Re: [TCML] Terry Filter for a pig?

[FIFTYGUY@xxxxxxx]

In a message dated 9/2/08 4:13:09 P.M. Eastern Daylight Time,  
Gary.Lau@xxxxxx writes:

>Terry filters are usually used for NST's with mid-point grounded  secondary 
coils, and this is why >there are basically two of everything -  one filter 
for each side.  But with a pole pig, wouldn't you tie  
>one of the HV bushings to RF ground?  I'm not sure why there  needs to be 
two complete filters (as 
>shown in the photo link) as with  NST's.


    Sure, I could ground one bushing of my pig. But to  where? RF ground? 
Fine, I wouldn't have to worry so much about transients  at *that* end of the HV 
winding - but the transients at the *other* bushing  might be twice as bad, 
and then added to the extra 8kV over  ground that bushing would now be at! FWIW, 
my pig is Y/Delta rated.
    And as far as the complexity or number of  components - well, I'd still 
need *one* arrestor at full voltage, instead of two  at half voltage. I'd need 
a different cap configuration, but  essentially twice the series voltage 
rating at the same capacitance to keep  the same cutoff frequency. So the cap 
portion would end up more expensive.  The resistors would have to handle twice as 
much current, thus quadrupling their  power dissipation (wasted energy). I've 
got power resistors of all  sizes coming out of my ears, so for me that's not a 
cost issue.
    And overall the current  configuration keeps the filter compartmentalized 
and modular for damage  control if something goes wrong. 
    Nope, I think I like my nice symmetrical setup,  just the way Terry would 
have liked it. :)
 
-Phil LaBudde    

Center for the Advanced Study of Ballistic  Improbabilities



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