[Prev][Next][Index][Thread]
Re: More Tuning/Debugging
Quoting Bert Hickman <bert.hickman-at-aquila-dot-com>
in a reply to Ed Sonderman:
> What voltage rating is the "primary" of your 5 KVA pig? By any
> chance, are you running 240 Volts into a 120 Volt winding to
> get 14.4 KV out of a 7.2 KV pig??
No Ed's pig has a 14,400V rated HV winding. I am running my pig
in the fashion you describe above.
> You may be saturating your pig...
There is no doubt you are correct, my pig is most definately
saturating, and I don't need to run diagnostics to know it.
> When this occurs, the output voltage will no longer be
> sinusoidal. The "tops" of the sinusoid flatten out, and you may
> not be able to charge the caps to the voltage necessary to
> break down the gaps.
This has not appeared to be a problem. The energy output would
seem to be sufficient to charge the caps up just fine. The
problems do not seem manifest themselves in the gap.
> Jim's system saturates his pig, but it seems to run OK (with
> perhaps some fairly high voltage spikes as the pig comes
> into/goes out of saturation in series with the ballast...).
Now this strikes a cord with some of the recent problems I have
been having. Let me digress back a moment first.
Having had some experience in pushing inductors into saturation
at 60 cycles I can list a practical guide. Assuming you are
simply over-voltage static testing the equipment (meaning there
is no load) things will begin to hum rather noticeably as you
push the inductor into saturation. As you continue to add voltage
the hum gets louder and things begin to actually buzz. At this
point if your inductor is small, things will begin to heat as the
unloaded inductor begins to pull real current during the static
test, a pretty clear indication of saturation.
At this point small inductors in air (read 10 amp 120 volt
variacs) begin to smoke some. Heavier inductors in oil (pigs)
don't get hot very fast, but they begin to growl rather badly.
Now I may be spinning pure BS (to use the technical term), but I
get the impression that the field flux in an inductor that is
throughly saturated during over-voltage operation is not stable.
You mention above that the possiblity of fairly high voltage
spikes could be evident as a pig goes in and out of total
saturation while placed in series with ballast. I would guess
this would be emphasized to an even greater degree if the ballast
was purely inductive.
This is the root of the problem I have been dealing with.
Resistance added to the ballast soothes things down, but the
results are still not satisfactory. To bring the "bumping" and
"spiking" under control with resistance means giving up the
14,400 volts output, the whole purpose of running with the
overvoltage in the first place.
This is perhaps compounded by the huge amount of inductance in
the system. Locally, if you start with the 50KVA pad mount
transformer that supplies my house (and a few neighbors), then
add in the arc welder, 60 amps worth of 240 volt Powerstats, and
25KVA worth of pig, we are talking about some serious inductance.
The actual delay as measured on a stop watch exceeds 1.5 seconds
from the time the welder is opened up to the time spark leaves
the discharger on a coil. We are talking real horsepower tied up
(hopefully tied up) in magnetic field flux throughout this power
supply.
Just the right amount of resistance can get things working pretty
well, but the balance is precarious at best. Any substanial
altering of the system inductance, either in the current limter
or voltage setting on the variac, throws everything out of wack.
This is rather frustrating because not only do I love smooth
systems, but I have too much invested in my power control/supply
to want things welded up into a useless mass. This would also
appear to be a handy way to lose a few line filters.
Sooo.... And I tuck this down here where few will probably really
read it... I admit defeat. The 25KVA 7200-120/240 pig is not
satisfactory when run saturated to supply 14,400 volts. A major
change is in the making and I have a question or two to pop out
for those whom I have not yet put to sleep.
1) Pros and cons on: a) plunking down $335 for a 14,400 10KVA pig
and using that for the standard lab supply; b) plunking down a
similar amount for another 7200 volt pig and running two pigs
with the HV windings in series to get the 14,400 volts needed.
2) Since I have already have an investment in the 25KVA pig which
is rewired on the low voltage side so that both 120 volt windings
are in parallel ("Star")... If I plunk for another 7200-120/240
pig, would it be better to rewire the second pig to match the
first, and run the two "Star" wired LV windings in series to get
to 240 volts input... Or, should I rewire my existing pig so that
the LV windings are back to the Delta configuration (both LV
windings in series for 240 operation) and place the LV windings
on the two pigs in parallel. Would it make any difference?
Richard Quick
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12