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Re: 50 KVA Pole Pig


Jason,

Those pigs will not be any harder to ballast than their smaller cousins.
Even very small distribution transformers do not have nearly enough
internal impedance to adequately limit current, so essentially all of
the ballasting has to be supplied externally.  With a suitable choice
of ballast you can use one of these to run a tiny coil drawing less than
100 Watts.  Of course, with a different ballast a much larger coil
could be operated.

If you only plan on using one (if the two higher-voltage transformers
have taps and you have access to 3-phase power you could build a rather
large DC power supply with all three), maybe you could give your location
in case others have use for the remaining two.

Something you may want to look into with such a large transformer is
the ability of your circuit breakers or fuses to open if it is
accidentally shorted.  This will be determined based on the percent
impedance of the transformers, the impedance of the wires leading to
the transformer, and the interrupt rating of the breaker/fuse.

As I understand these ratings (and if there are any errors, someone
please correct me) here is an example assuming a typical percent
impedance of 1.5%:

  50 kVA / 240V = 208.3 Amps at full load
  208.3 Amps / 0.015 = 13,889 Amp drawn by the transformer when the LV
    side is connected to an ideal voltage source and the HV side is
    shorted.

Typical circuit breakers for residential use are rated to interrupt
up to 10,000 Amps, and fuses up to 20,000 Amps.  So if the wire
supplying the transformer is heavy enough, you may have some problems
if you are using circuit breakers.

Jim Monte


>Date: Tue, 04 May 1999 04:15:22 -0600
>To: tesla-at-pupman-dot-com
>Subject: 50 KVA Pole Pig
>From: Tesla List <tesla-at-pupman-dot-com>
>
>Original Poster: Jason Zuberer <jason-at-vortexia-dot-com>
>
>    I recently came upon a total of three 50 KVA, RTE (brand?) pole pigs
>that I can have for free. They all work and are certified NON-PCB and
>weigh in at 790lbs each. The question is how easy would it be to limit a
>pig that large and what monster of a coil would I need to build to
>utilize it?
>    I have access to 2 pulse rated caps at .05uF-at-50KV and can build a
>rotary gap if needed. I have a feeling that the pigs are overkill, but
>who can resist free!
>
>    Pig specs:
>                    RTE# 14400/24940GRDY -120/240 50KVA NON-PCB
>                    RTE# 13900/23900GRDY -120/240 50 KVA NON-PCB
>                    RTE# 14400/24940GRDY -120/240 50KVA NON-PCB
>
>Please give advise soon, I have to pick them up this week if I want
>them.
>
>                Thanks
>
>                            Jason Zuberer
>
>