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Re: PFC Question

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Dmitry,

It has often been said that the inductance of the variac (that changes with setting) causes the phase of the charging waveform to change with setting. I have personally experienced this phase change with variac setting and assume that it is due to the variac inductance vs setting. What is needed here is to measure the phase of the variac output wrt the phase of the input of the variac to put things into perspective. Your estimate of 1mh of leakage inductance is based on a coupling of 0.99. This coupling seems high to me. If the coupling is say 0.95, the leakage inductance may be significant enough to cause the output phase shift. I have disassembled a variac of old design and found the the area of actual core to be much less than the area of the winding. It would not surprise me to find the coupling to be less than 0.99.

Another theory that may explain the phase shift vs variac setting is the non linarity of the NST (my experience is with NST's). As the variac output is increased, the NST may be going into saturation that may effectively decrease the current limiting inductance. This could also cause a phase shift in the charging waveform as the variac output is changed.

Dont know the actual truth, but there is a phase dependency of charging waveform phase vs the variac setting. This dependency requires the SRSG to be re-adjusted as the variac output is increased.

Gerry R.

Original poster: "Dmitry (father dest)" <dest@xxxxxxxxxxx>


> Original poster: Steve Conner <steve@xxxxxxxxxxxx>

> I was also surprised to read that. Say you want to
> draw 30A at 240V, the ballast reactance is going to be
> on the order of 5 ohms which is 26mH in a 60Hz system.
> 1mH is negligible compared to that.

any comments on this, Jerry?

> But, imagine you're using an ungapped variac as the
> ballast.

i can`t imagine _i_ do that - it`s just too st##id for me :-D

-----
Neon transformers are doomed in Tesla service! I should know, I've
killed more of 'em than many pople have ever even seen in a life time.
25-03-96 (c) Richard Hull, TCBOR