Margin tape is one commercial technique. If gaps in the outer leg(s) can be managed, then sharing the gap amongst centre and legs reduces the gap length of each gap. Moving the gap to the end of the leg may be another option. But in general, commercial standard core options are typically limited.
Ahh yes margin tape would work much better than tube, unfortunately I don't have any as I have moved over to using TIW (Triple Insulated Wire) for all my high voltage transformers. Yup getting hold of gapped cores is very difficult and expensive BUT the gaps are precision compared with DIY solutions, also gapping the outer legs increases EMI considerably and that is probably my worst enemy. Always useful to know what the professional solutions are 🙂
Indeed, and it makes the gap much more undetermined, due to the enormous amount of fringe field.
Be aware that your solution, although certainly effective, does have some perhaps unexpected side-effects: the turns in the vicinity of the gap help to contain the fringe field; of course, they cannot contain it completely, which is why your solution is effective, but moving them farther away also move the fringe's reach.
In an ideal situation, all the ampere-turns would be concentrated in a single sheet tightly wrapping the center leg, and all the fringe fields would disappear.
In practice, this is not possible, and some trade offs have be found, but it is good to keep in mind the underlying problems
Ahh, now I recall another 'exotic' technique for alleviating the affect of one substantial gap - use a centre core with multiple gaps. Each gap, being a smaller width, splays out less fringing flux - which the former seperation then has more of a chance to alleviate any effect on nearby windings.
Ohh no I am not hitting my expensive cores with a hammer 😀 and how to stop the bits chattering, immerse the assemblage in epoxy ? I do appreciate your contribution it just made me laugh a little 🙂
Using half gap in the center tongue and in the outer legs increases EMI (Radiated field) monstrously, I suggest not to use this technique.
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