[TheForge] Fwd: Shop tools & layount (3-phase converter)

[theforge@mailman.qth.net]

Steve Smith wrote:

> The phase angles are fixed by the motor windings. The windings force 
> the three phases to be 120 degrees apart in a converter. There is no 
> way for  the converter construction to change this (assuming you are 
> using a 3 phase motor). You can change the amount of current flowing 
> through the third terminal by use of capacitors, but you cannot change 
> the phase angle. 


OK, after a lot of reading and thinking, I see you are right.   The bars 
in the rotor cut the flux of the three-phase windings of the idlers 
stator field,  inducing a counter electromotive force.  These voltages 
(seperated by 120 degrees due to the spacing of the windings) would 
affect the line voltages being passed to the load motor, at the very 
least as the union of the input(utility) wave and the induced wave.   I 
should have thought about this earlier as I have read before where  
three phase motors on three phase are designed to minimize the 
interaction of the phases through CEMF.    This would mean that  for 
optimal performance you would want a rotor with the bars running slight 
off of pure axial.     It is confusing reading the literature, since it 
all focuses on the generated third leg, generally stating that the first 
two are passed straight from the utility.  They are passed from the 
utility, but the converter has an effect on them.  Fitche's circuit 
maximizes this affect and cleans up the waveforms.   This also explains 
why additional motors on the circuit help matters as each of them is 
producing the same CEMF.   Well,  back to blacksmithing......

Charles