Re: Anyone use MMC's with their pole transformers???????????

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Original poster: "Christopher Boden by way of Terry Fritz <twftesla-at-qwest-dot-net>" <chrisboden-at-hotmail-dot-com>

PT's are Potential Transformers (a rather redundant name if you think about 
it), and are used in things like substations, etc to lower a really high 
voltage down to something the meter can handle. They're mainly used for 
instrumentation and such. Most of the ones I come across are useless for 
coiling. I see a lot of 2,400V/120V-1.5kVA ones, the biggest I've ever seen 
personally is 14.4kV/240V-10kVA and it's sitting in a rack in our lab :) 
It's interesting because it's dry (meaning it's not in a can filled with 
oil) and is just a "Core and Coil".

XRTs are X-Ray Transformers. These vary from little ones for dental X-ray 
units up to gigantic 1600Lbs ones for lab use. They're not just transformers 
though. The ones I have seen ae basicly a oil-filled box with a *VERY* high 
voltage transformer (Usually 50 to 150kV output with a 240V in), plus a 
large rectifier setup, and another small transformer floating at HV. The 
little transformer will have something like a 5 volt difference so that the 
outputs of the whole thing will be something like 150,000V and 150,005 V. 
XRTs are easy to get, but basicly useless for coiling because of the 
exceedingly high voltages and low power levels. XRTs are designed to only be 
turned on for a second or so, whereas NSTs are designed to be run for 
decades :) If you do ever stumble across one here's a few things to know.

1. Check to see if it's rectifier is solid-state or tube. As a rule, if it's 
got a glass window on top, it's tube, often they will have either a window 
or an access panel of some sort to make changing the tubes easier. The tubes 
usually come in pairs and they're *really* big, like 3"dia (ribbed) and 6" 
long. The ones I have usually have 2 terminals on the bottom and one on top 
of the tube.

2. If it's an option, get a GE brand transformer. While I *detest* GE as a 
corporation, they have done one good thing. NO GE MEDICAL TRANSFORMER HAS 
EVER LEFT THE FACTORY WITH PCB OIL! I've heard this from several places and 
have never heard otherwise. Now, weather or not someone has changed the oil 
in the tranny with PCB is another matter, but, when it left, it was safe.

3. GET THE CABLES! XRTs often come from the wild with their cables attached. 
GET THEM! Because there worth their weight to a serious HV guy :) Those 
cables are rated to at LEAST 50kV! And the "Federal" connectors on the ends 
cost a small fortune to buy, and you'll HAVE to have them for your tranny. 
When you see the plugs you'll understand, they're about 6" long and an inch 
thick. Remember to pour a little (very little, like a shot, or it'll spurt!) 
oil into each socket before you turn it on! Keep the cables plugged into the 
HV terminals when not in use, if you get dust in there it WILL carbon-track 
and arc to the frame and they're a serious bitch to clean.

Guess how I know this? :)

If you ever have to open one be prepared for a BIG mess. The tool of choice 
is a Genie-Lift or a forklift or something similar. The whole transformer is 
mounted to the lid of the box. If you get one with lifting eyes those are 
usually the mounting bolts of the internal cage. There will be a hundred 
little bolts around the edge (oiltight *snicker* seal) that have to come 
out. Then lift from the eyes and voila, you'll have a cage with a 
transformer on the bottom, and other goodies on top.

Remember that XRTs are center tapped, like an NST. Even though you're 
getting 150kV out, it's actually +75 and -75 at any given moment, and in 
their stock configuration they're outputting DC, not AC!

Also note that, like MOTs and Pigs, PTs and XRTs are unballasted, and 
require some throttleing or you'll eat breakers :)


Christopher "Duck" Boden Geek#1
President / C.E.O. / Alpha Geek
The Geek Group
www.thegeekgroup-dot-org
Because the Geek shall inherit the Earth!

"He had that rare weird electricity about him--that
extremely wild and heavy presence that you only see in
a person who has abandoned all hope of ever behaving
normally." --Hunter S. Thompson