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"flux cancelling windings" ?

Hi all, I noted the following (below) on a website. What is Nc? Number of turns compared to what? I want to improve a transformer with very low capacitance between the pri and sec, this might help improve the coupling while maintaning the low capacitance. Do you have any more information on this technique? Thanks Mike K.

It is also possible to reduce leakage using a pair of "flux cancelling"

windings, each with Nc turns. Wind Nc turns first on bobbin. Then wind transformer. Then wind Nc turns (so one winding is "inside" the other "outside"). Connect the windings in parallel. Because the inner and outer windings have different flux linkages due to leakage, current will flow thereby creating a flux which counters the imbalance.

this trick gets used in HV transformers, where the secondary is a >triangular profile to minimise capacitance (and keep HV the hell away) >and a split primary is generally not used.
Reply to
amdxjunk
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Can you provide a link so we can see it for ourselves?

Reply to
The Phantom

The website is just a repeat of threads from newsgroups.

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Third letter down, I think. I sent a letter to the author of the info but have not received a reply. Mike

Reply to
amdxjunk

He posts here regularly. Maybe we can get his attention.

Reply to
The Phantom

Nc doesn't matter, as the "Nc" windings are just shorted out anyway. Could be a single turn of foil for each (as long as the external links were of similar low resistance.

But bear >Hi all,

Tony (remove the "_" to reply by email)

Reply to
Tony

ya have now :)

probably not. He's notoriously unobservant :)

"Rise Time Reduction in High-Voltage Pulse Transformers Using Auxiliary Windings, L.M. Redondo, E. Margato, J.F. Silva, IEEE Trans. Power Electronics Vol. 17 No. 2 March 2002

I have not tried this myself, but the paper is a good read. They used a transformer with:

Np = 50 Ns = 506 Nc = 25T (they call it Naux)

The xfmr had double P-S insulation and "staircase" secondary construction to reduce capacitance. They play around with various resistances connecting the two Nc windings.

Cheers Terry

Reply to
Terry Given

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