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Re: Pig Question
Dan,
Single bushing 7620/240/120 transformers are used in single phase and Y
connected 3 phase banks in a 13,200 volt system. It is very possible to
connect two transformers in series to yield 15,240 volts. If you look at a
Y connected bank, two transformers are connected "in series" from phase to
phase, with the "midpoint" connected to a grounded neutral conductor. Since
the voltages are 120 degrees out of phase, the voltage between phases is
7620 * (sqrt_3)=13,200 volts. Connecting these two transformers in series
and powering them from a single phase line will work fine. Be very sure to
check the polarity of each unit (additive or subtractive) and connect them
accordingly! Correct phasing will have to be done on the LV side
(obviously). Be sure to ground the mid point (the tank, on single bushing
units) especially if their impedances are much different. BTW, you will get
the full amperage with the units in series! Hope this helps. Be safe!
Eric
edavidson-at-icva.gov
> 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).
>
> 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
> keep the wattage the same. I would want to reduce the amperage so i don't
> have nightmarish spark gap quench problems.
>
> Also when wiring the these transformers in series, do you just connect the
> ground (the case) together and draw the HV off each bushing?
>
> And what is the 'up-to-date' current limiting method? arc welders and
> resistive ballast (oven elements)?
>
> thanks
>
> Dan