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

Re: [TCML] Toroid question

Hi Dex,
Ok, but the NST is no ordinary run of the mill tranny. It's designed for high leakage as opposed to most other types of tranny's. I'm not saying Jim is wrong or that I'm right, but rather that I'm not sure. Jim brings up a very good point regarding losses. Those losses would be seen as the core heads further into saturation and would affect the short circuit current (this much is obvious). But regardless of the mechanism, the current in the core and in the shunts may affect the effective inductance in a similar manner as currents in a Tesla secondary are affected by frequency (current bunching) and this can in turn may affect coupling (as it is a function of L which is a function of current in the windings). Similar may occur in secondary coils also (but a different topic). Has anyone really measured that? Doubt it!
BTW, this message developed into an NST's physics when driven over it's nameplate rating by Gary. I replied and changed the subject to NST Linearity following Jim's reply. That would have been the post to reply to so that the title "Toroid Question" is differentiated as the subject changed within the post. I was not telling people to over-go their voltage, but rather the measurements I have made in this situation (and nothing more). 

Regards,
Bart B. Anderson
Modesto, CA USA

Dex Dexter wrote:

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. 





_____________________________________________________________
Washington DC's Largest FREE Email service. ---> http://www.DCemail.com ---> A Washington Online Community Member --->
http://www.DCpages.com
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla


_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla