Re: [TCML] Pole Pig Question

[David Sharpe <sparktron01@xxxxxxxxx>]

Miles

Voltage discrepancy is based on transformer use.  These are instrument
transformers and can be
connected in three phase electrical equipment either in 'Wye" or "Delta"
configuration.  Example is
if transformer is 7200V (60:1 ratio), it would typically be connected to
one phase and neutral of a
12.47kV 3 phase service.  The transformer you are desiring has a 120:1
ratio and are "fairly" common.
A Delta connected (across two "hot legs") transformer would have two
insulated HV bushings,
I've seen wye units have one insulated bushing for phase connection and the
opposite side
strapped to the frame from the HV neutral (grounded neutral return)

Another equally good option (maybe better, double available power) is use
two (2) 7200 transformers
properly phased to create a 14,4kV: 240V transformer "bank".  These units
can be short duty (<=5minutes)
loaded to up to 250% nameplate without damage.  So 2 transformers in above
mentioned configuration
would be good for nearly 8kVA short duty.

These transformers are nearly ideal units and MUST be ballasted, the %Z of
the transformer is ~ 5%
and therefore will attempt to draw as much as 20X (!!!!!) full load current
under a secondary short circuit
condition.  I've seen double #12 per side (40A feeder) have insulation
destroyed in less then 2 seconds
when operating a 240V: 16.8kV (8400V 70:1 PT's) were operating into a
Jacobs Ladder.

Finally, these are not large NST's; these units will KILL without
provocation. They can easily supply
100's of milliamperes into a high impedance load (i.e. a careless person
providing an unintended ground
return path).  SAFETY FIRST.


On Thu, Jul 25, 2013 at 7:02 AM, Miles Mauldin <TeslaMiles@xxxxxxx> wrote:

> Hi all,
>
> I am in the market for a pole pig, and my first choice is a dual horn, HV
> 14400, LV 120/240. I se several different voltage combinations and am
> wondering what are the differences.  My biggest question is why some of the
> 7200 HV units don't list 14400 as the total HV? If this information is in
> the archives please direct to its location.
>
> 7970/13800Y
> 7200/12470Y
>
> Continue to enjoy all the expert posters and information provided.
>
> Thanks!
> Miles Mauldin
>
> Sent from a little device with a tiny keyboard.
> _______________________________________________
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>



-- 
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA

Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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