# Thread: 6 phase forked star secondary wound transformer

1. Originally Posted by RogerRoger25
The secondary line voltages but I would like to see the full method if possible?
Your thread title says 6 phase secondary. 9 secondary windings do not correlate with a 6 phase output. You can get 60 degrees separation utilizing a dual delta to wye configuration because it has an inherent 30-degree phase shift.

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Originally Posted by Smart \$
Your thread title says 6 phase secondary. 9 secondary windings do not correlate with a 6 phase output. You can get 60 degrees separation utilizing a dual delta to wye configuration because it has an inherent 30-degree phase shift.
This is the phasor diagram;

3. Originally Posted by RogerRoger25
This is the phasor diagram;

FWIW, the primary phasor diagram does not correlate with the primary winding depiction.

Your secondary winding voltages will be VPRI·SEC:PRI turns ratio. The magnitudes of Vhn, Vgn, and Vin, i.e. the short phasors, correspond to the calculated result. The remaining six will have a magnitude that is 1.732 times that magnitude. The angles will be as depicted (0° being to hard right).

4. Originally Posted by RogerRoger25
This is the phasor diagram...
Looking at it again, a couple secondary phasors do not correlate properly with the depicted winding configuration. Here is a corrected diagram...

Last edited by GoldDigger; 03-17-17 at 05:54 AM.

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Smart\$, I think that you have linked to a Google-based image that is not visible to other users.

6. Originally Posted by GoldDigger
Smart\$, I think that you have linked to a Google-based image that is not visible to other users.

This any better?

FWIW, looking at the diagram even yet another time. The polarity dots on the secondary windings seem to indicate the secondary phasors are pointed the opposite direction of where they should. Can anyone confirm?
Last edited by Smart \$; 03-17-17 at 08:48 AM.

7. Originally Posted by Smart \$
Your thread title says 6 phase secondary. 9 secondary windings do not correlate with a 6 phase output. You can get 60 degrees separation utilizing a dual delta to wye configuration because it has an inherent 30-degree phase shift.
There are six line to neutral terminals.

8. Originally Posted by Besoeker
There are six line to neutral terminals.
At the point I wrote that I was not aware he was wanting to use the triple-wye secondary...

9. Originally Posted by Smart \$
At the point I wrote that I was not aware he was wanting to use the triple-wye secondary...
No problem.
I just don't know what it would be used for. I have the J&P transformer book. It's 800 pages and no mention of such an arrangement. It looks like three zig-zags connected together. I'd be interested to hear if anyone can cite an actual application where one has been installed. And why.

10. I'm pretty sure saw it used once a long time ago as a way to have one large main transformer feeding multiple low voltage three and single phase loads to large IBM main frame computers (back in the day). Old IBM main frames used to use 415V 3 phase for the computer power supplies and 240V single phase for the fans and coolant pumps inside. So looking at those vectors, the large vectors would give you 2 sets of 3 phase 415V: a, c, e and f, b, d, then 3 connections for 240V single phase loads: h-n, g-n and i-n. I can imagine they did that for better balancing of the loads?

The thing is, computers aren't built that way any more and those that were are museum pieces now, so it's highly unlikely that anyone uses this any longer. The only reason I saw it at all was because I helped scrap an old IBM mainframe computer from a hospital in the late 70s and that transformer was fascinating to me, so I looked it up. I never actually knew the voltages at the time, it was already apart when I saw it, but I learned years later that IBM had used 415V for the power, and I knew from that scrapping job that all the fans and pumps were 240V single phase, because we used them for different things, so I'm putting 2 and 2 together as to what was going on. Seeing this diagram now that I know more made me realize that's what I had seen.

The transformer was I think around 150kVA, which if you think about the fact that my iPhone probably has as much computing power as that beast did back then, is pretty amazing. We stripped it for the copper, I think we got something like \$25 for it at the time... We stripped out all the PC boards and sent them to a refiner, got back a little over 8 ounces of gold, but as I recall, we had just gone off of the gold standard a few years earlier and got something like \$120/oz. Wish I had just kept it...

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