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RE: [TCML] BPS Testing

Hi John,

> 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?

I'm sure that I completely removed the core from the windings when I depotted it.  But I have very little recollection of the core geometry.  I'm still kicking myself for not taking photos, but that was before I got my first digital camera.  I don't recall having any trouble getting the core tightly reassembled, so the laminations (with integral shunts) may have been riveted or welded together into two separable assemblies.  It sounds like your laminations were individually loose?

Regards, Gary Lau

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of FutureT@xxxxxxx
> Sent: Wednesday, March 12, 2008 9:57 PM
> To: tesla@xxxxxxxxxx
> Subject: 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
> 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.
> Cheers,
> John

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