# Re: Pole Pig Ballast

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TL>>
TL>>Has anyone experienced this? Tried to run their pig with
TL>resistive >ballast only? Inductive ballast only? No
TL>ballast;) >

TL>I did try running my 5kva pole pig with no ballast -
TL>once.  It wants to draw more than 50 amps and would like
TL>to smoke my powerstat when the gaps start to fire.  The
TL>arc welder is the only means I have found that will
control
TL>the beast.  I also have three 2000 watt oven elements in
TL>parallel with the welder.

TL>Scott Myers and I have talked about building a variable
TL>inductor to replace the welder.  I believe we decided we
TL>needed a range of 5 to 25 milliheneries, wound with wire
TL>large enough to carry up to about 50 amps.

It is important to remember that these pole transformers are
originally designed to source a LV output from a HV input:
the reactance of the LV winding is intentionally low so that
the source impedance doesn't suffer voltage drops across
itself ( it is trying to look like an ideal current source
which is a short circuit). We need to add external impedance
( real or reactive ) so that when we supply 120 or 240V to
the LV winding, we see some total Z which is appropriately
high so as to match the available power supply ( i.e. 10kVA
is 240V at 40A which is what my pole transformer will see).
You could use capacitive or inductive reactance, or
resistive. We remember that the pole transformer is very
well coupled with k approaching unity, and it is thus well
regulated. This means that the impedance attached to the HV
winding is reflected back into the LV winding. When the HV
winding is short circuited ( by a spark gap, or by a C with
no stored charge) then the LV experiences the same short,
hence the need for a current limit. The advantage of using a
reactive limit is that it doesn't dissipate P compared with
a resistive limit.

Richard Craven
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CMPQwk #1.42-21 UNREGISTERED EVALUATION COPY
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