lines are always delta. Why? Also, if a power line is described as carrying 345kV, is that phase to phase or 345kV phase to ground?
--
-Mike

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That is a 240V power bank. It provides a three phase 240V delta service as well as 120V from the center tapped transformer for "lighting". That transformer is usually larger than the other two and is used to serve all single phase load in the facility. Nothing odd about it. It is a quite common service for commercial facilities.

Open delta. Provides three phase service with only two transformers. Works well when the three phase load is well balanced and there is little, or no, single phase load. Again, not unusual at all.

Scott T was developed to supply three phase loads from a two phase distribution system. This still happens from time to time. It is rather rare. I know of a few radio/television broadcasting locations with this type of service since it was cheaper than running all three phases the multiple miles to the top of the mountain.

Delta service is not for "special equipment". Motor drives run on three phases, no need for a neutral in most cases.

You sure have a lot of questions. The comparison of the advantages/disadvantages of delta vs wye could keep this group hopping for months. One advantage of delta is a savings in the amount of wire that must be run.
The "11,000 volts that runs down your street" is not secondary, it is primary and is referred to as medium voltage. It is not 11kV, but usually 12.47, 13.2, 13.8, 25, or 34.5kV. Some 4kV also exists. Most of the US uses a 4 wire multigrounded wye setup. There are many reasons; two of which are that most load is single phase and the other being that it is easier to detect single line to ground faults (these are the most common faults).
345kV refers to the line to line voltage.
Charles Perry P.E.
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<snip>

must
You certainly *do* have a lot of questions.. :-)

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It depends which country you are talking about (silly Americans think they run the whole world! ;-) :-)
Down under, the most common sight around the back blocks certainly is 11kV Delta (no neutral or ground). As you get further out of town you find 22kV, 33kV, 66kV and finally 132kV. The easiest way to check the voltage in use is to count the number of disks on the insulators.
Pole-mounted transformers (D/Y) convert the high-voltage primary to low-voltage (415V) secondary with a neutral and an earth at each pole. The main reason for doing this is to save on cable costs.
Oh, and in the country you might find a 22kV SWER line, but that's another story.
Cameron:-)

Or phase to phase if you prefer ;-)

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<snip>

usually
Well, I did say that I was talking about the US and he did say there was 4 wires, which means he is not in Australia.
<snip>

SWER is some odd stuff, but it does work.
Charles Perry P.E.
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US
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I know you did... but you also said "It is not 11kV, but usually 12.47, 13.2, 13.8, 25, or 34.5kV. " and he said "it appears most of it is Y connected but older is delta."
I was merely pointing out that 11kV delta *does* exist and makes sense and is in use in other countries. I was just not automatically assuming that the OP was from the US and didn't know his supply voltages.

another
Works well too.. especially over ridiculously long distances.. Strangest-looking transformers you will ever likely see.
Cameron:-)
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Please tell me what SWER is. Thanx
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"Nukie Poo @verizon.net>" <vze32jp7<NO SPAM> wrote in message

Single Wire Earth Return. It's a system for supplying single phase power over very long distances using only one wire. :-)
Cameron:-)
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Are you serious? That sounds like an old telegraph setup. That doesn't sound too safe with the "return" current running through the ground like that. I remember reading in an old IEEE transaction about stray currents near the Brooklyn bridge causing severe corrosion problems (there's a power plant nearby on the Long Island side in Ravenswood). About 20yrs ago, I had a customer that complained about getting zinged when his foot was immersed in his swimming pool whilst the other was still on the ground. To make along story short, I wound up temporarily disconnecting his service drops to prove that his problem was caused by stray current and a utility issue (he had a private well so it wasn't coming in on any water main). SWER sounds like an invitation for such problems.
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"Nukie Poo @verizon.net>" <vze32jp7<NO SPAM> wrote in message

power
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in
prove
an
Interesting stuff.. stray currents can be a hassle and IIRC most old telegraph setups were two-wire DC (at least the ones here were)..
But to answer your question - yes, I'm quite serious. For more information, try a Google search on "Single Wire Earth Return". Happy reading!!
Cameron:-)
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Hmmmm, I must admit the SWER system has fascinsated me as well, it is quite unsual. I think it came about in the 50's as a cheap way to get power to a lot of farming areas, while there are problems with it, its better than no power at all. They dont use the system in the state I live in, its all three phase 22kV in the rural areas they actuall have power in. All the really remote places need their own generators. There are actually some 66kV distribution transformers not far from here, 66000/433 volts in one step!, they are pretty bulky looking pole transformers.
I think in western aus they use a neutral instead of the SWER system there, the place is really dry and sandy so Im guessing SWER was unreliable.
In suburbs here they did trial a distribution system based on the american one, single phase HV down each street, with small transformers supplying a few houses only. The secondry side was centre tapped 500v (to give a nominal voltage of 480/240). This is was an underground system, with the transformer primary being connected between an HV phase and neutral, pretty unusual system for australia. Interestingly enough they went away from that system back to the more common 3 phase distribution system again (415/240 secondaries with transformers 300-500kVA).
Seems to be a lot more variety in the american systems, must make it more interesting for the power distribution people.
cheers James
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I can imagine - I've seen a 34.5kV/480 3-phase bank and a 20kV/240-120 singlephase installation (the 20kV being derived from 1 leg of a 34.5kV line).
Dave
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You forgot one older service voltage - 2400V delta :) Not a factor though - these systems are probably as old as if not older than the 4kV wye systems mentioned by Charles...
Our municipal utility finally made the push last year to upgrade the last remaining 2400V lines to 13.8 kV (apparently culminating a 20+ years of transition)... yet the IOU that *also* operates here in town still has miles and miles of 4kV in use.
Dave
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as
Except that there usually are only TWO transformers used to provide the service. One BIG transformer for the 120/240 "lighting" and one "dogleg" to provide the third phase node.
It is very uncommon for secondaries to be connected in delta. A delta load is usually driven by a Y transformer bank.

