[TCML] my Pig Terry Filter

[FIFTYGUY@xxxxxxx]

Folks-
 
    FWIW I added a pic of the Terry Filter I made for  my pig, and some pics 
of my control panel:
 
_http://members.aol.com/fiftyguy/highvoltage.html_ 
(http://members.aol.com/fiftyguy/highvoltage.html) 
 
 
    The Terry Filter definitely cured one problem that  I noticed, where the 
control cabinet actually "zapped" to my knee a little  during runs. This 
seemed like a Very Bad Thing, since the cabinet is  solidly grounded to house 
ground at a receptacle directly under the main panel,  which has a typical ground 
rod nearby. Furthermore, the pig has a floating  primary and secondary - 
neither are connected internally to the case, although  I'm sure the core is. 
    I ran a wire from the star-connection point of the  RF ground under the 
coil back to the Terry Filter, which bolts to the pig case.  The MOV's are 8.4 
kV MCOV distribution arrestors. 
    Since I was pushing a lot of current with a pig, I  waned to keep the 
resistance down. So I used two 68 Ohm resistors in series in  each leg, one 
mounted on the filter itself, the other under the coil.  Consequently, I had to use 
a much higher capacitance to maintain a reasonable  cutoff frequency of the 
filter. Six caps in each leg, .036 uF 2500 V   (Vishay MMKP 383 series). Nice 
pretty blue, and yes, there are resistors mounted  under each one. 
    I've only seen the safety gap fire once while  running, just a very small 
spark when I pulled in the power contactor to the  pig. But it instantly 
extinguished, with no climbing arc. I put the gap closest  to the pig, so the 
primary tank caps would have to go through the resistors to  discharge (a little 
easier on them, and less likely to power-arc at the safety  gap). 
    I also wonder about all the fuss to avoid filter  chokes on the high 
voltage side, since wirewound resistors have non-negligible  inductance (>100uH 
each according to the manufacturer, and I measure around  70uH each on mine). 
    Everything's mounted on backboard made of a couple  sheets of 1/8" 
"fishpaper" glued together, with an angle iron support bracket  that also provides 
ground connection points. That's over $120 worth of  insulating sheet according 
to the Federal Stock Number, but surplus it's only a  buck for a 2'x4' sheet. 
Acrylic and Polycarbonate have gone through the roof -  so if I don't need to 
see through it or bend it, I'm gonna be using the  fishpaper wherever I can!
    
        The control cabinet pics  are just to show how much stuff you can 
cram in one small box!
 
-Phil LaBudde

Center for the Advanced Study of Ballistic  Improbabilities



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