12 Lead Generator

[iwire]

I have some experience reconfiguring a 3 phase generator from 208Y to 480Y or the other way around.

The other day I was off on a favor job, make this old three phase 20 KW generator work on this guys house. Now I expected I would be supplying the house single phase 208/120 leaving one leg unused.

Much to my surprise on looking at my diagrams I saw I could rewire for single phase 120/240 using what they called "double delta". Sure enough it worked fine.

Now the question, if I can make this '3 phase generator' produce single phase, is there a 12 lead motor that will run either single or three phase?

Go easy, I am not big on theory.

 

[crossman]

My first impression is that it wouldn't be possible for the motor. Single-phase 120/240 cannot create a rotating field in the stator of a three-phase motor, regardless of how it is wound or connected.

I would like to know more about the generator connections.

 

[iwire]

I would like to know more about the generator connections.

I will try to post the diagram.

Picture two deltas each made of 3 windings side by side.

Now slide them together till the bottom corners meet, that point is the neutral, the two outer bottom corners are the L1 and L2.

 

[iwire]

Here is how it arived

Here is what I changed it to

 

[crossman]

Sounds like it is a 3 phase high leg delta but not using the high leg? If you could post the diagram, I'd really like to see it.

Edit: Woah, that was quick! I'll check the diagram now.

 

[crossman]

Okay, that is pretty freaking cool. First, each winding is a 120 volt winding. They are taking two coils from a common phase and putting them in series. That creates 240 from end to end, and creates a centertap for the neutral. This would work without any of the other coils even connected, although capacity would be reduced.

Now, connecting all the other coils as shown is creating a 120 volt L-L delta on each side of the neutral. This simply adds to the current capacity of each leg.

Now, really there is still three phase being created in the generator, but we are only using a single-phase portion of it. The terminals at the tops of the deltas would show an out-of-phase condition to the other terminals.

 

[iwire]

Okay, that is pretty freaking cool.

I know it surprised me, it turned out to be just what I needed.

(Of course the old 3 phase 4 wire ATS they wanted to me to use was a no go)

Now, really there is still three phase being created in the generator, but we are only using a single-phase portion of it.

Ahh that makes more sense, the fact I was getting 120/240 was making me think single phase.

An odd thing is that the generators tag said 20 KW

It also said 60 amp 208Y/120 and 60 amp 120/240.

I set it up for 60 amps but it seems normally 20 KW at 120/240 would be better than 80 amps.

Is this 60 amp rating because of the odd connections?

 

[crossman]

That is what I was thinking... I would think the single phase power would be less than an actual three-phase arrangement. This is just an assumption on my part, an educated guess, intuition. I haven't put pencil or all that many brain cells to it as of yet. I was really hoping winnie or Mivey or Coulter or Rattus would wade in and tell us about it.:smile:

I am certain that a similar arrangement of a 12-lead motor fed by 120/240 would not start. However, there is something in the back of my head that says "if it works in one direction (generator) then shouldn't it work in the other direction (motor)?" But there is just no way it can! But wait a sec.... what about a split phase motor? Could this arrangement act like a split phase motor and actually start?

Ya know what, I think it might....

 

[iwire]

there is something in the back of my head that says "if it works in one direction (generator) then shouldn't it work in the other direction (motor)?"

That is what has been running in my head since I wired it.

Perhaps it wired as a motor it would work (with a push start) as a rotary phase converter and we would tie onto the 'unused' ends of the delta?

But I am really out of my depth and am just guessing.

 

[frenchelectrican]

An odd thing is that the generators tag said 20 KW

It also said 60 amp 208Y/120 and 60 amp 120/240.

I set it up for 60 amps but it seems normally 20 KW at 120/240 would be better than 80 amps.

Is this 60 amp rating because of the odd connections?

I done that all the time with 12 wire generators but however when you run in double delta set up like that and the 60 amp rating due the winding set up you are pretty much restricted to the winding rating due one set of windings is not used.

Very simuair to ZigZag connection transformer/ motor set up.

but the last thing i want to add here senice you mention 60 amp which on 3? you get full 20 KW but however with single phase you are only limited to 14~16 KW the most unless that generator do have extended stack then it can take full 20 KW rating.

Merci,Marc

 

[mivey]

I just noticed this thread and find it interesting. Just as a first thought:
Using iwire's info, the generator is a 20 kW or a 25 kVA unit with 120 volt coils. Also 25 kVA/sqrt(3)/0.240 kV = 60.14 amps. So good so far because it matches the specs from iwire.

Based on the diagram showing 6 coils, let's deduce that each coil is good for 25/6 or 4.17 kVA. But what does that mean for the double delta? I am going to think about single phase loads on a delta bank.

In a closed delta with equal impedances, the lighting coil carries 2/3 of the single-phase load. This means you are good for 6.25 kVA of single phase load. This is 6.25/0.12 = 52 amps.

Here is the interesting thing: I would think they would have a 50 amp rating at 120/240, not a 60 amp rating. Unless it is really a 28.8 kVA or 23 kW generator.

Still a nifty generator.

 

[mivey]

Oops. Late night math.

25 kVA/sqrt(3)/0.208 = 69.39 amps which is more than the 60 amps given. If we are going to suffer this kind of de-rating (60/69.39 = 86.47%), then following my prior logic, the single phase 120/240 rating would be 52.083 * 86.47% = 45 amps.

Still seems odd for now, but I'm going to quit for the night.

 

[quogueelectric]

I have some experience reconfiguring a 3 phase generator from 208Y to 480Y or the other way around.

The other day I was off on a favor job, make this old three phase 20 KW generator work on this guys house. Now I expected I would be supplying the house single phase 208/120 leaving one leg unused.

Much to my surprise on looking at my diagrams I saw I could rewire for single phase 120/240 using what they called "double delta". Sure enough it worked fine.

Now the question, if I can make this '3 phase generator' produce single phase, is there a 12 lead motor that will run either single or three phase?

Go easy, I am not big on theory.

I am sure you could use this extra leg to drive some sort of emerg bat voltage inverter system on an emergency gen system just like you would set up a gentran system otherwise this odd leg will go unused and that would be a shame on a nice sized generator like this.

 

[quogueelectric]

Upon further review I see I totally missed your question and in my opinion I dont think you can. The basic theory of a 3 phase motor is a rotating magnetic field which the rotor chases with a magnetizing current establishing magnetic poles that chase the rotating field around and around ect ect........ verry efficient few moving parts. I wish I could afford a generator that big to run the whole neighborhood.

 

[quogueelectric]

Upon further further review the copy of the diagram shows only 2 of the 6 windings are being used at the 120/240 setup I think you could run almost any equipment in a house 240 at 208 without much of a problem most 240 loads are heating elements which just follow ohms law. It is a shame to be wasting the power of all 6 windings.