# Parallel Wye to Double-Delta voltage problem



## chrisrappl (Jan 18, 2011)

After reviewing everything I discovered that:

Coil 1 was wrapped with T6, T12 / L3

Coil 2 was wrapped with T5, T11 / L2

Coil 3 was wrapped with T4, T10 / L1

Since I am now using L1 and L2, I swapped the control wires between Coil 1 and Coil 3 so that they are now sensing the lines in use.

No difference.

I'm pretty sure that I need to reduce the field current, but ...

If the voltage regulator is monitoring all three phases, and I now have no voltage on L3, it might be overcompensating. If it is measuring phase to neutral, I could try a jumper from L2 to L3.

If it is looking for a phase relationship, maybe I could extend a signal wire from either the T3,T5 splice or the T9,T11 splice. I'm not sure what the voltage would be.

If it is also looking for each phase to N, I'n not sure what that voltage would be from the T3,T5 splice to N.

I guess I need to break out the books (after blowing off the dust).


Thanks for any help. I don't really know who else I can contact for help with this.


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## micromind (Aug 11, 2007)

The 3 CTs are looking at current, not voltage. 

Where is the voltage regulator connected? Is it single or 3 phase?

Depending on the load, you might be better off connecting it series ∆ and not using the high leg. The disadvantage is the you could use only about half its capacity this way.


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## chrisrappl (Jan 18, 2011)

Micromind,
I considered a center-tapped Delta and a Zig-Zag or Dog Leg before deciding on the Double-Delta.
What I did not consider was the voltage regulator and its limitations.
I realize that the CTs are measuring current, but since this unit can be paralleled with other units and has synchronized controls, I don't know if it is using the CTs in the voltage regulator circuit to maybe measuring for droop? The truth is, I don't know anything about the voltage regulator and the way the wiring is managed, I can't trace the wires. I assume that it is measuring all three phases to each other and to neutral. 
My very limited understanding is that the voltage regulator receives AC voltage from the generator windings and rectifies it into DC to excite the field windings. The field voltage is probably around 60vdc and the field current proportionally controls the generator output voltage. The higher the field current, the higher the generator AC voltage.
Even though it is not a simple operation, the end result is that the voltage regulator monitors the AC output and controls it by varying the field current.
I'm debating whether to just restore the connections to original :crying: or investigate the option of installing a modern automatic voltage regulator.


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## gpop (May 14, 2018)

from a power tronic manual it looks like you use a single phase input (even on 3 phase) to the control board which is shown as hooked between a and c (1&3) as you are now using 1 and 2 you probably do not have one side of the regulator input hooked up so its sensing low voltage and maxing out the dc trying to get the voltage to come up. 

The ct's are most probably for a analog meter (display use only) and have no control on the generator (unless there's one for nesting with another generator or the grid which is a option that you are probably not using)

download the voltage regulator manual and you will probably be able to spot the problem


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## gpop (May 14, 2018)

chrisrappl said:


> Micromind,
> I considered a center-tapped Delta and a Zig-Zag or Dog Leg before deciding on the Double-Delta.
> What I did not consider was the voltage regulator and its limitations.
> I realize that the CTs are measuring current, but since this unit can be paralleled with other units and has synchronized controls, I don't know if it is using the CTs in the voltage regulator circuit to maybe measuring for droop? The truth is, I don't know anything about the voltage regulator and the way the wiring is managed, I can't trace the wires. I assume that it is measuring all three phases to each other and to neutral.
> ...


Don't over think it. The controller need to know what the output ac voltage is and it only needs single phase. It can not adjust independent legs so it doesn't need to know them.

If AC voltage is low it will increase DC which increase the mag field and causes AC to raise. On more modern ones it monitors the hertz and stuff for alarms. 

If its being nested then it has a ct to work out its load but yours should be jumpered on the board as it not being used that way. 

the extra ct's are for alarms or a simple analog meter on the generator to show you the amps.


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## chrisrappl (Jan 18, 2011)

Thanks gpop,
More to think about before I throw in the towel.
I don't think I can find a manual for the voltage regulator.
It was probably built to Western Electric specs. I believe it has markings for L1, L2 and L3, but I'm interested in finding out because if it only needs two phase conductors, I can give it that.
Update:
I just tried powering A & C with no joy.
The regulator board has T1, T2 and T3 identified, so I'm quite sure that it is looking for all three phases. 
Sorry for any confusion regarding Power-Tronics. The wiring diagram is just a generic drawing, not specifically for my generator.
I think I have three choices:
1) Rewire back to 120/208
2) Center tap Delta (don't know if the 120v capacity will be an issue)
3) Replace the voltage regulator


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## chrisrappl (Jan 18, 2011)

Thanks to everyone for their help.

Yesterday afternoon I went out to the shop, undid all my beautiful wiring and restored the connections to the original parallel Wye configuration.

I started the generator, adjusted the voltage and then ran it with a 12 KW load for an hour. I'm running at 211v phase to phase which gives me 120v A to N and 124v B to N once loaded. I'm sure having no load on C is affecting the difference in voltage. Testing with no load I can adjust to 208 phase to phase and read exactly 120v from each phase to N.

I know a lot more about this machine now, and I think I may go ahead and place an order with McPherson Controls for a replacement regulator, just to have everything on the shelf in case someday the original regulator fails (which it probably never will).

Now it's time to go out and clean up my mess in the shop.


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