Re: terry filter theory

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: otmaskin5@xxxxxxx 

Dr, another question on this.  Do the MOVs or Capacitors ever wear 
out with a lot of use to the point where they no longer do the 
job?   Or if you routinely inspect them & there is no visible damage, 
is it reasonable to assume they're still working?  Dennis Hopkinton MA


-----Original Message-----
From: tesla@xxxxxxxxxx
To: tesla@xxxxxxxxxx
Sent: Tue, 20 Mar 2007 1:25 AM
Subject: Re: terry filter theory

Original poster: "resonance" <resonance@xxxxxxxxxxxx>


The caps serve as a rapid ground source for the high freq transient 
currents due to their very low high freq reactance. The resistors 
destroy the circuit Q factor and reduce the transients. The varisters 
serve as a direct overpotential safety value to allow excessively 
high resonant potentials a direct path to ground. The safety gap 
serves as a final safety valve but these are not usually required as 
the varisters serve the same purpose ---
provide a quick, safe path to ground.

I usually split the resistors into two 500 Ohm, 50 Watt resistors, 
one on each side of the series caps to ground. From the tank circuit 
the oscillation first hits a resistor, then the series caps to ground 
(low reactance), then another 500 Ohm, 50 Watt resistor, then the 
varisters to ground, and finally a safety gap to ground. This will 
stop almost anything that could damage your nst. Be sure to use one 
of these systems off each xmfr bushing. The power reduction is so 
slight it does not adversly effect the TC output spark length.

Terry's original circuit used a 100 Watt, 1,000 Ohm resistor.

Some transformers can develop a ferro-resonance with a tank capacitor 
and this type of filter prevents this ferro-resonance while 
simultaneously destroying any reflected oscillatory currents from the 
tank circuit, e.g., the pri cap and pri inductor.

Dr. Resonance


>parts for this filter I would like to grasp the theory behind 
the >design of your filter. Do the capacitors store excess current 
that >would otherwise damage the nst? Are the movs' there to protect 
the >nst from surges? Will the 1k ohm resistors reduce the input 
voltage? >Does it take an arc at the safety gap to operate the terry 
filter in >the first place? Is it overkill to add more components? 
Will extra >components reduce the spark length?




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