I have seen some distribution networks 'upgraded' by reconnecting the transformers from delta primary to wye primary, then changing the transformers feeding into the distribution from delta secondary to wye secondary. This simply raises the voltage by sqrt(3) on the distribution lines. Often insulators/fuses/etc... are rated to take the higher voltage anyway. Or they can be changed out to higher voltage rating equipment slowly over a period of time before reconnecting the transformers. If this can be done, then the same conductors can now carry more power without overheating.
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.
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
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.?
Just currious, what would the advantage of two phase distribution be? How common was three wire vs four wire distribution on two phase?
When I worked for a transformer shop, we used to make a fairly sizable transformer set for Scott T connection on a regular basis. It was used in a furnace were there were two sets of low voltage elements. I don't recall the details of the furnace exactly, but it would have been inconvenient to have three sets of elements. By using a Scott T connection for the feed, the equipment was a balanced three phase load but with only two element banks. When I first worked with two phase, I hadn't at first grasped that the power is constant for balanced loads. The voltages and currents do not sum to zero (instantaneously) so I think that's where I got the idea... but the instantaneous P and Q are constant for balanced loads. I had a UH, DUH moment when I realized that a two to three phase conversion with a balanced three phase draw couldn't happen in a transformer without a constant instantaneous P and Q level on the two phase side.
Is there any place with this sort of 2 phase at the meter? Also, has any place ever used (in the early days of AC electricity) any weird polyphase (something other than 3 phase, 2 phase or DC)?
PECO and Con Ed list 120/240V 2ø 5-wire in their 'service conditions' but not for new construction. At least one recent digitizing meter includes 2ø5w as a recognizable service form.
We used to call them a high leg or wild leg. They used delta connections on the xfmers. In the older sections of Phoenix there are still homes fed with
3 phase delta for the A/C's that was the only load in the house that used the 3 legs. They metered the two 120 legs and the high leg passed through the meter unmetered. Not even legal now. Not really available any more in Arizona as most new construction is all wye now. And the utilities are digellently removing all of the old stuff as they can force the customers into an service upgrade.
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