Re: [TCML] Pole Pig Question

[David Sharpe <sparktron01@xxxxxxxxx>]

Sorry pole pigs are connected the same as instrument transformers just
caught that!
KVA loading is till reasonable, for possibly longer period since they are
oil cooled.
They are even more dangerous then PT's, and safety precautions including a
operational
instruction and system preflight must be made, to insure your safety and
safety of
equipment.  I've been involved in OEM megawatt level transformer testing
(think
a Tesla Coil Lab built by a 35 million lottery winner), and their control
room has a
preflight procedure that is followed to the letter; to keep from nuking
(literally and figuratively)
a clients transformer, or blowing up A LOT of very specialized high power
HV lab equipment.


On Thu, Jul 25, 2013 at 8:53 AM, David Sharpe <sparktron01@xxxxxxxxx> wrote:

> 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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>> http://www.pupman.com/mailman/listinfo/tesla
>>
>
>
>
> --
> Dave Sharpe, TCBOR/HEAS
> Chesterfield, VA USA
>
> Sharpe's Axiom of Murphy's Law
> "Physics trumps opinion!"
>



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

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