Re: [TCML] Toroid question

["Dex Dexter" <dexterlabs@xxxxxxxxxxx>]

Bart,
I agree with Jim on this one.It's true I am new to the coiling but NOT so new to the ordinary iron core transformers.I have no idea how much above designed rating we can push NSTs.However, I can tell what can happen when 30 MVA, 3 phase transformer is overvolted by 73% per leg (phase voltage vs. line voltage rise fault).Explosive death of it in  a second!Not even HV circuit breakers couldn't prevent the disaster.Careful with overvolting.

Dex 
     

--- jimlux@xxxxxxxxxxxxx wrote:

From: jimlux <jimlux@xxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Cc:
Subject: Re: [TCML] Toroid question
Date: Sat, 06 Jun 2009 08:13:49 -0700

bartb wrote:
> Hi Gary,
> 
> That is an interesting point indeed.. But I'm not so certain the claim 
> you stated is certain. For example, I tested 0V to 150V on a 15/30 NST 
> for various measurements. In this example, take a look at Vout, when Vin 
> is pushed beyond the 120V measurement.
> http://www.classictesla.com/temp/15-30nst-vout-vin.gif
> Note that Vout begins to diminish linearly to the previous input values 
> linearity. Also note this is open circuit Vout (nothing terrible 
> occurred, but not a recommended measurement).
> 
> Here is a look at short circuit current through 120V up to 150V. EXTREME 
> LINEARITY! This is telling.
> http://www.classictesla.com/temp/15-30-shortcircuitcurrent.gif
> 
> And lastly, I think the coupling is really showing what happens. Note 
> how the internal coupling with the NST peaks and decreases as V is 
> increased, I'm sure this is matter of the leaky shunts affecting the core.
> http://www.classictesla.com/temp/15-30nst-coupling.gif
> 
> All in all, I think the increase in voltage above and beyond is actually 
> linear from a a current stand point. I agree that using NST's above 
> their nameplate rating is common and normal. Spark gap breakdown setting 
> is of course important and dictates NST probability of failure. If a 
> moron opens up the gap beyond the NST's winding withstand voltage, then 
> the darwin award is up for a grammy!
> 
> Dex is not only wrong, but obviously very new to coiling (as you know). 
> We've been down this very path a thousand times...
> 
> Best regards,
> Bart
> 

I think it's not a coupling change, but an increase in loss as the core 
saturates.  The VA drawn from the wall increases, but the VA out from 
the secondary decreases. (with the difference going into heating the 
core)..

I've got some measurements around on a similar transformer and it shows 
a definite flattening out as the vPri went above about 130V.  The PF 
actually gets better as you go higher (because instead of looking like 
an inductor, it's now an inductor and a resistive heater).

I'd also note that the current waveform starts to get real funky and non 
sinusoidal (it gets peaks on top of the sine), so a average or rms 
reading meter may not be reading correctly.





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