Re: Pole Pig Ballast

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 
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