Re: [TCML] Pole Pig Question

["David Rieben" <drieben@xxxxxxxxxxx>]

Hi Miles,


Although this probably has been discussed in the archives, that's a mighty
big repository to have to draw from without some type of glossary to as-
sist in "narrowing it down", so I'll address your question(s). ;^)

First of all, for handling pole transformers, a personal forklift is not 
neces-
sary, although it sure would be nice! :^)) Many of us invest in an engine
hoist (cherry-picker) - Harbor Freight, Northern Tool, or even Autozone -
for moving around multi-hundred pound loads, like pole piggies. You can
likely find what you need at one of these outfits for $150 - $200.

As far as rating, a 10 kVA rated unit should be able to handle just about
ANYTHING that you could throw at it from measely single phase resi-
dentail service ;^| as pole transformers are VERY CONSERVATIVELY
rated. You could go with a 15 or even a 25 kVA unit if you were so in-
clined but really, anything above a 10 or 15 kVA rating , at the most, is
really going to be overkill. And, two reasonably strong men can in fact
"manhandle" most 10 or 15 kVA units, if an engine hoist or 2-wheel
dolly is not immediately available.

As far as the voltage rating, 14,400 volts is a pretty common primary
distribution voltage among the electrical utilities and is also a good ball-
park voltage for the primary circuit of a large, SG fired Tesla coil. With
the significantly lower primary voltages (secondary for coilers), it becomes
increasingly difficult to design a rotary spark gap that will allow for 
reliable
switching and quenching without risk of electrode collision. Also, the 
energy
of the capacitor discharge increases with the square of the supply voltage,
so a 14.4 kV transformer could charge a given primary cap with 4x more
energy than a 7.2 kV transformer, assuming, of course, that the cap's
voltage standoff could take the higher voltage. OTOH, at voltages much
above 20 kV, then you start running into corona problems that offset the
energy gain advantage. So long story short, I'd be looking to try to score
a 10 kVA rated polemount distribution transformer, with a voltage rating
of 14,400/24,940Y volts primary - 120/240 volts secondary. In single
phase usage, you simply ignore the "Y" rating voltage (24,940Y).

I'd presonally stay away from potnetial transformers (PTs), as they are
relatively small and you will probably find that you'll want to go bigger.
(that's what usually happens to a die-hard coiler) ;6))

I guess you do realize that pole transformers are NOT internally current
limited like NSTs, OBITs, or, to a limited extent, MOTs.? Stepping up
to these big boys will require external ballasting and many SG coilers
opt for a 240 volt input arc welder to act as a ready made ballast. Simply
hook the 240 volt input to the pig in series with the 240 volt input to the
stick welder, short the welding output electrodes together, and turn up
the amperage selector to what ever you desire. I've found when I was
using the Lincoln 225 amp arc welder in one of my previous projects
that turning up the amperage selector to 225 amps would allow my
big coil to draw 45 to 50 amps from the 240 volt service.

Hope this helps,
David Rieben



----- Original Message ----- 
From: "Miles Mauldin" <teslamiles@xxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Friday, March 05, 2010 8:06 AM
Subject: [TCML] Pole Pig Question


What size is optium? 10kVA, 50, 75? 12.5kV or 14.4kV? Seems to be a very 
large difference in physical size and weight; I am seeing 10kVA at 32" 
height and 280lbs up to 75kVA at 58" height and 675lbs. Do you just man 
handle these around, or you guys have personal forklifts? I eventually want 
to use a pig but didn't realize I'd have to become a weight lifter.

Should I really be looking at Potential Transformers instead? Or Plate 
Transformers?

Thanks,
Miles
PS If this is in the archives somewhere feel free to point me there.
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