Best Wire for Step-up Transformer?

[TheMadHatter]

Looking at making a push pull step up transformer from a large U core (~3-4in legs). The core should be able to do ~10kW in a push pull, I only need 1kw. So my winding window is underutilized.
I'm wondering for a ~50kHz switch mode transformer, what wire type would offer the best insulation at this of frequency? I plan to have a 5 section bobbin, with a minimum 10kv output, so 2kv per bobbin section.
Historically with fly-backs and push pulls I have constructed on EE cores, even with silicone 3kv wire, I see breakdown and arc over at <1kv around 100kHz.

The only realistic options I see are below:

• Magnetic Wire (breakdown numbers I have been seeing are unrealistic based on experience, 7kv for #28AWG?)
• Silicone high voltage wire (eBay has cheap 3kv and 6kv class wire)

I'm going to continue looking for papers etc. on breakdown resistance vs frequency for these options, but I figured I would ask here as well.

[rikkitikkitavi]

Cheap 3kV silicone wire is just that, cheap and not 3kV insulation.
It has a single insulating cover of silicone which maybe theoretically can withstand 3kV.
But at higher frequencies insulation voltage decreases, and imperfections means the insulation breakdown is less.

Also, the thick single layer insulation is thermally an insulation.

There is nothing wrong in using ordinary PU insulated wire with say 500V insulation, but the layout of the secondaries have to be adjusted. Ie layer to layer voltage, voltage between layers,  creapage and so on. Air insulation is more prone to breakdowns.

Alternativly you could go for a renown brand of tripple insulated wire, UL approved or by other standards. Especially if it is Med Tech approved. It typically have a tested breakdown in the range of 3000-4000Vrms, at 50/60 Hz .
But insulation is often ETFE (Tefzel) or similar which have excellent HF properties in the typical range of switching devices.

It is not cheap however but compared to a 3-4 inch center core , well...