Amperage output of generator

[I start fires]

he 'thinks' that is how it is wired, he has no manual or drawings
I believe the nameplate is correct
45 kw
120/208
1 ph

but who knows without opening up and looking at it

I did open it up. The leads are labeled T-1 through T-12 clearly.
They are connected exactly as the drawing shows.
Two 120 volt deltas joined at a corner.
They are however, larger gauge leads than I originally thought, more like #4's.
This is also an original owner machine. Nobody has ever tampered with it.
So you can put to bed the theory that it is wired differently than the drawing.
This removes one variable from equation.

 

[Ingenieur]

I did open it up. The leads are labeled T-1 through T-12 clearly.
They are connected exactly as the drawing shows.
Two 120 volt deltas joined at a corner.
They are however, larger gauge leads than I originally thought, more like #4's.
This is also an original owner machine. Nobody has ever tampered with it.
So you can put to bed the theory that it is wired differently than the drawing.
This removes one variable from equation.

I wish more posters were like you :thumbsup:
you follow up and answer questions, helping to narrow to a conclusion

 

[I start fires]

you are correct on the 1 ph pf rating issue, it is a bit confusing
although 1 ph can supply reactive power, most machines I looked at rate 1 ph at a pf = 1, go figure
but an older machine like this , who knows

the reason they give a pf is to give you an idea of how much reactive power the machine can supply and remain stable
0.8 should cover most motor loads under steady state conditions

the 120/208 is puzzling, I'd be curious as to what the mfg would have to say
#4 lead wire is good for ~ 200 A

That funny "208" is what triggered this entire thread.
Thanks again for walking me through this, I appreciate it.

 

[I start fires]

Here's another one.

Here's another one.



So here's another generator that I have.
I rewired it into a zig zag for single phase. Puts out 133/266 volt single phase. I'm not in love with the voltage but nothing seems to mind. The plate of course reflects a 3 phase connection.
Should put 94 amps @230 volts 3 phase and I believe it does.
The one thing I don't understand is what the 62 amps refers to on the nameplate.
Any ideas?

 

[GoldDigger]

One thing to keep in mind is that when a double delta is used to source single phase the current on the two terminals comes not just from one winding but from the parallel combination of the single winding and the series combination of the other two windings.
That, combined with the unused heat dissipation capacity, is why the available power to one phase is greater than one third of the three phase power specification.

Sent from my XT1585 using Tapatalk

 

[kwired]

Actually, I don't understand why generators are rated in a specific power factor at all. The load makes the power factor, not the generator. If I use this 45 KW generator to run nothing but electric heat and light bulbs, wouldn't I have a 56.25KW generator?

No you can still only power 45 kW. If the power factor is 1.0 then kW = kVA. If you had a 45 kW load with a .80 power factor the kVA is 56.25, the load on the generator (and the prime mover) is still 45 kW, you just have some excess current flowing that the unit is designed to be able to handle, that excess current isn't doing any work though.

 

[I start fires]

No you can still only power 45 kW. If the power factor is 1.0 then kW = kVA. If you had a 45 kW load with a .80 power factor the kVA is 56.25, the load on the generator (and the prime mover) is still 45 kW, you just have some excess current flowing that the unit is designed to be able to handle, that excess current isn't doing any work though.

What if I had a completely resistive load of 56,250 watts (245 amps) at 240 volts? That excess current would be put to work.

I never really thought about it before but the KW rating at .8 power factor is probably the limitation of the exciter windings more so than the limitation of the stator. If you were pulling 245 amps @240 volts but the power factor increased to 1.0, (assuming the engine had the horsepower) the stator would be fine but the exciter would probably fry.

 

[GoldDigger]

I thought that the excitation would only be increased slightly as needed to maintain output voltage as load, and therefore IR drop, increased.
Your description makes it sound as if the required excitation was proportional to the load.

 

[Besoeker]

Damn, you gave the solution with that post above!

Thank you kindly.
It's just a suggestion that makes sense of the numbers.

 

[kwired]

What if I had a completely resistive load of 56,250 watts (245 amps) at 240 volts? That excess current would be put to work.

I never really thought about it before but the KW rating at .8 power factor is probably the limitation of the exciter windings more so than the limitation of the stator. If you were pulling 245 amps @240 volts but the power factor increased to 1.0, (assuming the engine had the horsepower) the stator would be fine but the exciter would probably fry.

I'm with GD in that excitation current should increase to maintain output voltage, but won't necessarily be proportional to load. You still are loaded 125%, and if prime mover is rated same as the generator it is loaded 125% as well.

Heat given up by resistance of conductors and increased reactive current does give you some increase in real power which can be looked at as a decrease in overall efficiency. But we look at that as an inefficiency of the load not the source.