open delta

[jim dungar]

But then, you won't have a center tapped secondary, either. Nor will you be supplying line-to-neutral loads.

The OP was about open-delta in general, you are the one who keeps bringing up 240/120 systems. Not every POCO service feeds line-neutral loads.

And they were open Deltas?

Yes, they are. Although all new services from our major POCOs are wye connections, the smaller "rural" ones are not as rigid.

 

[LarryFine]

The OP was about open-delta in general, you are the one who keeps bringing up 240/120 systems. Not every POCO service feeds line-neutral loads.

I keep doing that as part of the explanation. My bad.

Most people who work on 480v systems don't need this stuff explained.

 

[triplstep]

This link is one of my favorites when it come to distribution transformers. I've learned lots from it. It may take a bit to load for the dial up users.

Figure 15-19 gives a nice graphic.

http://www.mhprofessional.com/downloads/products/0071467890/0071467890_ch15.pdf

 

[mpross]

Protective Relaying

Protective Relaying

It is also used in certain protective relaying schemes such as distance relaying where you need a voltage reference. The broken delta connection comes in handy for this as a way to connect your PT windings...

 

[mpross]

Protective Relaying

Protective Relaying

...but I won't even try to explain here. I recommend the book by Blackburn. :smile:

 

[jrannis]

can anybody explain to me what an open delta system is and what is it used for? or at least link me to a website that does explain?

OK here it is one more time:grin:

http://forums.mikeholt.com/attachment.php?attachmentid=1122&d=1199625979

 

[peter d]

Here's an open delta setup with a 3 wire primary (no MGN present.) I don't know if the primary is delta or wye. This is SoCal Edison so if anyone know about their distribution system perhaps they can chime in on the characteristics of the primary, because I'm curious about it myself.

 

[LarryFine]

Here's an open delta setup with a 3 wire primary (no MGN present.) I don't know if the primary is delta or wye.

You should have shot the picture from the other side. :smile: It looks to me like both transformers are double-ended (i.e., line-to-line), and that both transformers' second HV bushings are in the shadow of the lower cross-arm.

It looks like (calling them A-B-C left-to-right) A phase hits the far bushing on both, making the primary also open-Delta. I see three conductors dropping, and what looks like a jumper through the left transformer's bracket.

 

[peter d]

You should have shot the picture from the other side. :smile:

I did, but I haven't uploaded them to photobucket yet.

They are indeed double bushing xformers, and the left most phase (A? C?) is connected to both of the bushings. So the primary connection is an open delta.

As you surmised there is a jumper across the secondary terminals. The load this is serving is a single well pump.

 

[ATSman]

Open Delta

Open Delta

Larry Fines explanation is excellent. It is a cost thing; using 2 single phase xfmrs to simulate 3 phase from a 3 phase source. Although the only time I have seen it used is in 3-phase sensing as in automatic transfer schemes for backup generators or in protective relay schemes using 3-phase sensing. I have not seen it used for anything other than control schemes. Can anyone say different as I would like to know?

 

[gar]

080921-0825 EST

tonytonon:

An open delta actually produces a three phase output, and thus I would not use the word simulate.

In our area there many uses of open delta for commercial applications. These applications generally have a lot of single phase 120 and 240 loads with a lesser need for 3 phase.

Our shop has such a supply. One large center tapped single phase transformer, and a smaller transformer to provide 3 phase. The whole building is about 40,000 sq-ft. In two of the spaces there are 3 phase CNC machines. We have 5 CNC machines and a number of other 3 phase machines. All the air conditioning is 3 phase. If our demand went up Edsion would simply add another transformer.

.