Amperage output of generator

[I start fires]

I have a 45 KW generator. I am trying to figure out how many amps each individual winding can handle safely without the thing lighting on fire.
Each winding makes 120 volts. 1t is a 12 lead machine which means that there are 6 windings.



The way I see it is 45,000 watts divided by 120 volts times .8 power factor = 300 amps (output of all windings at once)
Divide this by 6 windings = 50 amps per winding.

I have no clue why the name plate says 245 amps. Nor does it seem to specify at what voltage the 245 amps is at.
It's also curious why it says it's 1 phase while it's a 12 lead generator, and the voltage listed is 120/208. If anybody has any insight on this I would love to hear from you.

I have this machine wired in a double delta configuration for single phase; 120/240 volts (see schematic above)

That gives me (two) 3 phase 120 volt deltas connected together at a corner which makes the neutral. The way I see it; each delta can safely produce 100 amps@ 120 volts.

So I think I can safely pull 100 amps@ 240 volts or a total of 200 amps@ 120 volts (single phase).

To put it plainly, If the two single phase "hots" from the generator go through a 100 amp 240 volt breaker before the transfer switch, I should be good.

Does this sound reasonable to anybody here?
Thanks.

 

[Jraef]

From the way you have posted the question and described what you think you have, you are in WAY over your head. Your profile says you are an electrician, but I have my doubts. Even if true, you should not take on this project, it is apparently beyond your skill level and although we like to help people get over minor humps in their skill levels and experiences, you need a lot more that what can be done here. I suggest calling someone who knows what they are doing for this project and watching them, asking questions as you go. That's what apprenticeship programs are for.

 

[I start fires]

Could you elaborate on your conclusion?

 

[Jraef]

Could you elaborate on your conclusion?

The nameplate says exactly what you have and how it is rated, but you say you don't know why it says that. Then you decided, on your own, to connect it in a way that makes zero sense and will likely fry the generator and/or any load you connect to. Other than that, no problem...

I'm closing this thread before it turns into a public argument. I'll be open to appeals via PM, but on the condition that you offer some additional evidence to your being qualified to do this project.

I reopened it because you convinced me that you are an electrician. Sorry, but we get a lot of DIYers posting here and violating the rules.

 

[Ingenieur]

Couple things don't add up
first
P = S x pf, you mult power by pf, should be divided

second
S va = 45 kw / 0.8 = 56.25 kva and nameplate is rated 56.3 kva, ok
rated 208 x 245 = 50.96 kva or x 0.8 = 40.77 kw ????
Are losses/eff considered?

third
what are you trying to do?
you know the machine rating?
what does each coil matter?

 

[Jraef]

Your generator is rated for 245A at 208V, that's what the nameplate says, you cannot change that fact. A 208V system is 120V phase to neutral, so the windings must be configured in a Wye, with the Wye point going to ground. On a 12 lead generator there are two Wye windings, you connect them in parrallel and tie them together for one 3 phase output. Your 120V max current on each leg will be 1/3 of the 245A, so roughly 82A

Your idea to connect it in double delta corner grounded only works if you want to use it as a single phase generator. In that case you get 240 single phase between L1 and L2. Then 120V between either pole and the center tapped winding you have created. So you are sacrificing 1/3 or your capacity by not utilizing the other set of windings, therefore you must reduce the generator's capacity to 67% of what it says. So since it is 245A configured at 208V 3 phase, it will be the 163A at 240V and the 120V connections will each be 1/2 of that, so still, 82A max. The thing is, your AHJ may not accept this configuration if it is not explicitly shown on the nameplate. It's not that it isn't valid, I'm just saying from experience that some AHJs will not allow it, so be careful.

 

[Ingenieur]

Nameplate list 1 phase?
and if you take i x v x 1.732 >> 56.3 kva
???

 

[Jraef]

Nameplate list 1 phase?
and if you take i x v x 1.732 >> 56.3 kva
???

Oh you're right, I missed that.

 

[I start fires]

My point is that the nameplate is full of contradictions. It seems that some of you agree.

Some background on the machine:
This genset is as it was on the day it was manufactured in Appleton Wisconsin. Its 12 leads were connected at the factory in double delta for single phase use. This machine was never in its life configured to supply three phase power, although it could have been. It actually has an amp meter with a 3 position selector that you can switch between the 3 legs to see what the machine is pulling if it was set up for polyphase, it never worked since it was new in 1976.

