Re: insulation testing

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

If you want a fancier way, drive the AC output of a NST (with variac)
through a moderate resistor ( a few K), and capacitively couple to an
oscilloscope through a smallish capacitor (say, .001 uF?)... As you bring
the voltage up, you'll start to see the high frequency "hash" from the
incipient corona.

For what it's worth, this is basically how partial discharge test sets
work...  They put the excitation voltage (low voltage side) on X, and the
coupled off signal on Y, and you get an ellipse (the cap provides some phase
shift, eh?)... The position of the hash on the ellipse does provide some
information. You can also clearly see any polarity sensitivity with this
sort of test setup.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, March 31, 2002 7:21 PM
Subject: Re: insulation testing


> Original poster: "Sundog by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<sundog-at-timeship-dot-net>
>
> Hi All,
>
> For basic insulation testing, I use a NST and a full-wave rectifier.  I
> submerge the part to be tested (say a loop of enameled magnet wire) in a
SW
> bath and put the negative lead of the FWR in the bath, and the positive to
> the item to be tested.  Then I bring up the voltage with a variac and
watch
> the amp-clamp on the NST primary.  When the current spikes, that usually
> means it's broken through the insulation.  This is a pretty basic and
crude
> test, but it works for me.
>
> Shad G2-1203
>
>    At 12:11 PM 3/30/02 -0700, you wrote:
> >Original poster: "PotLuck by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> ><potluck-at-xmission-dot-com>
> >
> >Hi List,
> >Has anyone done home insulation testing? I'm primarily interested in
whether a
> >material will "hold off" a certain voltage or not. I see on the net in
> >commercial testing such tests for power factor tests, power losses and
> >monitoring of currents in the uA area. These of course are important
> >properties
> >of a material but may be a little too in-depth for home testing and the
> >properties I'm looking for.
> >
> >The voltages I'm interested in looking at are in the range of ~7.5Kv at
60Hz,
> >not in the RF range inherent in normal tesla coil operations.
> >
> >Any suggestions as to an "apparatus" that can be made easily? I have
various
> >NSTs, variacs and transformer oil at hand along with a scope and several
> >multimeters.
> >
> >Simply using a two electrodes with the material in question placed
between
> >them
> >(not under oil) sometimes produced a purple haze or what appears to be a
> >corona. Allowing the test to run for several minutes with the corona
didn't
> >appear to form any holes in the material, not by the naked eye anyway,
and
> >there was no burning. I've looked at mylar, polypropylene and HDPE.
> >
> >Mylar film (adhesive backed) from McMaster-Carr has a dielectric strength
> >rated
> >at 7500 V/mil. with 4mils placed between the electrodes "corona"
developed at
> >about 4000 volts but no damage to the mylar was apparent. Again this was
not
> >under oil.
> >
> >But what is it I'm looking for? Lack of corona? Corona can't be good.
> >
> >I'm relatively new to the high voltage arena so and advice in this area
would
> >be greatly appreciated since insulation is a big part of coiling.
> >
> >Thanks in advance! :)
> >
> >Rick W.
> >SLC
>
>
>