Why use WYE in residential apartment buildings

[Hv&Lv]

Not familiar with the standards for drawing transformer coil arrangements, here's a textual description in case that helps:

For a 3 phase primary supply, you have 3 available voltage sources that are 120 degrees apart. Then you use (3) single phase transformers that have center tapped secondaries, one on each of the 3 primary voltage sources, to get (3) 120/240V services that are also 120 degrees apart. Connect all (3) center taps and earth that point. You now have (6) different L-N waveforms, 120V in magnitude, with the pairwise phase shifts comprising all multiples of 60 degrees. Which I guess we are calling hexaphase, although I would still say it is a 3 phase system. [Just as 2-phase has (4) different L-N waveforms, each 90 degrees apart.]

Cheers, Wayne

Why you just described a wagon wheel!

 

[kwired]

Not familiar with the standards for drawing transformer coil arrangements, here's a textual description in case that helps:

For a 3 phase primary supply, you have 3 available voltage sources that are 120 degrees apart. Then you use (3) single phase transformers that have center tapped secondaries, one on each of the 3 primary voltage sources, to get (3) 120/240V services that are also 120 degrees apart. Connect all (3) center taps and earth that point. You now have (6) different L-N waveforms, 120V in magnitude, with the pairwise phase shifts comprising all multiples of 60 degrees. Which I guess we are calling hexaphase, although I would still say it is a 3 phase system. [Just as 2-phase has (4) different L-N waveforms, each 90 degrees apart.]

Cheers, Wayne

After more thinking about this one, wouldn't it be simpler and probably less cost to just use three 2 pole "mains" and supply them from three single phase transformers - only will matter to POCO if they are balanced across the three phase primary or not, will still function the same to the end user

 

[xptpcrewx]

I know that it is common to use two legs of a 208/120V three phase service to create 'single phase' service for apartment buildings.

I am curious as to why this is done.

It would seem to me that the individual residence is better served by a 120/240V single phase service, and that the large collection of residences could be served by three single phase supplies.

If a single 'service' is required, or of 'house loads' such as elevators require 3 phase, then a 'hexaphase' system would fit the bill, providing 120/240V for residences and 208/120V for 3 phase loads. Phase current for the same total kVA would be halved, possibly reducing available fault current.

Just a random musing thinking about @Tainted project.

Jon

I don't know the answer but I would imagine its just easier and more efficient use of the transformers kVA (than only partially loading half a winding for 120-V loads). Let me know what you find out.

 

[wwhitney]

So you have a main switchboard/panelboard with 6 ungrounded buses and a neutral bus?

This does seem to the be the sticking point to me. I guess you could have a 6 pole fused disconnect, and then taps on the load side to 5 different main breaker panels: (3) 120/240V panels for the (3) different single phase subsystems, and (2) 208Y/120V panels for the (2) different 3 phase subsystems. Then each of those panels can have breakers/meters for the various apartments and 3 phase loads.

Cheers, Wayne

 

[electrofelon]

I actually really hate the 120/208 wye system. 240 is already too low IMO, but then you go with a wye where you want the 120 and now it's even lower. Too bad the man squashed the 120/240 delta system, I always kinda liked that.

 

[mbrooke]

I actually really hate the 120/208 wye system. 240 is already too low IMO, but then you go with a wye where you want the 120 and now it's even lower. Too bad the man squashed the 120/240 delta system, I always kinda liked that.

The most ideal system for me is 139/240Y, no line to neutral loads. I don't understand neutral conductors for one thing. Love it for so many reasons I could crash the server.

The most practical and efficient system however would be 240/416Y. 240 for single phase loads, 416 for 3 phase motors and heaters.

I'd love to have a lab and research the practicality of having 400 volt consumer goods just so I could dispense the noodle, but for all I know 400 volt might be to high to be practical for small items.

 

[yuhong]

The most ideal system for me is 139/240Y, no line to neutral loads. I don't understand neutral conductors for one thing. Love it for so many reasons I could crash the server.

The most practical and efficient system however would be 240/416Y. 240 for single phase loads, 416 for 3 phase motors and heaters.

I'd love to have a lab and research the practicality of having 400 volt consumer goods just so I could dispense the noodle, but for all I know 400 volt might be to high to be practical for small items.

127/220V is already common in downtown network areas and the like.

 

[drcampbell]

Can you draw that out for me, I am not getting how that connection would work?

 

[mbrooke]

127/220V is already common in downtown network areas and the like.

True, as well as South America. Nice system to have.

 

[retirede]

The most practical and efficient system however would be 240/416Y. 240 for single phase loads, 416 for 3 phase motors and heaters.

I agree - This is essentially what Europe has.

 

[winnie]

The most practical and efficient system however would be 240/416Y. 240 for single phase loads, 416 for 3 phase motors and heaters.

As a long term upgrade to the electrical system, I think this would make a lot of sense.

Lots of the 120V devices used by Americans are actually universal voltage and will work just fine at 240V.

Lots of large equipment currently used on 480V systems will work just fine at 416V.

Still lots of things would need to change to make this a reality.

Jon

 

[mbrooke]

I agree - This is essentially what Europe has.

And most of the world. Eliminating 480-208 transformers alone substantially reduces losses.

As a long term upgrade to the electrical system, I think this would make a lot of sense.

Lots of the 120V devices used by Americans are actually universal voltage and will work just fine at 240V.

Lots of large equipment currently used on 480V systems will work just fine at 416V.

Still lots of things would need to change to make this a reality.

Jon

Bingo! You see it! Most 480 volt motors will do fine at 416 volts and lots of devices like Ballasts are already universal voltage.


