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Re: HV xray cable revisited



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/