You can wire a 12 lead generator with six 120 volt windings to be many things; 120/240 single phase (double delta or zig zag), 120/208 3 phase wye, 120 volt or 240 volt 3 phase delta, and I suppose 240/416 3 phase wye. I'm guessing the name plate has no clue how the 12 leads of the stator were ultimately connected at the factory. They were connected to accommodate the customer when it was sold. I did not rewire it nor do I have any intention to do so. It is staying as a single phase machine. I use it for power outages at my shop. I am in a rural area and have a single phase service.

It is my belief that this machine can supply 45KW in a 3 phase configuration, hence the designation on the name plate. It is also my suspicion that the way this machine left the factory it is only good for 2/3 of that because it's wired for single phase, although no info anywhere supports my suspicion.

What I don't want to do is smoke this machine. I am trying to figure out what the maximum amps I can draw before I cook the stator. This generator has no apparent over current protection. As I stated earlier, I have good reason to believe each of the twelve windings can handle 50 amps. If no winding pulls more than 50 amps, in my mind I can't hurt the thing. That means 100 amps @ 240 volts single phase output total in the factory wired double delta.

One more piece of info: This is more of a redneck observation than an egg headed one but the 12 leads from the stator look to be roughly #8 wire each so I don't see them carrying more than 50 amps each without getting a little too warm. This kind of supports my theory that 100 amps 240 volt single phase is all she's gonna give me.

 

[Ingenieur]

Imo the 45 kw is the correct 1ph rating
what hp engine?
how are the leads configured?
have you measured operating voltage?

 

[Jraef]

It's common for generator mfrs to do this because they don't want to make a bunch of different configurations, so above about 25kVA they use this re-connection of the 3 phase generator windings to give you single phase, even though it sort of "wastes" some of the capacity. What's odd is that in that configuration, the voltages should have been 120/240 single phase, not 120/208. So yes, given that one part of the nameplate doesn't look right, and the math doesn't seem to pan out, I'm suspicious of the whole thing, as in maybe someone re-worked it and put on a new nameplate?

You might want to run this up the flagpole at this company;
http://www.afconproducts.com/afconproductsservicesupport.html
They bought Kurtz and Root a long time ago, but still offered support on one I bought surplus maybe 7-8 years ago, even though I didn't buy a product from them directly. They were really nice about helping me out with a bearing issue.

 

[I start fires]

It has a 100 hp straight six diesel. Runs at 1800 rpm (4 pole rotor on the gen obviously) so that should spin a 45 KW no problem.
The generator absolutely does put out 120/240 volts, 3 wire (2 hots and a neutral) the way the leads are configured.
If it does in fact put out 45KW (which I doubt) it would have to make 150 amps @240 volts (.8 power factor)

Now if this is true, we would have to assume that the way the factory configured the 12 lead stator, it would be able to handle this.

Like I said, leads were configured by the factory, no one else.

Stator is wired in a double delta configuration. There is an image of this at the beginning of my thread.

Let's look at this like simple folk for a minute; each of the hots that leave the generator to power the load are connected to the corner of a delta or the point where two windings connect. Follow me so far? As I said earlier, those leads are 8 gauge wires. No matter how you slice it, 75 amps would need to come out of each of those 8 gauge wires to send the 150 amps to the load. That ain't happening my friend without smoke. That's the simple reason why I'm convinced this genset is not capable of putting out 45KW @single phase. Now if I rewire that stator's six windings to a doubled-up wye to get 120/208 and I'll get the whole 45 out of her no doubt. Problem is, 230 volt single phase motors don't really like 208 so that's no help.

 

[Ingenieur]

45 kw at 0.8 pf = 56.25 kva
56250/240 = 234 A
rating is 245

 

[I start fires]

It is strange. I posted this because the math on the name plate doesn't add up. I'm assuming this unit will make 45KW while wired in a delta or wye.

No no matter what I do, I can't come up with the 245 amps on the nameplate for anything.

Of course I am randomly picking and choosing what info on the plate I think is right while dismissing other values so this whole exercise is kind of flawed.

If I can figure what each winding pulls as a 3 phase machine, I can reverse engineer this to figure out the total output single phase would be.

 

[Besoeker]

What's odd is that in that configuration, the voltages should have been 120/240 single phase, not 120/208.

If each winding is 120V and it's connected as shown on the diagram shown by the OP, it would give 120/240V single phase.
Seems like and odd way to get it though. Maybe it was intended for use as a piece of test equipment with the flexibility of being able to be connected in different configurations for different output voltages. The double delta is just one of them. Having all twelve ends brought out might be a clue.

I wonder if the OP can say where his diagram came from?

