Re: OLTC inductances

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Antonio,

When I made my OLTC I had no idea what the primary inductance would be for 
the three parallel loops in the primary.  With your program this is now 
solved :-))

My primary measures 404.5nH and Inca gives 398.3nH.  Any error is probably 
due to my not measuring it just right or the close proximity of the primary 
caps, IGBTs and other stuff.

Many thanks for another great tool!!

Cheers,

         Terry


At 02:50 PM 4/12/2003 -0300, you wrote:
>Hi:
>
>I made an adaptation in my "Inca" inductance calculator to allow
>the analysis of transformers with all the primary turns in parallel,
>as those used in the recent OLTC coils.
>The procedure is as follows:
>1)The program computes the inductance matrix of the system, considering
>v circular turns in the primary, that can be a general conical coil,
>and a solenoidal secondary coil. Explicit precise formulas by Maxwell
>and John Viriamu Jones, based on elliptic integrals, are used.
>This keeps high precision even for very strange coils, and is fast.
>The matrix has v+1 rows and columns, with the last corresponding to
>the secondary coil and its coupling to the individual turns. The matrix
>is listed if the number of turns is small.
>2)The matrix is inverted, and the first v lines and columns are added.
>This corresponds to the application of a common voltage over all the
>primary turns, and the addition of the currents in all the primary
>turns.
>3)The resulting 2x2 matrix is inverted again. The result is the two
>equivalent inductances and the final mutual inductance.
>
>So far, the results look consistent. The coupling coefficient is
>about the same for a spiral primary coil, but the inductance of the
>primary coil is smaller than an one turn inductance. It tends to
>a current sheet inductance with 1 turn, that Wheeler's formula
>approximates quite well. A curiosity is that the secondary inductance
>is slightly decreased, due to the "shorted turn" effect caused by the
>different mutual inductances between the interconnected primary
>turns and the secondary coil.
>
>A problem is that uniform secondary current is still assumed.
>The effective coupling coefficient in a real coil will be a bit
>higher due to current concentration at the bottom section of the
>secondary coil.
>
>The program is at: http://www.coe.ufrj.br/~acmq/programs
>
>Antonio Carlos M. de Queiroz