Re: Pig Question

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 8/1/00 9:20:09 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original poster: "Dan Kunkel" <dankunkel-at-hotmail-dot-com> 
>  
>  Coilers,
>  
>  I went to the power company today to see if I could procure for myself a 
>  pole pig. The company only runs 7,620 volt lines and there 10 kva-ish 
>  transformers are all single bushing. I was wondering if anyone esle has 
had 
>  experience with these kind of transformers. They are upgrading their load 
>  capabilities are getting rid of the smaller trannies at scrap cost 
>  (awesome).

Dan,

Many folks use 7620 volts for their TC's, but a higher voltage is
prefered.
>  
>  I was wondering if it is possible/nessecary to buy two trannies and wire 
>  them in series to produce 15,240 volts in order to reduce amperage and 
still 

Yes, they can be hooked in series, and that's a good idea.
> 
>  keep the wattage the same. I would want to reduce the amperage so i don't 
>  have nightmarish spark gap quench problems.

The quenching won't necessarily be nightmarish at 7600 volts I don't think.
>  
>  Also when wiring the these transformers in series, do you just connect the 
>  ground (the case) together and draw the HV off each bushing?

Yes, this is the best way to do it.
>  
>  And what is the 'up-to-date' current limiting method? arc welders and 
>  resistive ballast (oven elements)?

Resistive ballasts are not efficient, but can be used in conjunction
with inductive ballasts if needed.  (Some folks have reported that
they needed some resistive ballast to smooth out the operation.)

Some folks use large variacs with a slot cut into the core.  Other
folks use large variacs without the slot.  Others use welders with
good results.  I have not had good results using a variac as a
ballast.  I use a homemade ballast which is about 300 turns of
#12 pvc insulated solid wire wound on a 3" by 18" pvc pipe and
filled with transformer "I's" from junked NST's.  There are a bunch
of taps on the ballast which connect to a rotary selector switch
to select the desired inductance.  It works very well.

Cheers,
John Freau
>  
>  thanks
>  
>  Dan