Corner Grounded Delta

[kwired]

Yes, I know that. I addressing this point you made:

In practical terms, that load could be also be supplied with just three conductors from a star connected transformer with the neutral connected to ground at the transformer.
I've seen it here in UK on industrial applications.

But with the wye secondary you have four points on the system no matter what. I suppose you could choose not to use the center point but it is still there and still common to all three phases.

With a delta secondary you only have three points. If you choose to ground mid point of one phase you have four, but there is no requirement to ground the mid point of one phase. The coils do not even need to have the center tap, main reason they usually do on pole mounted transformer banks is because they are made with same transformers used for single phase systems, which are always in stock in the POCO parts yard/warehouse.

 

[Besoeker]

But with the wye secondary you have four points on the system no matter what. I suppose you could choose not to use the center point

And then you would have the same merit you claimed for corner grounded delta.

You are not running a fourth conductor

Plus the additional advantage that, if you ground the neutral at the transformer, the voltages to ground are reduced.

 

[kwired]

And then you would have the same merit you claimed for corner grounded delta.



Plus the additional advantage that, if you ground the neutral at the transformer, the voltages to ground are reduced.

One probably could ground a phase of a wye system if they did not extend the common point and as far as end use is concerned you have the same thing as a corner grounded delta.

Reduced voltage to ground is the reason you don't find any more corner ground systems around here that are utility supplied.

The delta with mid point of one phase grounded still has one phase that is nearly same voltage to ground as phase to phase voltage though. 480 volt delta has wild phase voltage of about 415 volts to ground. These are still common wherever they use open delta for supply. If they are using all three primary phases it is always 480/277 Y.

 

[Besoeker]

The delta with mid point of one phase grounded still has one phase that is nearly same voltage to ground as phase to phase voltage though. 480 volt delta has wild phase voltage of about 415 volts to ground.

I've heard about that only because I've hanging around this place long enough.........

These are still common wherever they use open delta for supply. If they are using all three primary phases it is always 480/277 Y.

480, 277, 240, 120.........
We've been there before.

We have 400/230.
Simple and I like simple.

 

[Misha80]

Update

Update

For anyone interested.

Talked to POCO's regional office yesterday, the head of their engineering department is going to get all the info from the local office and see what happened. He wan'ts to see local guy's drawings for new service, I don't remember him even writing anything down, so that should be enlightening.

He told me they might install an open delta to get me what I need, and that a wye system wasn't what I really needed?

He didn't sound very happy when I told him their plan to fix the pole was to wedge blocks between my wall and pole to hold it straight. (Wall is split limestone aprox.150yrs old)

 

[kwired]

For anyone interested.

Talked to POCO's regional office yesterday, the head of their engineering department is going to get all the info from the local office and see what happened. He wan'ts to see local guy's drawings for new service, I don't remember him even writing anything down, so that should be enlightening.

He told me they might install an open delta to get me what I need, and that a wye system wasn't what I really needed?

He didn't sound very happy when I told him their plan to fix the pole was to wedge blocks between my wall and pole to hold it straight. (Wall is split limestone aprox.150yrs old)

How does he know what you need? If you have a lot of line to neutral load you lost 1/3 of the source just because it is the wrong voltage unless you provide your own transformation to be able to use the third phase. That is if the open delta is not corner grounded. If it is corner grounded you still have no neutral. He is trying to compromise. Open delta is going to cost POCO less and they will push for that.

 

[JoeStillman]

He told me they might install an open delta to get me what I need, and that a wye system wasn't what I really needed?

The POCO may not have all three phase legs available for the transformer primary. The primary on an open-delta secondary is often open-wye for that reason. If all he has is two primary phase legs, he can't make a wye secondary for you. I think 4-wire (high-leg) delta would be the best option if that is the case. Then you have A-N=120V, B-N=208V, C-N=120V, A-B, B-C & C-A=240V.

Check out this thread -> http://forums.mikeholt.com/showthread.php?t=54492

 

[kwired]

I've heard about that only because I've hanging around this place long enough.........


480, 277, 240, 120.........
We've been there before.

We have 400/230.
Simple and I like simple.

I think in general it is somewhat simple in most cities here in USA. If you want three phase you get 480/277 Y or 208/120Y. If you want single phase you get 240/120.

Now go to rural areas and such, POCO's do whatever to keep infrastructure minimized to a certain extent. That is where you run into open deltas more often, 480/240 single phase services and owner needs his own phase converter if three phase is necessary is also common.

How about in rural areas in Europe? Do they run any straight single phase primary distribution to farms or is there three phase everywhere, or even two phases and neutral to derive open delta systems. Maybe they can do open delta then another transformation to a wye is done on utility side instead of customer side.

 

[Besoeker]

I think in general it is somewhat simple in most cities here in USA. If you want three phase you get 480/277 Y or 208/120Y. If you want single phase you get 240/120.

Here, there is no "or". You get 400V/230V for LV three phase. Most residences get just the 230V single phase. All domestic appliances are fed with 230V. Lighting, wall warts, washing machines etc.

How about in rural areas in Europe? Do they run any straight single phase primary distribution to farms or is there three phase everywhere, or even two phases and neutral to derive open delta systems. Maybe they can do open delta then another transformation to a wye is done on utility side instead of customer side.

I guess it would depend on the size of the farm.
There are some single phase pole-mounted transformers for rural dwellings, small stores etc.

 

[kwired]

Here, there is no "or". You get 400V/230V for LV three phase. Most residences get just the 230V single phase. All domestic appliances are fed with 230V. Lighting, wall warts, washing machines etc.


I guess it would depend on the size of the farm.
There are some single phase pole-mounted transformers for rural dwellings, small stores etc.

The single phase transformers are 230 volt 2 wire I would assume?

 

[Besoeker]

The single phase transformers are 230 volt 2 wire I would assume?

They are, as far as I know. I don't live on a farm now, bit when I did, that's what it was.

 

[kwired]

Europeans can't handle all the extra information they need to remember for more than one voltage system:lol:

Sorry couldn't resist.

It would be simpler. It would also give even more qualifications to those that don't know what they are doing in the first place.

Funny thing is I find the NEC is much easier to follow for non dwelling installations anymore than it is for dwelling installations, yet dwellings is where the larger percent of non qualified installers do what they do, they have made it a market not worth pursuing. I don't turn down residential work, but don't make much effort to pursue it either.

 

[Besoeker]

Europeans can't handle all the extra information they need to remember for more than one voltage system:lol:

It frees up more brain cells to concentrate on the task in hand and make a better job of it rather than dealing with a plethora of voltage systems.....
Sorry couldn't resist. [/quote]

It would be simpler. It would also give even more qualifications to those that don't know what they are doing in the first place.

Actually, in recent years, qualification requirements have become quite a bit more stringent. Of course, that doesn't stop unqualified cowboys taking advantage of uninformed customers.

Funny thing is I find the NEC is much easier to follow for non dwelling installations anymore than it is for dwelling installations, yet dwellings is where the larger percent of non qualified installers do what they do, they have made it a market not worth pursuing. I don't turn down residential work, but don't make much effort to pursue it either.

We, at least my division, don't much domestic work either. Our customers are mostly industrial and the standard of work expected goes very much above and beyond the minimum legal requirements. You'll no doubt have seen some of the pictures I've posted.