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Re: [TCML] BPS Testing

In a message dated 3/11/2008 9:49:35 P.M. US Eastern Standard Time,  
bartb@xxxxxxxxxxxxxxxx writes:

>Hi John,

>I understand the type of tear-apart you did. If  you leave out 
>laminations, it will enter saturation with less current  (at which point 
>since the core cannot absorb any further, it saturates  and current can 
>then go very high). I expect saturation occurred  earlier and then went 
>into heavy currents (the transformer should have  felt a little warm 
>after running it if this was the case). The potting  itself should not 
>affect current (other than a heat dissipation  variation), but 
>laminations certainly would. Given that NST hv  windings are so sensitive 
>to over-voltage, it wouldn't surprise me if  the core was also on the 
>ragged edge by design.

>Take  care,

Bart, Gary, 
The core is about 2" thick with all the  laminations.  The 
laminations are 0.015" thick each.  I left out
about 3 laminations, so that would be 0.045" missing out of  2",
which is about 2.25% of the thickness.  I  wouldn't
expect that to make much difference in the current draw,
and saturation even if the core is right on the edge of saturation,
but maybe it could.  Actually at 140VAC all NST's are in
saturation to some degree.   
In support of this view, I have another NST which is the robust  
12/30 NST which I use on the TT-42 coil.  I also depotted it
and left out a few laminations.  In this case I was using the
NST on the same coil both before and after the depotting, and
I didn't notice any change in performance or current draw after
the depotting.  The NST was robust (extra powerful) both  before
and after the depotting.  There might have been a slight 
difference in current draw which was too difficult to measure
using my meters.  
It's possible that some NST's might be affected differently
by small changes in the number of laminations or how well
the core pieces go back together.  I have no way of knowing
this for sure.   
My previous posting was mostly to suggest that Gary Lau's
15/60 Jefferson might not be the only Jefferson which draws a
lot of current since mine drew 25 amps.  It's possible the
depotting had some effect, but I don't have any information 
on the before and after behavior when used on the same TC
for that NST unfortunately.
Gary, when you depotted the NST, did you disassemble the
core and slide the straight core off of the laminated frame?
Or did you leave the core intact and just soak it to clean it?
Regarding 140VAC operation for NST's, this does tend to
put them into saturation to some degree.  This is true for 
pole pigs as well.  Both of my depotted NST's run hot, but
my un-depotted NST's run hot also at 140VAC in TC use. 

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