3 phase types

[Charlie Bob]

All the 3 phase i've dealt with so far have been 120/208 wye services.
I've done quite a bit of research on the subject but i still would like to know a general idea as to the places the different types of three phase services are use.
I know the diference between them but i mean as whre can you expect to see a corner ground delta, or a open wye, etc.
Thank you all.:smile:

 

[charlie]

You are asking a very general question so I will give you very general answers.

1. 120/240 V, 3?, 4w, open delta - used around here for smaller 3? services
2. 120/240 V, 3?, 4w, full delta - used around here for larger 3? services
3. 240 V, 3?, 3w, corner grounded delta - not used around here but is normally used for 3? services in the western part of the country, especially for pumping. I believe this is mostly obsolete
4. 480 V, 3?, 3w, corner grounded delta - not used around here but is normally used for 3? services in the western part of the country, especially for pumping
5. 480 V, 3?, 3w, ungrounded delta - not used around here but is normally used for 3? services that need to be uninterrupted. By it being ungrounded, one phase can go to ground without tripping an overcurrent device. Maintenance may then be done on a scheduled outage or downtime.

There are a lot more and a lot of discussion may be had. Do you have a particular question about a particular voltage?

 

[480sparky]

There's a lot of good (or boring, depending on your level of entheusiasm) material here.

 

[masterinbama]

We have an old water system a few counties over that uses straight 480 3 phase corner grounded everywhere. The big problem is they use single phase panels and use the neutral bus for the grounded phase. Sent a guy to change a breaker one day and forgot to tell him this one important bit of info. Luckily I caught him on the Nextel before he got there. Told him to be sure and mark his wires because rotation was critical. (vertical shaft pump that would lose the impeller if started backwards) When he saw that it was fed with a 2 pole he called me and made a smart remark about how he knew he was just a 2nd year J-Man but I wasn't pulling no jokes on him like that. Do you know how hard it was for me to convince him that I wasn't pulling his leg about rotation.

 

[Charlie Bob]

That's good enough i guess. I just meant like where the different types are used.
like, what would you use at a supermarket. Or what is that is usually called for by engineers.
Or at a Factory, a gym ,a school, a church, etc.
i know it depends but i just wanted a general idea.
Thank you all.

 

[wirenut1980]

480 V, 3?, 3w, ungrounded delta - not used around here but is normally used for 3? services that need to be uninterrupted. By it being ungrounded, one phase can go to ground without tripping an overcurrent device. Maintenance may then be done on a scheduled outage or downtime.

Maybe not used in big city life, but used in several locations out in the sticks.:grin:

Charlie Bob, most services are wye. The most common places to see a delta service are old services for smaller industrial businesses and lift stations. In fact, the utility I work for does not build delta transformer stations for new customers anymore.

 

[jim dungar]

For new services, it seems very few utilities offer 3-phase in anything other than 480Y/277 and 208Y/120.

If the loads will be predominantly 120V, then a 208Y/120V service will not require step-down transformers. If there are many large loads, 480Y/277V usually means fewer amps drawn which may mean smaller conductors and/or less voltage drop.

 

[steve66]

I think most engineers prefer straight 3 phase Y systems, or single phase 120/240 volt systems.

Sometimes the power company will only run two lines of a three phase system to a certain area. Then, if you want 3 phase, they force you to use a Open Delta (which can be fed from just 2 lines.) It's either that, or the owner pays to run the 3rd phase wire several thousand feet.

Steve

 

[jim dungar]

I think most engineers prefer straight 3 phase Y systems, or single phase 120/240 volt systems.

Sometimes the power company will only run two lines of a three phase system to a certain area. Then, if you want 3 phase, they force you to use a Open Delta (which can be fed from just 2 lines.) It's either that, or the owner pays to run the 3rd phase wire several thousand feet.

Steve

3-phase systems always require a minimum of (3) conductors.
All delta connections requires all three phase conductors, although one of them may be grounded. An open-wye requires (2) phase conductors and the neutral conductor. I do not know of any multi-phase system that uses the earth as a 'primary' part of its return path .

 

[masterinbama]

3-phase systems always require a minimum of (3) conductors.
All delta connections requires all three phase conductors, although one of them may be grounded. An open-wye requires (2) phase conductors and the neutral conductor. I do not know of any multi-phase system that uses the earth as a 'primary' part of its return path .

Disregard the transformer marked bad. I have seen remote pump stations wired this way on purpose. Not very efficient but it does work.

http://insayne_kokane.tripod.com/electrical/transformers/sp3ph_delta_open_delta.jpg

Or this way in reverse.

http://en.wikipedia.org/wiki/File:Scott-T.JPG

 

[wireguru]

around here, the poco is a bit backwards. You only get 240 delta, unless you have your own transformer (large service) then you get 208Y120.

 

[LarryFine]

I do not know of any multi-phase system that uses the earth as a 'primary' part of its return path .

They're around, or have been. It's called SWER (Single Wire, Earth Return).

 

[jim dungar]

They're around, or have been. It's called SWER (Single Wire, Earth Return).

I have seen SWER.
What part of Single Wire relates to my statement about multi-phase systems?

 

[jim dungar]

Disregard the transformer marked bad. I have seen remote pump stations wired this way on purpose. Not very efficient but it does work.

http://insayne_kokane.tripod.com/electrical/transformers/sp3ph_delta_open_delta.jpg

Or this way in reverse.

http://en.wikipedia.org/wiki/File:Scott-T.JPG

Yes, an open delta only requires (2) transformers, but it still needs all (3) phase conductors.

The Wikipedia reference is actually to a Scott-Tee connection used with a 2-phase system (90? phase shift). It is subtly different than the Tee connection for 3-phase systems (compare the incoming line connections on the teaser unit) . And, a Tee connected transformer bank still requires (3) phase conductors on its primary.

 

[LarryFine]

I have seen SWER.
What part of Single Wire relates to my statement about multi-phase systems?

My bad. :roll:

 

[winnie]

An open delta bank requires three primary conductors; however one of those primary conductors can be the grounded conductor. See 'open-wye open-delta'.

In theory the grounded primary conductor could be the earth itself in an earth return system; however I don't know if this is ever implemented in practise.

-Jon

 

[hurk27]

Scott T transformers are used to supply a 2-phase load from a Polly phase system, it was a way to feed many old 2-phase draw Bridges that still had 2-phase motors.

Around here the 277/480, or the 120/208 is the norm in most commercial and light industrial, but in the bigger plants where they want reliability if there is a winding failure they use the 240 or 480 delta.

120/240 4 wire deltas are still around in older buildings but are being phased out (no pun intended)

 

[steve66]

Yes, an open delta only requires (2) transformers, but it still needs all (3) phase conductors.

The Wikipedia reference is actually to a Scott-Tee connection used with a 2-phase system (90? phase shift). It is subtly different than the Tee connection for 3-phase systems (compare the incoming line connections on the teaser unit) . And, a Tee connected transformer bank still requires (3) phase conductors on its primary.

You are correct, Jim, an open delta does still require 3 conductors. However, Winnie is also correct. The third conductor can be the grounded conductor. So the power company still gets away with only running 2 phases for a 3 phase system.

Open delta wiring:

http://www.dropshots.com/topgroove#date/2006-07-07/18:42:03

(Click the diagram to enlarge it)

Steve

 

[jim dungar]

You are correct, Jim, an open delta does still require 3 conductors. However, Winnie is also correct. The third conductor can be the grounded conductor.

In my other post, I had stated the conductor could be grounded.

... although one of them may be grounded.

So the power company still gets away with only running 2 phases for a 3 phase system.

A grounded phase conductor is still a phase conductor.

 

[LarryFine]

A grounded phase conductor is still a phase conductor.

In this case, though, while it is a circuit conductor, it's clearly not a 'phase' conductor; the primary is an open Y.