Re: [TCML] Strike rings - to use or not to use; was: Newbie Grounding Question

[Yurtle Turtle <yurtle_t@xxxxxxxxx>]

Just theorizing here...

Your lightning arrestor is purely voltage driven,
without regard to energy. However, a big coil like
yours could have a theoretical instantaneous output
power in the hundreds of kW. While it may not be
enough to hurt your transformer or cap, the
instantaneous event (or series of events) may have had
enough energy to fry your arrestor. It probably did
what it was supposed to, once it saw >18 kV. Once the
arrestor clamped to ground, all those hundreds of kW's
saw a very low impedance path to ground.

My arrestor consists of a series air gap, followed by
MOV's. As I understand it, MOVs can only take a
certain number of overvoltage events before they
finally fail short. My arrestor was very old, and may
have already seen some real world lightning events
before I got it. Was yours used as well? Mine's seen a
number of primary strikes without failing. However,
I'm currently only running at around 6-7 kVA.

Adam

--- David Rieben <drieben@xxxxxxxxxxx> wrote:

> Hi Gary,
> 
> I do understand what you're saying about the
> conservation of energy not
> allowing the primary capacitor to be "overvolted" by
> a streamer striking
> the primary coil during operation. And that would
> lend credence to Bart
> Anderson's practrice of not using a strike ring at
> all. However, I have ex-
> perienced running my big Green Monster coil on a
> windy day where the
> wind actually "blew" the output streamers back into
> the side of the lower
> third of the secondary coil. Although my primary
> capacitor and transfor-
> mer (pole pig) did survive the hit, my 18 kv rated
> distribution arrester
> failed as a short circuit. This didn't really make
> sense to me either as the
> base of the secondary coil as well as the primary
> coil is tied securely to
> the RF ground. And yes I WAS using a grounded strike
> ring in this case,
> so the strike ring didn't do me any good. The
> streamer completely by-
> passed the strike ring and crashed into the lower
> third of the secondary
> coil, thanks to the influence of the wind. Of course
> what you're saying 
> makes
> perfect sense, too. There simply should not be
> enough available energy in 
> the
> output streamers to be able to charge the primary
> capacitor above the 
> voltage
> that it initially discharged into the primary coil.
> It's akin to trying to 
> overvolt
> a 10 kV, 100 uFd energy discharge cap by charging it
> with a few cycles
> from a 50 kV, 5 mA flyback driver. Although there's
> 50 kV potential
> available, at only 5 mA of current, that means that
> there is only 250
> joules per second available to charge the capacitor:
> 50,000(.005) = 250
> That means that you would have to charge a 10 kV,
> 100 uFd (5 kJ)
> for a minimum of 20 seconds contiunously with the
> flyback driver
> before you'd be in any danger of overvolting the
> said capacitor.
> Still, the momentary streamer hit to my secondary
> did cause an overvoltage
> that did leave its mark - on my distribution
> arrester. Maybe others can add
> their commnets to this subject as well.
> 
> David Rieben
> 



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