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Low ZigZag single phase connection


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  #1  
Old 11-26-2012, 05:22:48 PM
grif grif is offline
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Default Low ZigZag single phase connection

Why is low zigzag the preferred single phase connection? Trying to wrap my head around the phasing, failing miserably.

Must be a bit of bucking on the open delta side? Otherwise it looks more like the low voltage taps would be considerably different?

Parallel winding groups I understand increase the current capacity of each of the 120 taps, I just can't see how it's balanced.

Double delta seems more balanced,,,
Or is the current a bit unbalanced in the double delta with the direct to load windings carrying a bit more than the ones in the delta?

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Old 11-26-2012, 08:24:43 PM
Jim Rankin Jim Rankin is offline
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Default Re: Low ZigZag single phase connection

The double delta, dog leg (what you're probably referring to as low zig-zag) and the zig-zag connection are all equivalent single phase connections.

As you see in the double delta connection, the two windings delta connected across each direct winding have the same voltage across, so the amperage should split approximately evenly between the two paths.

With the dog leg connnection, there's no direct winding across the open delta, but you can see that it is the same distance as it would be in the double delta, so voltage is the same across it. In this case the two windings in the open delta are in parallel, so amperage is equal between the two.

The dog leg is useful if there is any question about the lead markings. If you have a working 3 phase Y connection, you can easily go to the dogleg without even knowing any lead numbers. Essentially you break the neutral connection, find the two leads that are the other ends of any "line" pair and connect them to any other line pair. Insulate this splice, reconnect the neutral (now it's 4 wires instead of 6) L1 is one of the remaining "line" pairs and L2 is the other one.


With the zig-zag connection, you have only 4 windings in use and they are basically connected in two open deltas. The zig-zag is used to get 120/240 from a 10 lead generator.


---------- Post added at 06:24 PM ---------- Previous post was at 06:13 PM ----------

And I don't know who prefers the low zig-zag as they call it. Onan used the double delta in all the reconnection diagrams I have seen. This is the dog-leg connection as far as I am concerned, different from the zig-zag. I had never seen the real zig-zag connection before someone posted this page on the antique Caterpillar equipment page.
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  #3  
Old 11-26-2012, 10:10:42 PM
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Default Re: Low ZigZag single phase connection

Thanks Jim rankin I think I just can't understand those wiring diagrams yet.
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Old 11-26-2012, 11:50:34 PM
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Jim McIntyre Jim McIntyre is offline
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Default Re: Low ZigZag single phase connection

Quote:
Originally Posted by Jim Rankin View Post
...

With the zig-zag connection, you have only 4 windings in use and they are basically connected in two open deltas. The zig-zag is used to get 120/240 from a 10 lead generator....
I'm not quite following the Diagram B you posted. In order to get 120V between T9 (neutral) and T8, wouldn't the individual windings have to be operating at 69V?

Where'd this diagram come from?

Thanks!

Quote:
Originally Posted by grif View Post
...I just can't see how it's balanced.

Double delta seems more balanced,,,
Or is the current a bit unbalanced in the double delta with the direct to load windings carrying a bit more than the ones in the delta?...
Well... you used the word 'balanced'. What do you mean by that? Do you just mean that a 'balanced' connection has equal current through all windings (assuming the two 120V branches are loaded equally?)

Assuming so, then both Onan's double delta and low zig-zag are, as Jim Rankin stated, equivalent. And both would meet your definition of 'balanced'.

But, if you think of 'balance' as something more than just equal current in each winding, and require that each winding deliver equal power, then life gets more complicated, and neither connection (or any single phase-connected 3 phase set) will meet the goal...
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Old 11-27-2012, 09:35:23 AM
Jim Rankin Jim Rankin is offline
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Default Re: Low ZigZag single phase connection

Jim, the page is from Caterpillar service literature as in the old days, CAT sold very few single phase generators and have never personally seen a 12 lead 3 phase yet.

If it helps, the diagram after reconnection looks like a M.

If you look at the double delta schematic, leave off the base (windings T1-T4 and T7-T10 are not used) and then reverse the T3-T6 and T9-T12 windings.

Which must be done because there in a 10 lead reconnectable generator, there is a buried Y splice (T0 or N) made of T10, T11 and T12.

Jim, the voltage across the windings needs to be close enough that the magnetic characteristics of the generator end work and the regulator/exciter can safely deliver the field current required. But the main thing about all the single phase reconnections is to put the neutral exactly in the center of a single phase winding string instead of in the center of two of 3 phase windings to produce L-L = 2(L-N) voltages. Then if the voltage regulator has enough adjustment, it can produce 120/240.
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Old 11-27-2012, 11:24:19 AM
grif grif is offline
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Default Re: Low ZigZag single phase connection

Quote:
Originally Posted by Jim Rankin View Post
[/COLOR]And I don't know who prefers the low zig-zag as they call it. Onan used the double delta in all the reconnection diagrams I have seen. This is the dog-leg connection as far as I am concerned, different from the zig-zag. I had never seen the real zig-zag connection before someone posted this page on the antique Caterpillar equipment page.
I'm in trouble now. I was sure that diagram of the Low ZigZag came from one of the pdf Onan manuals, but it does not seem to be the case. Or at least I lost track of where it came from (I've also got it and another page that are different "looking" diagrams than that on page 20 of 900-0184). I just checked the wire "tags" from both the page with the Low ZigZag, and page 20, the tags in the diagrams both look to be the same phasing and configuration, which match my 15.0JC wire tags( or I think they do, looking at how it was configured when I got it).

Well,,, like so many other questions, answer one gain two more.
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Old 11-27-2012, 01:15:04 PM
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Default Re: Low ZigZag single phase connection

Quote:
Originally Posted by Jim Rankin View Post
...If you look at the double delta schematic, leave off the base (windings T1-T4 and T7-T10 are not used) and then reverse the T3-T6 and T9-T12 windings...
Interesting scheme that I'd not thought of before - Your only choice if you have a 10-lead set, I suppose.

I'd describe it as 2 wye connections, series connected, rather than deltas. Like shown in my attached picture. Delta would be 60 degerees instead of 120 as shown...
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Old 11-27-2012, 01:27:01 PM
grif grif is offline
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Default Re: Low ZigZag single phase connection

The most haywire scheme I came up with was just use each winding as a single 120 circuit.

Actually not sure why the folks that did the hack job on my 15JC didn't do that instead of what they did. Hope to get some time this weekend to mess with it a bit.
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Old 08-21-2013, 11:11:20 PM
CasaDelGato CasaDelGato is offline
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Default Re: Low ZigZag single phase connection

Thanks for the Zig-Zag and Double Delta diagrams. I'd seen people talking about those but couldn't find the diagrams.
I recently picked up a MEP006A genset, and am looking into what I need to do to get 120/240 single phase out of it.

The ZigZag looks easy enough - BUT I wonder about how changing the neutral connections around like that will affect the Excitation and Regulation of the unit. Does anyone know?

I've also realized that if I configure the set for 240/416, the midpoints of the 240's are available on the connection board - so I could possibly get my 120/240 off one winding that way. (Actually, I could get 3 sets of 240/120 - BUT all the loads connected to them would have to be completely isolated from each other, including NOT sharing a ground!)
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Old 08-21-2013, 11:21:27 PM
Jim Rankin Jim Rankin is offline
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Default Re: Low ZigZag single phase connection

(Actually, I could get 3 sets of 240/120 - BUT all the loads connected to them would have to be completely isolated from each other, including NOT sharing a ground!)

And THAT would get complicated!
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