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Re: FW: Initial setting for sync phase angle on an RSG



Hi Colin,

Thanks for your Spice data (even though it wasn't the .sch file, I was able to
open up your file in a text editor and extract your values for LShift, Rshift,
etc... I plugged them into my Spice and got similar results, however, my net
shift could only get to about 25 degrees. I then looked at your values for the
LMotor, RMotor and plugged my own in (R is 24 and L I'm guessing about 2H.
Anyway, I then observed your variac value which appeared odd to me. I found my
notebook and found that I had recorded my 30A ballast variac for the pig.
It was
11.2mH at 1/2 setting. I was planning on using my 10A variac for the motor
phase
variation and guessing it would be near 10mH at full. Plugging in those values
allows zero phase shift.

I then began playing with Spice. I did achieve a phase shift, however, I
altered
things a bit. What I did was put in a 24 ohm resisotor parallel with the motor
(just to give it the same value of the motor) and then put in series with this
resistor a cap at 100uF. This RC is in parallel with the motor (LMotor and
RMotor) and after the variac which is in series with the motor. I was able to
achieve decent phase shifts as I increased/descreased the variac setting. I
need
to play some more but it was getting late and wanted to post this to the list
(plus my variac is still up at the cabin so Spice is all I've got for this one
at this time).

Take care,
Bart

Tesla List wrote:

> Original Poster: "Colin Dancer" <CMD-at-datcon.co.uk>
>
> Bart,
>
> Having played a bit more in SPICE, I think the parallel resistor/variac
> might well give good service for shifting the phase of a RSG.  Not having
> any capacitors seems to give a much more stable solution than any LC
> combination I've played with, and you've got fair control over the degree of
> phase shift the system can generate.  The best results seem to be when the
> resistor has a value equal to the AC impedance of the motor, and the variac
> can go from 0 to 3-4 times the inductance of the motor.  This combination
> can give up to about a 45 degree shift, though the higher the shift the
> lower the motor current.
>
> I'm currently in the process of converting a motor to sync operation and
> will let you know if the theory pans out in practise.
>
> Colin.