[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

> Original poster: "Drew Murray by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <drewallmighty-at-hotmail-dot-com>
> OK,
> What is the difference between a Distribution transformer and a potential
> transformer?

Hi Drew...

Potential and Distribution transformers require ballasting as where NST's
and OBIT's dont.  A NST/OBIT can
be powered directly off of the wall voltage ( these 2 types of trannies
have self limiting current
regulation to a degree). PT's and DT's have no self limiting current
regulation, if you were to connect
them to the wall voltage directly with no ballasting ( be it either
resistive of inductive..  more on this
later) it would draw as much amperage as it possibly can -  thus blowing
the circuit breaker or fuse. DT's
( pole pigs) can draw 100's of amps ( theoretically as much as the pole pig
"supplying" your house can
deliver but thanks to codes and regulations we cant do this too well unless
we wire directly from the
meter pan,  but this would be bad )

as far as the difference between PT's and DT's ...  DT's can handle 100's
of amps ( a standard 10KVA unit
can safely eat up 40 - 50 amps at 240V, in short run sessions they can
probably handle up to 80A for a few
seconds at a time) they are made to take 14400V and turn it into 240V with
a capacity of 40A continious
feed. If you have ever noticed, sometimes you might see your lites dim when
a neighbors A/C unit kicks on,
this is when the DT has almost reached its maximum continious amp rating. (
which could be near 60 - 80 A
) .

PT's are used to monitor the voltages of the Hi Volt systems. Normally they
are used to take the operating
hi volt and very precisly lower it to an exact ratio ( normally 14400 to
240V)  they dont supply much
amperage since the low end is used to power meters and such. BUT...  they
are still wonderful choices for
Tesla coils.

now for a bit of info on ballasting...   by putting a resistor in line (
parallel) with the DT or PT one
reduces the amount of current and voltage going to the transformer. Some
instances of makeshift resistors
used for this are heating elements for dryers, stove elements or hot water
heater elements. By adding
resistors the overall resistance drops thus allowing more current to flow
to the transformer BUT as you
add resistance, the voltage to the transformer also drops reducing the
overall output of the transformer.

Inductive ballasting is a second way to reduce the current going to the DT
or PT. Inductive ballasting
works by shifting the current phase of the AC signal ( this requires a book
to read about ). The good
thing about inductive ballasting is that the voltage drop is minimal
compared to resistive ballasts.

some examples of inductive ballasts are items like AC arc welding machines,
inductors ( basically a
transformer with one coil) hi amperage capacity variacs, and the saturable
core reactor.

as your note mentioned, you are being offered a PT for free   dont pass it
up take it. In this field, if
someone offers you something for free  grab it cuz sometime sooner or later
you will be able to use it.
And if you cant use it, offer it to some one who can...

Scot D