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Scott35 Offline OP
Broom Pusher and
[Linked Image]

Wow, I looked at the first schematic and the text is really bad!! Got to do some serious changing around in AutoCAD for these and others!!

Anyhow, even though the text is only possible for ants to read, maybe we can discuss the schematics still.

This drawing is a detail of how a Delta would be connected as it's shown in the more familiar Triangle type pictorial - reflected towards a normal line drawing.
It also demonstrates how a 120/240 volt 4 wire closed delta would be made up using 3 separate single phase transformers [typical pole mounted bank].


Scott SET

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Oct 2000
Posts: 5,392
ok, 3 voltages here,
so it's a 208/190/120v D???
help me name it please.... [Linked Image]

Joined: Oct 2000
Posts: 2,722
Scott35 Offline OP
Broom Pusher and
Your on the right track!
The transformers used for this doo-hickey are plain 'ol everyday 1 phase "split coil" transformers - like the ones on poles for Residential service feeders.

Briefly, each transformer has "split coil" primaries and secondaries [if this is unclear, please see the schematic: "1 phase trans. schematic"" for explaination].
Primary voltage can be either 6000 VAC [connecting the coils in parallel], or 12000 VAC [connecting the coils in series additive].
Similar for the secondaries, except parallel connections are 120 VAC and series additive are 240 VAC.

Each transformer in this arrangement is wired in series additive [both Pri and Sec], so the input voltage is 12000 VAC and the output voltage is 240 VAC.

On the transformer winding at the base [bottom] of the traingle, is the center tapped neutral - making this a 4 wire closed delta.

Connected voltages available are:
120 VAC [L-N on ph. A and B only],
208 VAC [L-N on ph. C only],
240 VAC [L-L or L-L-L].

If the secondary coils were connected in parallel, and in this case the center tap would have to be removed [or we will let the smoke out of the windings [Linked Image]], the connected voltage would be:

120 VAC [L-L or L-L-L].

I have also drawn some schematics which are used to find relative polarity of transformers, plus effects of series connections [+ and -]. Along with these are some drawings of "Buck and Boost" autotransformers.

If interested, please inform. I'll see about posting them in this area too.

Scott SET - from the "Delta House" [Animal House].

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Oct 2000
Posts: 5,392
if the secondary coils were connected in parrallel, could it be corner grounded? ( i think that's somewhat discouraged, but for the sake of disscusion i'll ask)

aslo, all these pix are really neat, can i start simplistically by asking why this, or any other arrangement would be used?

pro's, con's of this vs. the Y setup?

[Linked Image]

This is good stuff Scott, better than crossword puzzles.

You didn't mention L-N in the parallel case. But it seems to me that there must exist a voltage with respect to the earth.

If you left the secondaries in series but eliminated the center tapped neutral what would the L-L voltages be? How about L-N (N being the utility's earth reference)?

What I expect is that L-L is 240 V and L-N is 208 V.

The explanation being that in this set up we are getting 240 V from two 208 V terminals 120 degrees apart instead of in the single phase case where we got 240 V from two 120 V terminals 180 degrees apart.

Am I close?
(If I am, then I definitely didn't understand something.)

Joined: Oct 2000
Posts: 2,722
Scott35 Offline OP
Broom Pusher and
Hi everyone,

I'm going to do some quick and dirty answers to stuff here, move on to the next one, and so forth.
Sorry for this, you just wouldn't imagine the work load that has been tossed onto me [Linked Image]
Between two - now possibly three bank branch projects where I need to do field installations [plus anticipate stuff, then note for As-Builts], I will be designing and uploading project notes and images to web pages, for all WAMU projects [this is typical for all of WAMU's contractors]. Each project is to be updated weekly.
Along with this, I am doing customer support / educated walk through on another project - which requires As-Built sets in several "Knowledge Levels" ?? -
And I still have two PCs to finish the reconfigs on [and their owners are calling every minute [Linked Image]].
Then I have memory upgrades at the Office on three W/S, plus install a few Apps - possible reconfig on one W/S.

Hardly any time to do fun stuff, like this forum!!, so please don't get too discouraged with me over the next 3 weeks if I don't respond to things right away - I'll make time to answer Qs and post images.

Anyhow, the Delta vs Wye connections have certain benifits according to the use of that system.
Deltas can handle Harmonics better [and even eliminate levels].
Wyes are best for multiwire systems, plus used to establish ground points [Zig-Zag transformers].
Capacitor banks are normally connected in Wye.

If the coils in the schematic above were connected in parallel [the split coils, that is], then the L-L and 3 phase voltage would be 120 VAC.
If one phase was grounded [AKA corner grounded], the voltage will still be 120 all around, plus 120 VAC to ground from the other two ungrounded phases.

If we leave the split coils in series as it's shown now - but remove the center tap and reground the system via one phase [once again , make it corner grounded like the 120 VAC setup], then the voltage will be 240 L-L and 3 phase, 240 VAC to ground from the other two ungrounded phases.

Each "Phase coil" in the delta is connected in parallel with the others. This eliminated the need to bring in 6 wires from the transformer, thus making the system 3 phase 6 wire [or 3 phase 7 wire when using a common neutral].

It still works as if there's 6 wires coming from the transformers - currents flow in the same matter.

This would work on preceeding setups - 3 phase 6 wire, 2 phase 4 wire, 1 phase 2 wire [a great way to visualize things].

On Wye systems, same thing goes - in their case, the "Phase Coils" are connected in series additive fashion, so the L-L voltage is 1.732 times the voltage of one single coil. Using the 3 phase 6 wire idea, one can visualize just how L-N load currents work out on the Wye system - because they do just that! [N should be best thought of as Common, so L-C is more correct].
L-C load currents flow from coil, to load in that type of matter.
L-L and 3 phase [L-L-L] loads go between individual phase coils, but L-C loads work from that certain phase coil - hence the fact that it's reather difficult to get the common grounded conductor in 4 wire Wye systems to balance like a 1 phase 3 wire's neutral will.

Got to go to the next one - 6 phase, then I'm off for today.

I'll post some connection schematics for 1 phase transformers, describing the various connections, plus I'll try for a 2 phase Tee schematic and Open Delta schematics - all according to what can be done and when [heard that before??---]

Scott SET

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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