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Re: SG questions cont'd + power factor

At 09:40 AM 01/05/2000 -0500, you wrote:
>In a message dated 1/5/00 6:22:08 AM Central Standard Time, tesla-at-pupman-dot-com 
>writes:
>
><< If you energize the core with 60mA of DC current and then suddenly remove
> the current source and switch a resistor (the resistor could have always
> been in the circuit if it is taken into account) across the windings.  Then
> you can watch the voltage decay through the resistance and calculate the
> inductance.  Since the resistance of the secondary is rather high, you
> would probably need around a 300 volt power supply to do this.  However, I
> "think" it would give the answer we are looking for here...
> 
> Does this approach sound reasonable or is there some other way to measure
> this??  Any shunted transformer experts out there??
>  >>
>
>Terry and all,
>
>Thank you. It is begining to penetrate that we do not know the secondary 
>inductance of a NST and
>so long as we don't saturate the core, we really don't care what it is. The 
>DC resistance of a 15/30  I will try the L / R measurement and get back to 
>you probably by Monday. Can you please respond to the
>LTR question: Does an LTR system mean higher than 60 Hz? If Fres is 60 Hz 
>using a
>0.025 uF cap, XL is
>120,000 Ohms and L = 312 H and all is well. Please tell me if I'm all wet! 
>I'll have plenty of towels ready. 
>
>Happy day,
>Ralph Zekelman
>

Hi Ralph,

	It will be very interesting to see what you find with the LR curve test!
I don't have a nice 300V DC supply to do it with myself.  There may be an
interesting twist to all this.  Since the B-H curve is not linear, the
inductance may not be linear either.  If you test the inductance at
different current levels you may get somewhat different answers.  This is
sort of like those ceramic capacitors that have different capacitance at
different voltage levels.  You may see that the discharge curve does not
quite follow the i = e^(-Rt/L) function due to this non-linearity of the
B-H curve of the transformer's core.  Perhaps the thing really does not
have a fixed inductance but an effective or average inductance...  Like I
say, it just keeps getting worse and worse.  However, we should be able to
get sort of close at least.

Sorry for missing your LTR question.  I have many projects going but only a
one-track mind ;-))

The big problem with LTR design is that the functions are non-linear.  The
typical sine wave functions like z=2 x pi x L start to lose accuracy rather
dramatically.  Thus, computers are used to crank through the zillions of
iterative calculations to find the answers.  You may want to check out
Richie's great site and information on this:

http://www.staff.ncl.ac.uk/r.e.burnett

LTR came up (in my case) when I was trying to find the biggest cap my 15/60
neon could charge with MicroSim last winter.  I found that I could charge a
17nF cap to 21000 volts just by using that size cap.  However, when I
started playing with the phase of the sync gap firing, I could use a still
larger cap.  After much trial and error, I found that the 15/60 could
charge a 28nF cap if the gap was set to fire 3.5mS later than the peak in
the waveform.  That sounds odd but Richie's moving animations show the
effect.  By charge a 28nF cap to 21kV and firing 120 times per second, the
system is fed 740 watts of input power or 6.2 joules per bang, which is
very high for a single-transformer 15/60 system.  The current and voltage
go a little higher than the transformer's specs but they are not dangerous
(24kV peak, 85mA RMS).  With careful PFC cap selection, I input about 8.5
amps at 120 volts or 1020 real watts.  Thus the thing is about 74%
efficient from wall to available cap power which is super good.  What was
really nice is that when I modified my coil to match the MicroSim model,
all the voltages, currents, and waveforms were just what the computer told
me they would be (the sparks were very nice too!!).  Sort of a "triumph" of
Tesla coil modeling!  The neon in that model is measured as I described in
the other post but I had to do some "tweaking" to get all the parameters to
give inputs and output that match a real transformer.  I now wonder if I
could have had a different secondary inductance and still tweaked the model
to still give good results.  It is like there are two outputs but 10 things
to adjust in the model.  So given a few parameters, I may have been able to
adjust the thing to still work no mater what the initial parameters are.
That is why I now question the inductance values in that model and wonder
if they are "real" or not.

The resonant effect of a 15/60 at 60Hz with a 10.61nF cap may be true as
Antonio and others say.  That would suggest that the secondary inductance
is 663.15H.  Since the step up ratio is 125, one would think the primary
inductance would be only 0.04244H.  However, if one drops a inductor of
that size across the AC line (open load secondary) you will draw 7.5 amps
which is clearly not the actual case....  Thus, I adjust the inductance
much higher so that the open load current draw matches a real transformer.
Now enter the shunt in the transformer (I play with coupling to add this
effect) and the non-linearity of the core plus losses and it all gets
messy.  Fortunately, the models seem to work so these effect are either not
very significant or the models are just darn good at modeling things no
mater what numbers you start with...

I guess if all else fails we could just call France and ask them, but that
would be cheating and they may tell us it is really a complicated mess
anyway...  Since the shunts seem to be a skilled "hands on" adjustment,
designing these transformers may not be at all easy and they may have to
hand adjust them because they simply can't design perfectly before building
them and seeing how they turn out.

Cheers,

	Terry