Re: Pig Terminology (fwd)

---------- Forwarded message ----------
Date: Mon, 27 Apr 1998 10:07:15 -0700
From: Eric Davidson <edavidson-at-icva.gov>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Pig Terminology (fwd)


The 14400/24940Y notation is the primary voltage of the transformer. 
The important number is the 14400.  There are basically 2 ways to
connect 3 phase transformers or 3 single phase transformers, the Y (or
star) and the delta connection. There are other connections used to
obtain 3 phase transformation with 2 transformers, the most popular
being the open delta connection. In the delta connection, each
transformer is connected phase to phase, and this voltage appears across
each transformer. In the Y connection, one end of each transformer
primary is connected together (the center of the Y) and the other ends
are connected to the lines. The center of the Y is usually connected to
a grounded neutral conductor for a number of stability and safety
reasons. The voltages in a 3 phase system are obviously 120 degrees
apart and they add vectorally.  If you put a voltage E across any two
legs of the Y, the voltage from the end of the leg to the center (i.e.
across the primary of a Y connected transformer) the voltage will be
E/1.732 (sqrt 3). This is where the 14400/24940Y comes from:
24940/1.732=14400.  This transformer (and 2 others) could be used in a Y
connection, across a 24940 volt, 3 phase line. The number you care about
is the 14400 or single phase primary voltage. If you put 240 volts
across the secondary, 14400 volts will appear on the primary (HV) side. 
Now you know where voltages like 208 and 277 come from! Im not sure what
to tell you about the taps, usually they are listed as A,B,C etc, but in
any event, any taps the transformer has will be defined on the tag.  You
really don't need to know about the taps before you buy it. The + or -
could apply to polarity (most transformers have subtractive polarity),
again, not important for Tesla use. I would make sure you get a 2
bushing primary (HV), its more versatile, IMO. Yes, the 3 kVA unit could
be run at 6 kVA with a reduced duty cycle.  I have a 5 kVA unit and it
weighs about 200 lbs. I built a 2 wheeled cart for it. Its not easy to
move without a cart. I didn't mean to be so long winded. If you have
more questions email me direct if you want.  Hope this helps!

Eric Davidson

> Question:
> I have a description of a couple of pigs that are available, but I am
> confused, and would like to get a translation from those that are
> more familiar with the beast:
> Primary is listed as 14400/24940Y, there is an impeadance listed,
> and for taps, there are (+, -, N, J) listed.
> I am trying to translate this notation.
> Specifically: what is the 24940Y?
>               What are the various tap listing mean?
>                  I assume - is none, but perhaps that is what N is?
> Also, the possibility exists to pick up a 3KVA unit, in place of
> the 5KVA.
> I am assuming the smaller unit would be easier to move about,
> but I want to make sure I can push it as hard as I  think I can.
> the 3KVA unit could be run at as high as 6KVA, yes?
> [Or should I just bite the bullet, and live with the larger
> size of the 5KVA unit?]
> I know, always go for more power, but I need to make it fit in the garage
> too :)
> Thanks.
> --
> Michael Baumann  Optivus Technology Inc.|Loma Linda University Medical Center
> San Bernardino, California. (909)799-8308 |Internet: baumann-at-llumc.edu