Re: High Freqency Voltage Stress on NSTs

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

Original poster: "D&M's High Voltage by way of Terry Fritz <twftesla-at-qwest-dot-net>" <DMsHV.DavMcKin-at-verizon-dot-net>

Terry,

What type of waveform were you using for these experiments?  A pure sinusoid
would provide an equal distribution across the windings.  The concentration
in
the outer windings becomes apparent only with a steep wavefront (like the
lightning impulse 1.2 / 50 uS or the switching impulse 50 / 250 uS).  It's
like
when you take a jump rope, connect one end to a solid object (low voltage
end to ground), and then whip the other end of the rope (HV side).  You will
obtain a traveling wave down the rope.  This is similar to what happens in
the
transformer - the slang term for it is "whip up".

There are basically two theories that account for failures due to
overvoltage in
 transformers.  One of these is due to the phenomenon mentioned above -
assuming
the transformer isn't designed to handled these types of waveforms (like
NSTs).
This is one of the main reasons that there are very few failures of pole
pigs in TC
usage - they are designed to handle large impulse waveforms (both lightning
strikes,
and switching wavefronts).  The other failure occurs when an inductive
system is
capacitively loaded (such as a power factor corrected system) is being
opened.  This
occurs when the inductive arc is extinguished when a circuit breaker or
contactor is
being opened.  The arc formed (from the inductance of the system)
extinguishes, and
then the voltage jumps the newly opened gap (reignition).  If a reignition
of the gap
occurs after the initial arc is suppressed (quenched), a voltage build up of
approx. 3 times (for single phase systems), and 6.6 times for (3 phase
systems) the
operating system voltage due to resonance of the inductance and capacitance
in the system.

There is a really good book that explains these phenomena in great detail:

Electrical Transients in Power Systems, 2nd ed. - Alan Greenwood - Wiley
Interscience.  $160 from http://www.Amazon-dot-com.

David L. McKinnon
D&M's High Voltage



> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> Hi All,
>
> I tested an NST for high frequency winding stress.  The data is at:
>
>
http://hot-streamer-dot-com/TeslaCoils/MyPapers/NSTWindingStress/NSTWindingStres
> s.html
>
> That is supposed to be one line.
>
> It is also the first paper at:
>
> http://hot-streamer-dot-com/TeslaCoils/MyPapers/MyPapers.htm
>
> Perhaps we need to rethink the use of NST filters...
>
> Many thanks to Billy for the NST too!!
>
> Cheers,
>
> Terry
>
>
>