With two transformers, it is VERY common for the service for larger restaurants. The distribution utilities seem to be pushing the 120/208 service over the 120/240/240/240 service described. They want the "balance" but the customers end up with inferior power for their heavy loads (208 v 240 volts).

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load
It is very common in the coalfields of West Virginia and Kentucky to have 480 delta, often with a "corner ground", but not always. Then they run the ground thru a resistor and monitor the current, if it exceeds a predetermined level, an alarm sounds and maintenance takes over.
Some mines even take 4160 into the mine where a unit substation reduces it to utilization voltage.
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yeah, and I left some out because the note was getting too long.

What is the correct terminology (and voltage ranges) for:
The high voltage stuff where (around here, northeast US) the wires hang from large insulators of many disks, usually on two large poles with a crossarm which support the cables, or latticework towers (older) with 6 conductors (two circuits I guess);
Circuits on single wooden poles, that have the crossarm below the wires but the insulators are not the bell-shaped ones seen on the primary lines running down the streets, and the insulators are rather large, they seem to run from large substations to small substations in rural areas to feed the local primary feeds, usually no neutral but sometimes it (or a lightning wire?) is at the very top of the pole, not half way down. These do not have transformers for individual houses, they just go substation to substation.

I have to admit I've never climbed one of these poles with a voltmeter! I can only guess from the occasional news story where someone gets electrocuted by coming in contact with an xx,xxx volt wire.
Also I often see setups where two poles are connected to each other with beams and 3 transformers sit on those beams. This is almost certainly to convert higher voltage primary to lower voltage (esp. since everything "downstream" of the setup is older looking), but within a few poles of this setup are two more transformers, each with 3 wires, one wire goes to the center phase and the other 2 go to one of the other phases on each side of an insulator spaced inline. Usually with a cable leading down the pole to a box at about eye level. Sometimes this setup exists in the middle of nowhere without the bank of 3 transformers. What is this? Mostly seen in rural NY in Niagara Mohawk territory. Seems redundant in the first case.
--
-Mike

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Substation to subtation = Transmission lines.....usually 120KV and up....to 750KV. Substation to transformer poles = Distribution lines....12,470 volts up to 35KV, depending on your utility.

Don't, you will never get close enough to measure the voltage before you are dead.

You may be looking at a capacitor bank, used for power factor correction on long lines. Common in rural areas. These do not provide power to any user.
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<snip>

Those are not stepdown transformers, they are voltage regulators. They adjust the voltage on the conductors.
Most lines with 2 poles per structure are either subtransmission or transmission. Most lines with a single pole are distribution but could be subtransmission or transmission.
Go here for a decent explanation:
http://science.howstuffworks.com/power.htm
Charles Perry P.E.
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The Scott Transformer system was also used on UK Distribution Networks, but you have to be aware of the history. Back in the days of old, electricicl energy was supplied from the DC power station in the town during the day, and at night, when the load was negligible, by a large battery. The battery was centre earthed, so running along the high street was a three wire cable. (Positive, Earth, Negative). And the towns residents were happy
As the electricity networks developed, Three-phase equipment was installed at the power station, and connections were made to an embryonic 33kV Grid.
The customers were connected to the AC system, using the old cables as two phases + neutral. The towns residents weren't too keen about having their High Street dug up just to install a different cable. Also these old DC cables were usually quite large cross sectional area, and in fairly good condition, being installed in an age when good engineering was over engineering. In order to achieve a balanced three-phase load on the high voltage system, the Scott Transformer was installed.
Having said the above, I'm not aware of any remaining in service. I believe that in the Croydon area, south of London we used to have such a network, but I think it was decommissioned back in the 1970's, before I joined the company. I do know of quiet residential areas where the old three core cables are still in use, but they have been cut up into short lengths, and used for cross road services and such like.
Peter Fisher - EDFenergy Networks Branch - CDM co-ordinator
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news:bkfddk$rc5

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...

It originally seems to be the other way around--according to IEEE Industry Applications Magazine, Nov/Dec 2002.
In March 1894, CF Scott said, In considering the marked advantage of the two-phase system for distribution and of the three-phase system for transmission, it occurred to me that a combination of the two systems night secure the advantages of both, and I have worked out a simple and effective method of accomplishing this result.
--s falke
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