Re: HV xray cable revisited

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Conner <steve@xxxxxxxxxxxx>


> The advantage I see is if a secondary arc makes it to the cable, the 
> current will be returned to the base directly and not thru the mains ground.

Here's something to ponder: Does the current from a strike really 
want to return to the base of the coil? The coil is an inductor so it 
will have a very high impedance to the high frequency strike current.

I think the strike current (or at least the highest frequency 
components of it that cause flashovers, EMI etc- it's hard to deny 
that the fundamental frequency returns to the coil base) actually 
comes from the topload capacitance, and hence it wants to return to 
the other "plate" of the capacitor. That would be the surrounding 
walls and floor (and any wiring in them and any metal objects nearby) 
To my mind this is a very powerful argument for using a large 
counterpoise if not a full Faraday cage, when you play with arcs to 
ground in the vicinity of any sensitive equipment.

You might wonder what higher frequency components I'm talking about? 
A ground strike discharges the topload capacitance very suddenly- in 
a matter of nanoseconds- and this transient contains a whole band of 
high frequencies up into the 10s of MHz. It's basically a Hertz type 
spark transmitter.

Steve Conner
http://www.scopeboy.com/