Terry's NST protection filter.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <yevaud_new.uk-at-excite.co.uk>


Hi -

Firstly thanks to all who replied about a source of Al duct in the UK...I
tracked some down at the weekend and now have a gleaming new toroid :-)

I'm planning to use Terry's NST filter as it appears in his NSTFilt.jpg with
my 10kV 100mA 50Hz NST. Thought I'd better check, first of all, if I need to
make any changes to the component values ?

One thing that did occur to me.....matching the transformer impedence to
that of the capacitor at 5O Hz gives a value of about 0.032microF. With the
filter in place does it change the situation at all.....that is, does the
filter drastically affect the impedence across the terminals that the
primary capacitor "sees"......or, the other way around, the impedence of the
filter and tank circuit that the transformer "sees" ....and so is this
impedence matching process to find the right capacitor altered significantly
?

One last thing....if there's a spike formed in the tank circuit then
presumably the RC filter works by the impedence of the capacitor being very
very small compared to the resistor so that all the p.d. is across the
resistor and it dissipates all the energy associated with the spike
harmlessly as heat ? Or, put another way, that the capacitor looks like a
direct connection to earth which a current spike then follows rather than
going through the transformer windings.
I was trying to sort out, then, what R & C values would have to be used and
got puzzled because I couldn't get the kind of values that Terry uses. Is
there a webpage somewhere that explains Terry's choices ?

With thanks,

Alan.





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