12 wire generator wired for single phase operation 1

[crthompson]

Gentlemen, I have been searching for information related to operating a 12 wire generator for single phase. I've found wiring diagrams but I can't find anything on the advantages/disadvantages of the different methods. I am specifically interested in power output and load balancing. Does anyone have any links or reference information they could point me to? It's basically just for research purposes and not for a specific application. Thanks in advance

 

[waross]

Both the Double Delta and the Zig-Zag connection work well. The Collin or Bar-diamond connection is a variation on the Zig-Zag connection. The Collin connection is specifically used to convert 10 lead generators to single phase. There is no need to consider a Collin connection for a twelve lead generator.
Advantage of the Double Delta connection is that it is symmetrical and looks better on paper.
The performance of the Zig-Zag connection is equal. The advantage of the Zig-Zag connection is ease of converting from three phase to single phase. Even if all the wire markers are missing or unreadable, a correctly connected generator may be converted from three phase to single phase with only a couple of simple continuity checks.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crthompson]

Thank you for the reply. I understand that there are two zig zag options. Could you elaborate on the advantages/disadvantages of each? Are the double delta and both zig zag configurations balanced? Are the power outputs the same? I have searched for hours and can't find what I'm looking for...

 

[waross]

Historically the Zig-Zag connection. Then the Double Delta became more common.
For either connection:
KVA capacity after conversion is 2/3rds of the original capacity.
kW capacity is 150% of the original capacity. Typically from 80% to 120% of KVA capacity.
Don't confuse the Zig-Zag grounding transformer with the Zig-Zag generator conversion.
I prefer the Zig-Zag connection because of the ease of conversion even without wire markers.
With all markers missing:
1> Arbitrarily label the outgoing leads as L1, L2, L3.
2> Open the neutral connections.
3> Find continuity from L2 to the neutral. For the lower voltage connections this will be two leads.
4> Reconnect the remaining wires to the neutral terminal.
5> The wire or wires removed from the neutral terminal and which have continuity to L2 are now connected to L3 and insulated.
You will have three wire single phase power from L1 to Neutral to L2.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[JohnMcNutt]

E=I²R heating is slightly less in a double delta than a zigzag.

Double delta has the in-phase windings slightly overloaded beyond nameplate if you are using the machine at 100% of rerated capacity.

Another connection available is high leg center tap delta so long as the 120 volt loads are reasonably balanced.

I have used all combinations including Mr. Ross's bar diamond and all are perfectly successful with no real practical drawbacks.

I prefer to use whatever connection is stickered inside the generator lid or order it the way I want it and let the manufacturer figure it out.

I have gotten a winding mis connected and noticed the engine lug when it should not have after being hard to excite. It is easy to get mixed up, that is why I prefer manufacturer's specified connections.

 

[waross]

kW capacity is 150% of the original capacity. Typically from 80% to 120% of KVA capacity.

I don't know what I was thinking when I wrote this.
kW capacity remains the same.
kW capacity depends on the prime mover power.
KVA capacity depends on generator heating and drops to 2/3 of the original rating.
The normal formula for power factor (kW/KVA) will show an apparent power factor of 120%.
Drawing 120 kW from a 100 KVA set does not mean over-unity.
It does mean overheating.

E=I²R heating is slightly less in a double delta than a zigzag.

Not so. At unity power factor the same current flows in all windings with all the connections.

I prefer to use whatever connection is stickered inside the generator lid or order it the way I want it and let the manufacturer figure it out.

It depends.
I agree for a new clean machine. Follow the nameplate, no warranty issues in the event of a problem.
For an old, dirty machine where lead numbering may not be clear, the zig-zag is safer.
You don't need lead numbers to convert to zig-zag.

I have gotten a winding mis connected

That is why I use the zig-zag connection on old machines.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[JohnMcNutt]

E=I²R heating is slightly less in a double delta than a zigzag.

Not so. At unity power factor the same current flows in all windings with all the connections.

I feel like we had this discussion before some time in the past. It is a very little think to nit pick about but here goes.

I don't know what book to find it in but I know from observation and measurement that the out-of-phase series windings will take roughly 1/3 and the in-phase winding will take roughly 2/3 of the parallel current in double delta.

A tiny bit of supporting evidence is that back in the 80s, Generac added an additional pair of in-phase windings to some machines. So the in-phase windings were 2x redundant. Then current division became 1/3 + 1/3 + 1/3. I have seen one of these units in person and have the manual somewhere.

 

[waross]

Consider the out of phase windings taken alone as an open delta. Assign an arbitrary load load and impedance.
The current will be leading at 50% PF in one winding and lagging at 50% PF in the other winding. If you do a vector sum of the voltage drops of the two windings you will find that it is equal to the voltage drop of the inphase winding.
Thus the in phase winding will share the current equally with the two out of phase windings.
Each winding has equal voltage and equal current so each winding has equal KVA. For a 100 KVA load, the load on each winding will be 50 KVA. KVA does not consider power factor.
kW considers power factor. For a load of 100 kW the in-phase winding will supply 50 kW and each of the out of phase windings will supply 25 kW for a total of 100 kW.
In the out of phase windings,, 50 KVA at 50% PF = 25 kW.
When a manufacturer shows both a three phase rating and a single phase rating, the single phase rating is always 2/3 of the three phase rating.
The rated current of a winding does not change. The in-phase winding still produces rated current.

Consider also that for use at the lower voltage, the windings may be broken into four groups.
For 120:240 Volt use:
Group 1 is a 120 Volt in-phase winding. (A phase)
Group 2 is a 120 Volt in-phase winding. (A phase)
Group 3 is two 120 Volt out of phase windings in open delta. (B phase and C phase)
Group 4 is two 120 Volt out of phase windings in open delta. (B phase and C phase)

For a zig-zag connection, group 1 is in parallel with group 2, and in series with that is group 3 in parallel with group 4.
When you put a 240 Volt load on the combination. The same current flows in both the in phase windings and in the open delta groups.
There is the same voltage drop across each side of the 120:240 Volts.

For a double delta connection:
Group 3 (open delta) is put in parallel with group 1. (in-phase winding)
and
Group 2 (in-phase winding) is put in parallel with group 4 (open delta).
As before, the same current flows in each winding.
There is the same voltage drop across each side of the 120:240 Volts.
The same division of current occurs when a single phase load is placed across one side of a delta transformer bank.
Anyone who has calculated the mixed single phase and three phase loading on a 120:240 volt four wire delta transformer bank should be familiar with these relationships.
The transformer bank loading calculations may be more interesting when the transformers are not the same KVA rating.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[JohnMcNutt]

I will be commissioning a new delta/single phase set in a couple months.

Calculations aside, I will see if it follows my empirical observation. If I remember this discussion by the time that all comes to pass. I have made the measurement several times since this came to my attention and it was always in the range of 2/3 - 1/3. Not precisely but within about 25%, sometimes precisely.

 

[waross]

The set single phase KVA capacity is 2/3 of the three phase KVA capacity.
So a 150 KVA set will safely produce 50 KVA per phase.
The 150 KVA set becomes a 100 KVA set on single phase.
How do you divide 100 in the ratio of 1/3 2/3 without loading one winding up to more than 50 KVA?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[JohnMcNutt]

Well I am back, as promised.

Stamford PI144K1 configured 240V high leg delta. Not using the high leg at this time, single phase 240 load connected across 2 corners only.

Methodology Fluke 381 with jaws on one set of windings and iFlex on another for space consideration and to allow easy switching.

Load during this test ~61A

In phase winding ~39A

Out of phase winding ~22A

I have made this measurement before on other delta connected sets with a Fluke 337, jaws only, and observed the same division of current, but not bothered to record.

 

[waross]

Interesting readings. Those readings somewhat defy the rules of vector addition but who am I to argue with Fluke.
Arguments with Fluke are almost as productive as arguments with furniture.

Bill
--------------------
"Why not the best?"
Jimmy Carter