NST Transformer ThougHts

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi all,

With Teri Mekenney's ID of the transformer and D.C.'s info on windings*, I 
was able to "very roughly" work out the fluxes in the NST.

The transformer is an Allanson 15kV 30mA:

http://hot-streamer-dot-com/temp/TRN06.jpg

The dimensions are:

http://hot-streamer-dot-com/temp/TRN-00.gif

After the usual messy calculations:

http://hot-streamer-dot-com/temp/TRN-01.gif

One can see that the reluctances (sort of like resistance) in the outer 
path and inner path are fairly equal (given the air gaps) at ~~280 A-t/Wb:

http://hot-streamer-dot-com/temp/TRN-02.gif

When the transformer is not loaded, the flux is probably close to the 
beginnings of saturation at 120 VAC input. I would imagine that a scope 
look at the primary current of an unloaded NST shows this saturation 
beginning as peak current distortions.

http://hot-streamer-dot-com/temp/TRN-06.gif

Interestingly, the saturation seems to start right at 125VAC!  the waveform 
is always distorted like it shows though at any voltage.

The center area of the core where the primary is wound has about twice the 
flux of the rest of the core, so that is where saturation will be most 
likely to occur. The shunts are thinner but they are somewhat helped by the 
air gaps (very small). However, they are certainly next in line for saturation.

http://hot-streamer-dot-com/temp/TRN-04.gif

If the secondaries are loaded, their flux opposes that of the primary, so 
secondary load will counteract the saturation.

http://hot-streamer-dot-com/temp/TRN-03.gif

This probably explains why NSTs that are firing do not go into this 
ferrorresonance mode while NSTs run just with a cap on them do. I would 
guess that an unloaded transformer that will go into saturation at say 
140VAC will need much higher input voltage to saturate with a load on the 
secondary (I am not an expert in transformer things...).

Of course, with a cap on the output as a load, things must get very odd. I 
would guess that the secondary current would see substantial phase shift so 
that the secondary counter flux may tend to further increase saturation? At 
some point, the capacitance on the secondary and the effective inductance 
in the transformer hit a 60Hz resonance and the thing goes into this loud 
ferroresonant humming mode.

Not sure what it all means. I am certainly not an expert in this stuff so 
beware of newbi errors...

Perhaps we can sort of play with the counter flux and ferroresonance to get 
super powers out of NSTs. There is already evidence this can be done as 
shown by Gary Lau's and Gerry's coils that seem to work better than they 
"should". But right now there is no control or science behind it aside from 
good luck.

Much to ponder...

Cheers,

	Terry

*"Primary is usually 180 turns of # 16 AWG. 7125 turns per coil for 7.5kV 
on each coil." But 7125/180 gives a turns ration of 39.6. 120VAC x 39.6= 
4750 volts??