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# understanding 12 wire generator diagrams

## understanding 12 wire generator diagrams

(OP)
Hi,

This is a probably a simple answer, but i don't understand. Im trying to understand converting a 3phase head, into a single phase head.

the question is based on these 2 diagrams

https://www.power-tronics.com/help/wiring-diagrams...

why can't Series Delta be used to create the voltage needed? is it because l1 and l2 are in phase? and would only measure out to 120v? or would they measure 0?

how do you tell by the diagrams which winding is in phase and out of phase?

sorry the newbie question

### RE: understanding 12 wire generator diagrams

Well, you can't believe everything that you read on the internet.
"Note: Single phase KW/KVA single phase ratings are approximately equal to 50% of the generator's three phase ratings"
Whoever wrote this has his head somewhere warm and dark.
Single phase KVA ratings are equal to exactly 2/3 of the three phase KVA ratings.
Single phase KW ratings are equal to exactly single phase KVA ratings. The PF becomes 100%

#### Quote (OP)

why can't Series Delta be used to create the voltage needed? is it Single phase KVA ratings are equal to exactly 2/3 of the three phase ratings.because l1 and l2 are in phase? and would only measure out to 120v? or would they measure 0?
You don't say what is "the voltage needed".
That is a common connection called a "Four wire Delta".
It will supply the 120/240 Volts single phase current.
It is generally used to supply a combination of 120/240 Volts single phase loads and 240 Volt three phase loads.
The connection is not used for single phase conversions because of reduced current available to 120 Volt, single phase loads.

The direction of the lines indicates the phase angle.
Parallel lines are in phase.
Lines drawn at 120 degrees displacement indicate 120 degrees phase angle displacement.

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

### RE: understanding 12 wire generator diagrams

(OP)

why is there reduced current for 120v? what indicates that?

### RE: understanding 12 wire generator diagrams

And again:
Well, you can't believe everything that you read on the internet.
"Don't use zig-zag if possible."
For many years, the zig-zag was the standard connection used for single phase conversion.
The three phase to single phase conversion may be done with the zig-zag quickly and easily by moving one winding end from the neutral terminal to any other winding end. The wire numbers may be dirty, illegible or even missing. Only a simple continuity check is needed.
Back to your question, reduced 120 Volt capacity.
In the series delta drawing, assume that the current rating of each winding is 100 Amps.
L1-L2 will supply 100 Amps at 240 Volts.
The windings, L1-L3-L2 will act as virtual winding with the same phase angle as L1-L2 (See Vector addition)
This virtual winding will Supply 100 Amps at 240 Volts in parallel with L1-L2
The total safe current available at 240 Volts is 200 Amps. (48000 VA or 48 KVA))
With a 120 Volt load, 100 amps will be supplied by the winding L1-N
100 Amps will be supplied by the winding combination L1-L3-L2-N
You may draw full current but the efficiency will be lower than with either the zig-zag or double delta connection.
100 Amps will be flowing through every winding.
With the double delta connection 100 Amps will be flowing in three windings.
With the zig-zag connection 100 Amps will be flowing through either two windings or 4 windings.
To anticipate your next question: 2/3 rating at single phase:
The series wye connection will support three 240 Volt circuits at 100 Amps each.
This will be 72000 VA or 72 KVA.
48KVA/72KVA = 2/3
With a 72 KVA machine at 80% PF, the prime mover will have enough power to develop 72KVA x 0.8 = 57.6 kW
When the machine is re-rated to 48 KVA, the output is KVA limited rather than kW limited. So kW may now equal KVA for 100% PF.

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

### RE: understanding 12 wire generator diagrams

(OP)
thanks Bill,

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