Re: stamford 3 phase Generator schematics and pictures, current limiting exercise

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Conner <steve@xxxxxxxxxxxx>

Hi Jim, all,

I looked at the schematic for the Stamford alternator. It seems to 
get its excitation mainly from its own output current by means of the 
regulator transformer, and relies on remanent magnetism to get 
started in the first place.

The output current in phase L1 flows through the H1...H4 winding on 
the regulator transformer, and induces a current in the X1...X4 
winding that gets rectified by CR1 and drives the exciter field. So 
the more current you draw, the more excitation the generator gets, 
and this counteracts the tendency of the output voltage to droop with 
increasing current draw. I guess it is assumed that the three phase 
currents are balanced.

The other input terminal of CR1 is connected to the excitation tap 
(S1, S2, S3 or S4) on the L1 stator winding. The effect of this as 
far as I can see, is that as the output voltage increases, the 
voltage from the excitation tap will partly cancel out the voltage 
from the regulator transformer and decrease the excitation, so 
helping to keep the voltage steady.

My first attempt at making it variable would be to take a small 120v 
variac and splice it into the wires that feed the AC inputs of the 
CR1 rectifier. I.e. disconnect the CR1 input from the regulator 
transformer tap (X2, X3 or X4), connect the regulator transformer tap 
to the 100% end of the variac winding, connect the 0% end of the 
winding to the excitation tap, and connect the variac brush to the 
CR1 input that you freed up in the first step.

Please note, this is only an idea that I'm mooting for discussion. I 
can't guarantee that it won't cause your generator to go unstable and 
leap round the yard like a bucking bronco. Maybe someone else with 
more experience of these things could comment?

Steve Conner
http://www.scopeboy.com/