Consumer good will have to change, but once you try a 3000 watt appliance you do not go back.

OCPD and panelboards will have to get re-listed and this is where UL standards need to "get real".

 

[kwired]

I actually really hate the 120/208 wye system. 240 is already too low IMO, but then you go with a wye where you want the 120 and now it's even lower. Too bad the man squashed the 120/240 delta system, I always kinda liked that.

The 120/240 delta is not gone. Some places is maybe almost non existent but if you really like them come out to where I am, they are still everywhere and still installing new services with them. Most the new services are on farms or light industrial where they have lot of motor load and not so much 120 volt loading.

 

[electrofelon]

The 120/240 delta is not gone. Some places is maybe almost non existent but if you really like them come out to where I am, they are still everywhere and still installing new services with them. Most the new services are on farms or light industrial where they have lot of motor load and not so much 120 volt loading.

Awsome, Im packing my bags now!! I run into tons of them in Seattle, but I dont think they will let you install a new one. Here back east quite a few of them too, but as far as I know the POCOS also wont let you install a new one (I know national grid doesnt, not totally sure about NYSEG).

 

[winnie]

The most practical and efficient system however would be 240/416Y. 240 for single phase loads, 416 for 3 phase motors and heaters.

Thinking about 'how to transition to 240/416Y' I think I came up with a hybrid system that clearly has unmarried parents.

Construct a 416Y system from 240V center tapped transformers, and bring out the center taps to serve 120V loads. Residences would be served with 120V L-G and 240V L-G. 416Y would be available for large 3 phase loads.

*tongue firmly in cheek*

-Jon

 

[kwired]

Thinking about 'how to transition to 240/416Y' I think I came up with a hybrid system that clearly has unmarried parents.

Construct a 416Y system from 240V center tapped transformers, and bring out the center taps to serve 120V loads. Residences would be served with 120V L-G and 240V L-G. 416Y would be available for large 3 phase loads.

*tongue firmly in cheek*

-Jon

You should be able to tie to all three center taps to supply an existing 208 volt three phase load as well.

Too many such circuits overloads the inner half of the wye windings though and no really good way to balance out the outer half other than with 120 volt loads - but they would be two ungrounded lines instead of an ungrounded and a grounded conductor.

 

[Frank DuVal]

Not familiar with the standards for drawing transformer coil arrangements, here's a textual description in case that helps:

For a 3 phase primary supply, you have 3 available voltage sources that are 120 degrees apart. Then you use (3) single phase transformers that have center tapped secondaries, one on each of the 3 primary voltage sources, to get (3) 120/240V services that are also 120 degrees apart. Connect all (3) center taps and earth that point. You now have (6) different L-N waveforms, 120V in magnitude, with the pairwise phase shifts comprising all multiples of 60 degrees. Which I guess we are calling hexaphase, although I would still say it is a 3 phase system. [Just as 2-phase has (4) different L-N waveforms, each 90 degrees apart.]

Cheers, Wayne

No, I need a drawing, as what I read seems like a short, or hanging loose transformer leads. If I connect the center taps together, then they are three autotransformers?

OK, saw the wagon wheel. That is three autotransformers! And the windings of the transformers are unequal above and below the middle (cannot call it center point anymore, as it is not center). OK, center is center of the wagon wheel, just not center of the transformers, thee legs are longer than the other three legs. More of a snowflake than a wagon wheel now. Still three phase, as there are only three sine waves. You could say the polarity switches 180 degrees as your perspective changes, but it is the same sine wave, just different voltage.

 

[wwhitney]

OK, saw the wagon wheel. That is three autotransformers! And the windings of the transformers are unequal above and below the middle

See post 28 above for a better drawing. The "wagon wheel" is just the secondary and doesn't show the primary.

They are still isolation transformers; only the center points on the secondary are interconnected. And on the secondary, all the unit length coils, the 6 spokes of the wheel, so to speak, are the same.

Cheers, Wayne

 

[mbrooke]

Thinking about 'how to transition to 240/416Y' I think I came up with a hybrid system that clearly has unmarried parents.

Construct a 416Y system from 240V center tapped transformers, and bring out the center taps to serve 120V loads. Residences would be served with 120V L-G and 240V L-G. 416Y would be available for large 3 phase loads.

*tongue firmly in cheek*

-Jon

Can you draw this up? Or what the panel might look like? I like your idea.

 

[winnie]

Please keep in mind that this is something of a random musing thread, not something that I will ever implement.

The 'wagon wheel' does not use autotransformers; it uses a true isolating transformer arrangement. It is IMHO a 3 phase arrangement, but each phase has a full 120/240 center tapped secondary, allowing one to supply each apartment with 120/240 single phase rather than 120/208 pseudo single phase. This is no different than having 3 separate blocks each with their own single phase 120/240V transformer on a different distribution phase. The potential benefits are that the building presents a balanced 3 phase load to the utility, but with half the current on the 120V 'legs'. The customer sees a standard 120/240V. The downside is increased complexity, and possibly lower 'diversity' on each phase, since with a 120/208V system each phase is connected to more apartment feeders.

Here is the transformer diagram:


The idea of a 'transition circuit' to 416/240V (where each residence just gets a single phase 240V L-N service) is to provide a hybrid system where each phase provides both 120 and 240V, but as L-N voltages, not standard split phase L-N-N 120/240V. Presumably the bulk of the loads (including receptacles) would be directly supplied with 240V (in the European fashion) but there would be a few 120V receptacles available.

The transformer diagram for this is:



-Jon