Re: Current Limiting and Impedence

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Help is at hand:

On 11 May 2005, at 11:50, Tesla list wrote:

> Original poster: Steve Conner <steve@xxxxxxxxxxxx>
>
> At 16:50 10/05/05 -0600, you wrote:
>
> >Please excuse my ignorance. Will you please define the following: Ve
> >& Ae,
>
> Yes good point, I don't know what these are either :-/

Ve is effective core volume and Ae is effective cross-sectional area
(generally == pole area).

> >Le & C (capacitance?),
>
> Nor these

Le is effective magnetic path length (mean length).

> >AL,
>
> I do know this one though, it's the inductance of a single turn
> winding on the core in question. "Specific inductance" IIRC. Once you
> know AL for a core, you can calculate the inductance of any winding
> you make on the core by multiplying AL by the number of turns squared.

Al is sometimes referred to as "induction factor". It can be easily
measured/derived for any core, gapped or ungapped and is used exactly
as you suggest.

> >10555 nH (nano henries?),
> >mT (miliTesla's?),
> >and finally, Ui, Ue, and Ur.
>
> Yup I'd like to know what Ui Ue and Ur are as well.

Ui is incremental permeability
Ue is effective permeability
Ur is relative permeability

The best source for definitions of these are ferrite core
manufacturers' data books. The Philips MA01 databook (probably long
since superceeded) does a nice job of explaining what these mean and
how they relate to inductor design. The reason so many different
defns of permeability exist is that they recognize that permeability
is not a fixed quantity but dependent on the degree of core
magnetization (e.g. core permeability progressively drops as applied
H increases). This is reflected in the B-H curves.

Hope this helps a bit. If requested and time permits I could dig the
formal definitions out of the databook in question and post to the
list.

Malcolm

> BTW I experimented with gapped MOTs a while back. As Mark mentioned,
> the Es and the Is are usually all stacked together and can easily be
> separated by two hacksaw cuts. I used trial and error, and ended up
> with an airgap of around 0.15" which gave an inductance of 32mH using
> the existing primary. (We have 240v line voltage in the UK, so our
> MOTs all have twice as many primary turns as American ones- hence four
> times the inductance- so this seems to agree with Mark's 8mH
> measurement)
>
> I never tested the saturation current except to check that it wasn't
> saturating in the application, which was a DC resonant charging choke
> for the OLTC II, passing up to 12A peak and 5A average. So I guess a
> 120V MOT gapped would be good for twice that?
>
>
> Steve Conner
>
>
>
>
>