RE: [TCML] Permanent Magnet GDT(?)

[Christopher Karr <chriskarr4@xxxxxxxxxxx>]

Thank you, everyone, for explaining these things to me. I expected it wouldn't work, though I didn't expect it to be such a large effect. Perhaps using a high-permeability core with a biasing winding might be superior. I'll do some experimentation.

Happy coiling,

 - Christopher

> Date: Tue, 31 May 2011 10:59:30 -0500
> Subject: Re: [TCML] Permanent Magnet GDT(?)
> From: steve.ward@xxxxxxxxx
> To: tesla@xxxxxxxxxx
> 
> Christopher,
> 
> This will not work as you expect.  Because of the field orientation within
> the material itself, the permeability is very low (ideally near 1), whereas
> un-saturated ferrite is often a permeability of a few thousand.  So unless
> your magnetizing force (amp-turns) is very large, the core will not offer
> much permeability, and consequently the leakage inductance will be large,
> and the magnetizing inductance will be small, which makes for a poorly
> performing GDT.
> 
> from your other email you said:
> 
> "I understand that the magnetic material is already close to saturation
> when fully magnetized, as in a permanent magnet, but can that nearness
> to saturation not be reversed by applying an opposition to the current
> magnetic field?"
> 
> True, but you need a lot of field to do that, as permanent magnets are as
> saturated as they get typically.  You wouldnt normally ever run a
> transformer on that part of the B-H curve, its pointless because the slope
> says the permeability is near 1.
> 
> I think that also, the material type is specifically designed to have a
> large hysteresis, such that it *retains* its magnetism after the original
> magnetizing force is removed.  This would be another big strike against it
> in terms of using this material as a transformer, the energy loss per cycle
> would be problematic.
> 
> Steve
> 
> On Mon, May 30, 2011 at 2:48 PM, Christopher Karr <chriskarr4@xxxxxxxxxxx>wrote:
> 
> >
> > Good day, Everyone,
> >
> > I've been pondering this topic for some time, now, and I've been wondering
> > if it were reasonable to use a ferrite permanent magnet (in toroidal shape)
> > as a core for a GDT.
> >
> >
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