Re: Ebay Pole Pigs

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

Original poster: David Sharpe <sccr4us-at-erols-dot-com> 

Hi Ken

Tesla list wrote:

 > Original poster: tesla-at-lists.symmetric-dot-net
 >
 > On Sun, 18 Apr 2004, Tesla list wrote:
 >
 >  > Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
 >  >
 >  >
 >  > The reason is a pole pig does not see short-circuit operation in power
 >  > distribution applications.
 >  >
 >  > In a TC circuit when the sparkgap fires the power xmfr is, for a 
short time,
 >  > in a direct short circuit.  External current limiting must be provided as
 >  > the short circuit current draw for a standard pole xmfr is 733 Amperes.
 >
 > Where does this number come from? With numerology, I can figure 733 amps
 > with a 10kVA transformer built to 5.7%IZ that's shorted out and being fed
 > 240 volts. Is this what we're talking about as "standard"?
 >
 > KEN

The Percent Z of the PDT defines how "stiff" a source is provided looking from
load to generator.  The theoretical short circuit current equation is:

Isc = Ifull load / (%Z / 100)

This obviously ignores the transmission line impedances to the primary of the
transformer ("infinite bus").  Short circuit interrupting capacities of 
protective
equipment are usually sized based on this "infinite bus" derived Isc.

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA