Re: [TCML] How necessary is a Terry Filter

[Ed Phillips <evp@xxxxxxxxxxx>]

Hi Ed,

The filter helps dampen those spikes back to the tranny. The safety gap 
will act like a static gap with a big bang as it's gap width is 
typically larger than the main gap. Never the less, there is RC 
filtering occurring and no LCR filtering occurring (which is good I 
think in this situation). The safety gap is still very important is an 
integral part of the Terry filter. But there is also high frequency 
filtering occurring in addition.

Take care,
Bart"

   I understand this [and the potential effect of LC filters without 
resistive damnping] and was just curious as to whether anyone had had 
failures with just a safety gap for protection.  I see you have and that 
it was of a Franceformer, my favorite type.  Where was the failure?  
Winding to winding or winding to case?  [I can't see that the filter 
would reduce the winding to case voltage.]  Several years ago I ran a 
number of simulations on the protection to be obtained from LC filters 
and concluded that the dangers were greater than any protection and that 
a simple RC filter was a lot safer.  Terry's addition of the MOV's was 
not an option with the parts available then but is certainly a wise 
precaution and I suspect the added capacitance of the MOV's below 
conduction is beneficial too.

Ed

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