Re: Pig setup help.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Bart Anderson <classi6-at-classictesla-dot-com> 

Hi Gerry,

Tesla list wrote:

>Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net>
>  Hi Bart,
>
>Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
>
> >>Transformer grounded to mains ground (green wire):
> >>
> >>Benefit:  transformer fault (like primary to case short or secondary to
>case
> >>short) may draw excessive current and blow breaker (note that the balast
>for
> >>a PIG or PT may not allow this to happen unless ground fault protection
> >>is used).  Case is safer, however one still has the bushings that can
>kill.
> >>
> >>Disadvantage:  A strike to the TC primary (transformer secondary) could
> >>flashover to the case and thus the mains ground and kill sensitive
> >>components (TV, stereo, etc) also plugged into the mains.
>
> > It is possible, but this is true with both configurations, including
> > floating configurations. The lowest impedance will feel the brunt of the
> > hit.
>
>I agree that the strike current will take the lowest impedance, but I think
>we need to keep in mind that the strike current is trying to return to the
>base of the TC secondary (RF ground).  If we make sure the lowest impedance
>path is to RF ground, we can be very sucessful in keeping the mains ground
>out of the picture.  With a NST, I believe any strike that gets to its HV
>bushings will arc to the core long before it finds its primary (due to
>construction).  The core is grounded to the case and if the case is grounded
>to the TC secondary base, the return path will be provided.
>
>A strike to the TC primary, when the transformer is grounded to mains ground
>and the TC secondary is grounded to a dedicated path to earth ground, will
>almost certainly make its way to mains ground (unless there is a flashover
>between TC primary and TC secondary before flashover between transformer
>secondary and transformer case occurs).

Well, I can see your point. Especially, for my particular style of running. 
I'll have to think more on this, but it makes good sense from the 
standpoint of a return path.


> > Also, consider strike rings tied to rf ground (for all those folks who
> > use them).  A probability factor comes into play by an increase
> > frequency of hits (and you will get an increase in primary directed hits
>if a
> > strike ring is used, and at times, the primary will get hit as well (espec
>ially
> > for coils with poor field control). I just prefer to minimize the
>possibility's.
>
>YES, this is a concern.  The strike rail needs to be between the TC primary
>and the topload to intercept the strike.  This of course shortens the
>distance between the topload and a target.  Field control is important and a
>raised topload (with a corona ring to protect the top turns of the
>secondary) may be necessary to not increase the frequency of primary
>directed streamers.

Yes, agree 100%! Field control is the #1 preventor of primary strikes. I 
can't ever remember the last time I had a primary strike.

Take care,
Bart


>Take care,
>Gerry R
>
> >>Transformer grounded to dedicated earth ground (aka RF ground):
> >>
> >>Benefit: a strike to TC primary that results in flashover to transformer
>will
> >>directly return to the secondary ground and not contaminate mains power.
> >>
> >>Disadvantage:  transformer fault could result in a HOT case and no blowing
> >>of the breakers if the dedicated earth ground is not adequate.  If
>adequate,
> >>the protection should be just a good as mains ground, but still no
> >>guarantees for the balasted pig or PT unless ground fault protection is
>used.
> >>
> >>I think one should define danger zones in their system design.  If the
> >>transformer is within the danger zone,  grounding to the dedicated earth
> >>ground is OK.  If outside the danger zone, the transformer should be
> >>grounded to mains ground and the bushings protected from accidental
> >>contact.
> >>
> >>One persons opinion,
> >>Gerry R
>
>
>
>