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Re: coax (grounding shield & AC?)

Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>
I really have to question Dr Res' explanation of his observed 125kV sparks from a 14.4 kV RMS line as being due to an 8 times multiplier from a Blumlein effect. Far more likely I feel, is stray HV from the TC itself. If the ground was faulty or of higher inductance (perhaps even a few loops might do) or simply not connected (I've done it too), then an arc from base of TC to the primary occurs and has to go somewhere. It will then jump the easiest low inductance path to ground. Depending on the setup this may be across the bushing to ground.
I must admit to having used thick coax forever on all my MOT and PT powered coils for both of the hot lines with the coax ground grounded to the MOT ground. It does terminate in a Terry filter though with resistance, MOV's and resistors though. I do like the earthed surround as an additional safety feature from ground strikes and also from passing over other cables, conductive surfaces, grass, cars etc. Persoanlly I feel this outweighs the very unlikely potential for a Blumlein multiplier which is actually quite complicated and involves more than one spark gap for any significant multiplication if I recall.
I would advise that you DO use coax for safety unless and until there is some data to suggest otherwise. A suitable test setup might involve using a loaded primary circuit without a secondary which might generate spurious HV.
I was going to make a Blumlein multiplier as one of many little projects I want to do. I would be delighted to get 125kV but I am sure I wont. 
Perhaps using water as the dielectric like these guys.
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=IEESEM002001000156000P11000001&idtype=cvips&gifs=yes

Peter


Original poster: "M G" <gt4awd@xxxxxxxxx>
Can the Blumlein effect create problems on a smaller power level. For instance my 9kv 30ma NST? I would assume that quiet large coax cable would be used on a PIG setup, and of course a PIG is capable of moving a lot more amperage. Also, does the effect only apply to coax being used in Tesla Coil conditions or generally any current passing through a coax cable? 
Thanks,
Matt G.


---------[ Received Mail Content ]----------

Subject : Re: coax (grounding shield & AC?)

Date : Fri, 04 May 2007 16:14:12 -0600

From : "Tesla list" <tesla@xxxxxxxxxx>

To : tesla@xxxxxxxxxx



Original poster: "Gerry Reynolds"!



Hi Matt,



What Dr R is getting at is the "Blumlein" effect. I have tried to

research this and believe it is a transmission line phenomenum when

improperly terminated. I dont know this definitively but believe its

possible to figure it out if someone would be willing to create the

effect. Presumably one would use a PIG and have a safety gap from

each HV bushing to ground to protect the PIG from damage. The

setting of the safety gap would be larger than usual so one would be

fairly certain that any firing was due to the effect and not to the

the voltages created by the TC. If we can find a volunteer, maybe Dr

R can help that person create the effect based on his

experience. Just an idea :-))



Gerry R.





>Original poster: "M G"

>

>"Don't run it with AC with ! the grounded shield on it."

>

>Hi, just wondering why it is not good to use the coax with grounded

>shield on for AC? I use coax for high voltage wire on my jacobs

>ladder. I did notice that if the grounding shield was left normal by

>the high voltage terminals of the NST it would pick up some of the

>electricity. A small, weak, arc on the other end of the shield would

>jump to anything conductive, such as your hand. Cutting the

>shield/coil of wire off about 1" from the terminals stopped the

>problem though. Is this the reason, or something else?

>Thanks,

>Matt G.
















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