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Re: [TCML] Ground Voltage Gradient



[I maybe trending too far off topic, here.  Might be pursued off list?]

> Often Tesla coilers connect everything on the power source side
> (control cabinet etc.) to the power source ground, and
> everything on the "business" end connected to a dedicated
> RF Ground.
 
> In the case of 240V 60Hz supply (assuming a dedicated service
> with no other loads attached) both L1 and L2 would be referenced
> to ground only through the secondary windings of the distribution 
> transformer supplying the service. 
    Is this an NEC thing?  I'm thinking local grounding of entrance
    and metering is notuncommon.  May Be Rong.

> Additionally, let us assume that:
 
> The distance between the ground at the source/control point and the
> load/TC is 1000 feet (makes impedance calcs easier for the wire used
> for L1, L2)
 
> The Tesla coil uses a charging choke on the secondary of the high
> voltage transformer located at the  base of the Tesla coil
> (eliminates ballast)
 
> The Tesla coil uses a SISG (eliminates additional wiring for RSG,
> control wiring, etc.)
> 
> The Tesla coil is powered by a "pole pig" and the center
> LV bushing has been left floating because after all this is a
> Tesla coil, and we don't want that connected to RF ground. The
> case is bonded to the RF ground.

> The "pole pig" is housed inside some sort of metal cabinet, also
> bonded to RF ground (personnel safety)

> Now we know that an operating Tesla coil can produce a fairly high
> differential between RF ground and Mains ground. No question
> there. That is the point of using a separate ground, to keep high 
> voltage spikes etc. off of the mains ground.
    Seems to me the 'high differential' characterizes the differnce
    at HF 'only'?  Mains Freq differential s/b minimal?
  
> So lets say that the demonstration or display went well, everything
> is hunky dory and the coil has been disassembled and put into
> storage. For some  reason, which does not matter because this is a
> hypothetical question, the power is restored to the now unloaded
> "pole pig" all happy in its protective cabinet. Now the case of the
> pig, and its  cabinet as well, are bonded to the RF ground out in
> the field, and the center low voltage bushing is still floating, and
> should have a potential of 0V with respect to the ground at the
> source, I.E. mains ground.

> So if someone were to put a voltmeter between the pig case and the
> center LV bushing, what would it read?
   If i'm following correctly, would concur with zero(ish).  Varying,
   amongst other things, with internal details of 'piggy'
   construction, stray capacity, etc, foo, mumble.

> Are there natural ground currents that might cause a potential
> difference between two ground points separated by 1000 feet?
   Sure.  Typically measured (by all accounts: I've not done so.)
   in millivolts, except under 'special cases'.  researching
   'earth currents' and 'stray currents' will turn up some facts,
   some i regard as blather.  (I've not found much, would like a
   good reference.  Some 'research monitoring' is done.  Really
   Potent solar storms can goof up the mains system in obscure,
   off topic ways...)

> If such ground currents exist, are they constant or do they vary
> from time to time, and if so, what affects them?
   Lotsa things  8)>>

   'natural' ones, dcish, vary with solar activity, local ground
   chemistry.  Unbalanced Mains currents vary with load on system.

> What happens if a thunderstorm were to pass nearby?
    Things can get interesting....  Usually not damaging to humans,
    can bend/staple/mutilate electronics of the delicate kind.

    There have been exceptional/rare cases of faulted 'distribution'
    and 'transmission' lines that have gone Really Lethal.  Faulty
    'user gear', can, in rare cases, create hazards.
 
> TIA for any opinions, insight, etc..

best
New dwp:     dave_p@xxxxxxxxxxx
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