transformer controlled generator

[wiebe]

The motor on the gen is supplying 60 volts ac ,
2 of the diode,s is for the 12 volt batt charging output.

[Thob]

Bob,

I'm not a generator expert, but I do know a little about electronics.

I looked over your drawing for a while and couldn't figure out how it would work.  It appears that the more voltage the main windings produce, the more voltage would be feed back to the field coils, resulting in more voltage to the main windings.  Something has limit the voltage being fed back to field coils, or you will have a run-away over voltage condition.  I finally realized that the transformer must be setup with a saturated core, once the magnetic field saturates it won't go any higher, thus limiting the voltage in the field.  This would be adjusted by changing the air gap as you mentioned.

My point is this: the saturated core transformer will produce harmonics, just like a harmonic winding would.  Those harmonics are going to be on the generator's output; I have no idea how big they might be.  The only way to know for sure is build one and test it.

My other question relates to the term "stamford generator".  I've searched a couple of times, but I can't find a concrete definition of what people mean by that.  It appears that the stamford generator uses two stators and two rotors.  The stator on the exciter portion is feed with DC, producing a stationary magnetic field.  The exciter rotor then produces AC, which is rectified by diodes positioned between the two rotors; this produces a rotating magnetic field in the main generator which produces the desired output power in the main stator windings.  Power from the main windings is fed back thru a regulator to provide the DC for the exciter.  This typically consists of a step-down transformer, rectifiers, and a transistor control circuit that does the regulation.  The transformer in this case does not saturate, it provides a better match between the main winding voltage and what the regulator and exciter need.  Is this description accurate, or have I totally blown it?

[mobile_bob]

Thob

with this moving thing going on, i find my time quite limited for the forum
and would very much like to discuss this further, maybe next month?

check this out, as it has perhaps a bit more explanation

http://www.marathonelectric.com/generators/docs/manuals/GPN015.pdf

bob g

[Thob]

Bob - enjoy the move!  Hopefully, I'll still be kicking next month, so post again when you have time.

Thanks for the link.  Unfortunately, they didn't provide a schematic.  But it appears that a stamford type generator is pretty much what I described, EXCEPT, that the controller for the feedback to the exciter winding can be an AVR or a saturating core transformer.  From what they describe it sounds like what you're interested in will work.  I would be tempted to use 2 transformers like what ronmar suggested, one saturating core that sets the no-load voltage, and a second current transformer with multiple taps for adjustment of the full load voltage.  The secondaries of the two transformers could be put in series, then rectified to drive the field on an ST.

I'll still warn anyone who attempts this - you could destroy a gen head, or worse, if it doesn't work according to theory.  It would be good to have a way to quickly shut it down, better to have a generator test bench (3 phase motor driven by a VFD with a big red switch shutdown driving the generator).

[mobile_bob]

just a link to help another member on the lef

bob g

[Hugh Conway]

Hello all:
I was just given a Stamford Newage gen head. Data plate information:  F9348    240/120V  39/78A Mfg 11/80.
Don't know much about generators in general, So am looking for some help in identifying this unit.
Would this be considered a 10Kw generator? It is belt driven by a Lister SR2 (2 Vee-belts)
It appears to be one of the transformer controlled models, as it has no doghouse and was directly wired into a breaker panel. If anyone has information re this unit, greatly appreciated.
Cheers, Hugh