Re: srsg + mots - happy couple?

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


> Original poster: Steve Conner <steve@xxxxxxxxxxxx>

> But I have heard other stories of people frying series strings of
> MOTs.

for example, having connected 6 of them without any oil? it`s easy :-D

> I measured the DC resistance of
> both windings, then measured the leakage inductance by
> shorting the secondary, driving the primary with a low
> AC voltage, and measuring how much current it drew.
> Z=V/I and then Xl=sqrt(Z^2-R^2). Where R=
> Rpri+(Rsec/turns ratio^2) This doesn't take saturation
> into account though.

there can`t be any saturation, coz you are "driving the primary with a
low AC voltage" - isn`t it?
but  doing this you must measure the resistance of the windings very
precisely, and the primary  resistance is very small...
anyway - in the mot case XLs would be 5 times more than R, so there
will  be no problem i guess. in my method we must take into account
the saturation, so i`ve done 4  measurings - from 60 till 135v - all 4
results were approximately the same.

> The shunts look identical to a ballast inductor, that
> is an inductor in series with either the primary or
> the secondary. The parameter that they influence is
> the leakage inductance as I measured above. (or K,
> it's the same thing) They do store energy.

ok - i was wrong - of course they must store the energy - like any
other object that contains  concentrated magnetic field. but this is a
very non-linear inductance - for example the shunts  could saturate
and then it`ll begin to fall, so - maybe it`d be better to remove them
and wind a proper air gapped (read - linear) inductor? :-)

> I think what mostly kills transformers and ballasts is
> primary strikes. You get a huge spike of voltage that
> tries to fight its way back through the power supply
> to ground.

i`m thinking so too, by the way because of the high du/dt most likely
we can`t practically do anything with it :-(
so - no (flat) primary - much less problem, again %-)

> Safety gaps between the HV terminals and
> ground might help that.

unfortunately according to B & R at fast rise times the electric
strength of the air gaps may be  several times higher than at LF, so
it seems it`s impossible to make a gap, that helps in such case :-(