Re: Z-Machine Sparkage - Substation Fault

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

Original poster: "David Sharpe by way of Terry Fritz <teslalist-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

Hi Bert!

Tesla list wrote:

 > Original poster: "Bert Hickman by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>
 >
 > <<SNIP>>
 >
 > BTW, for those who've read this far, some more interesting "sparks and
 > arcs" stuff can be found at a new page on my web site. On this page you'll
 > see a picture of the world's longest manmade spark (325 feet!), a 1.2 MB
 > MPEG of a 345 kV 3-phase air break gang switch opening "hot" (it's gotta'
 > be the world's biggest Jacob's Ladder!), an awesome 5.1 MB MPEG of a
 > substation arcing, resulting in explosion and fire from a big power
 > transformer,

The substation main bus flashover and subsequent transformer conflagration
are the most spectacular and powerful demonstrations I've ever seen for the
need of over current protective equipment.  I'm going to show at an electrical
safety training class at work, just to illustrate how bad a high power fault
can be.  The 345kV switch arc over is the CORRECT response, a line side
OCB cleared the phase to phase fault, and any damage that was done was
limited to the switch contacts that flashed phase to phase..

The only condition that I'm aware of that would cause a main LV bus to
flashover and "burn baby burn!" is  inoperative OCB controls, or a main
bus in the substation with no secondary (transformer) protection between
the secondary bushings and the line side of the feeder OCB's.  Add a
snake, owl, possum, hawk, squirrel, etc. or equipment failure like a
insulator flashover or line spike on the unprotected bus, and things get
exciting fast; as on the order of 15 secs. or less in this case.  That 
transformer
was not a chump transformer either, from vantage point about 100 yds away
would guess a 20MVA or there abouts.

So the connection the Tesla Coils?  They are simply:
1.  Use over current protection on your equipment.  Very high peak spikes
      (100's of amps) is possible on larger machines, and having inadequate
      OCP is an invitation for thermal disaster.  Size the OCP for the 
load, and
      size wire for no more then 80% ampacity at full load.
2.  Over build protective circuits and systems for TC use.  I use 600V
      industrially rated (not commercial rated) components for the power
      path; not being able to successfully isolate power on an operating system
      in an emergency is not just bad form, it can be positively lethal!!!
      Ditto on fusing, I use FRN rated fuses which are rated to interrupt
      up to 100kA at 250V without rupture (and possible fire hazard).
      600V FRS rated fuses with kickback and possible HV spikes would
      be even better.
3.  Rapidly building (throwing together) to test an idea might be ok for
      a small table top coil, but is a dangerous design methodology for
      250V / high power machines.  I've seen a 20kV 2kVA PT powered
      by 2X12AWG paralleled on primary burn the insulation off of 20' of
      wire with a HV power arc, in less then 2 seconds!  Imagine what
      could happen to your home with wires hidden  in 2x4 walls, and
      inadequate OCP under similar circumstances!

Bert, any further information on the initial cause of that substation 
fault?  Great
find!

Best Regards
Dave Sharpe, TCBOR
Chesterfield, VA. USA


 > and a number of JPEGS showing what happens when a Link Belt
 > crane tangles with a 34 kV power feeder, and loses! See these at:
 > http://205.243.100.155/frames/longarc.htm
 >
 > Happy pulsing and arcing,
 >
 > -- Bert --
 > --
 > --------------------------------------------------
 > Out-of-Print Physics and Engineering Books and
 > coins shrunk by ultrastrong electromagnetic fields!
 > Stoneridge Engineering: http://www.teslamania-dot-com
 > --------------------------------------------------
 > <<SNIP>>