Re: Potential Transformer Questions???

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Richard W. by way of Terry Fritz <teslalist-at-qwest-dot-net>" <potluck-at-xmission-dot-com>

Hi Dan,

You could use some measurements to figure something close without powering
up. Measure the center leg to get the cross-section in square inches. Call
this CS. Measure the primary and secondary wire sizes to get Circular Mils
or CM.

Get the VA rating for the core by:
VA = (CS / .16)^2

I divide the wire CMs by 1000 for continuous duty and by 750 for shorter
periods of operation, around a minute or two. This gives current carrying
capability for primary and secondary. A MOT's output is in the neighborhood
of about 2000 volts while the input is around 120 volts.

Primary current = CM/1000 (continuous) or CM/750 (peak or surge current)
Primary VA = 120 * the result found above.
Do the secondary the same way.

Whichever VA rating is lowest (core, primary, secondary) is the one I'd use
for the ballpark calculations.
After settling on a VA rating then the currents can be estimated.

The above doesn't take into consideration the shunts used in the MOT. But at
least you'll have a safe figure to start with. I think you'll find that with
most MOTs the VA for the core is lower than the VA that either the primary
or secondary can handle.

Rick W.



----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, January 13, 2003 6:35 PM
Subject: Potential Transformer Questions???


 > Original poster: "Mccauley, Daniel H by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
 >
 >
 >
 > Hello,
 >
 > I just acquired a 14400V, 120V in potential transformer which is rated at
 > 1.5kVA continuous duty.
 >
 > I plan on using this beast to replace my dual 15kV/120mA NSTs i currently
 > have on my small coil and
 > had a question on current limiting.
 >
 > I have a large ARC WELDER Lincoln (Ed Wingate type) but that is only for
my
 > pole powered stuff. And since I want to
 > make this somewhat portable, I don't want to carry around too much heavy
 > equipment.  I was planning on using just
 > a spool of 12 AWG, 500 foot wire as Terry Blake has done.
 >
 > My question is, could i safely measure the output current of my limited
 > transformer now by simply shorting the output
 > windings together in series with this spool of wire and measure the
 > secondary current via current probe to determine my output current with
the
 > ballast???  I would like to design the rest of my system around this
output
 > current.
 >
 > Or would it be better to just measure the inductance of the roll and
 > calculate the current???
 >
 > What are your thoughts?
 >
 > Also, I know a few of you have these things.  How high have you pushed
these
 > things powerwise??
 >
 > Thanks much!
 >
 > Dan
 >
 >
 >