 

[Ingenieur]

It's a std config but not an efficient one
http://manuals.chudov.com/12-Lead-Zigzag-Generator-Connection.pdf

it is a 100 hp engine ~ 75 kw
derated 33% for single phase ~ 50 kw
rating is 45 kw
my wag 75 kw 3 ph machine wired for 120/240 1 ph derated to 45 kw
I found this machine on the net rated 100 kw with a larger engine

 

[kwired]

Let's look at this like simple folk for a minute; each of the hots that leave the generator to power the load are connected to the corner of a delta or the point where two windings connect. Follow me so far? As I said earlier, those leads are 8 gauge wires. No matter how you slice it, 75 amps would need to come out of each of those 8 gauge wires to send the 150 amps to the load. That ain't happening my friend without smoke. That's the simple reason why I'm convinced this genset is not capable of putting out 45KW @single phase. Now if I rewire that stator's six windings to a doubled-up wye to get 120/208 and I'll get the whole 45 out of her no doubt. Problem is, 230 volt single phase motors don't really like 208 so that's no help.

Those conductors don't need to comply with NEC table 310.15(16).

The insulation probably is more then 90C rated, and the thing very well has cooling air flowing over it also. Without further details sounds like they likely could handle 75 amps.

I wasn't seeing how they came up with the 245 amps on the nameplate either

 

[I start fires]

Well it looks like some of my math was off. I now believe that I can get 156 amps @240 volts single phase; not just the 100 amps I previously thought.

This is a 45kw generator and the stator is wound with 3 pairs of windings; positioned 120 degrees apart. It's a 3 phase generator no doubt. I will only be able to utilize the entire wattage if wired for 3 phase. I don't want 3 phase so the question is how many amps can I pull wired for single phase.

A 45KW machine should produce 156 amps @ 208
45,000/ (208 x .8pf x 1.73)=156 amps

or the way I like to do it:

56,250 kva / 120volts / 3 phases = 156 amps per phase.

So each phase can pull no more than 156 amps. The stator would need to be wired in a double star configuration for maximum 120/208 3 phase output. That means that each phase consists of two windings doubled up. So if two windings in parallel can supply 156 amps that means that one winding by itself can only handle 78 amps.

No no matter how you wire this machine, this is a constant; the max output of any winding is 78 amps @ 120 volts.

The only way to get maximum available 120/240 single phase out of a 12 lead 3 phase machine is to wire it in double delta or low zig zag. Both are different but the end result is identical. In both cases the entire flow of 240 volt single phase leaves and returns to the machine by two windings. See attached schematics. If each winding can only handle 78 amps, that means the total 240 volt amperage must be 156. (78 x 2 = 156)

That 245 amps (continuous duty) on the nameplate is impossible wired in the factory connected double delta. That would mean that 122 amps would flow through each winding. Furthermore, the leads from the stator are 8 maybe 6 gauge wire. No way are you pulling that kind of amperage through those wires continuously.

Conclusion:
This machine can supply 156 amps @208v 3 phase.
or
156 amps 240v single phase.

That would be about 2/3 output at single phase vs 3 phase.

 

[Ingenieur]

The machine can supply 245 A 120/240 1 ph
the nameplate is correct
each winding handles ~1/2 of that ~125 A

the machine can produce 75 kw, 0.8 pf, 93.75 kva, 120/208, 260 A
or 130 per winding

Why assume 45 kw 3 ph (why over size the engine???)

do not confuse the windings with the lead ampacity

 

[I start fires]

The machine can supply 245 A 120/240 1 ph
the nameplate is correct
each winding handles ~1/2 of that ~125 A

the machine can produce 75 kw, 0.8 pf, 93.75 kva, 120/208, 260 A
or 130 per winding

Why assume 45 kw 3 ph (why over size the engine???)

do not confuse the windings with the lead ampacity

I assume 45kw 3 phase because
(1) the plate says 45 kw
(2) the only voltages listed are 120/208

Seems reasonable that the plate is trying to tell me that it is a 45 kw machine if it is configured for 120/208 volts.
I suppose it is possible that it is a 75Kw generator but the undersized diesel generator effectively makes it 45kw.
Does the nameplate take in to account the hp of the engine?

I'm just skeptical of 125 or 130 amps flowing down the same size wire that your electric range is hooked to. If the leads were 2 gauge wire I would have no problem swallowing the 245 amp output.

I know that chassis wiring amperage is rated differently, and of course there is a fan cooling the windings but this seems a little too ridiculous.

Maybe the wire can handle the heat but I would at least expect the electrical tape to melt off where the leads are joined if they're pulling 120+ amps.