Thanks soldar for sharing
Actually I should design it and send the instruction for manufacturing, it's my customer needs. also I have a 3D printer, so I can make a custom designed bobbin for the sample.
I have a variac too, so I do not think building the sample would be a huge step for me, I can have control on things.
If you measured 275mH, then the transformer is either bad or it's a measurement error. Perhaps the frequency was 100kHz, rather than 100Hz?
Why not just buy one? 6kV of isolation is on the high side, but should be doable. Is it 6kV peak or RMS?
It's not a measurement error, I have measured it with my good Latron RLC meter,
Also the isolation is for a 6KV peak voltage, I have built a 3K boost converter before, with the diode,cap multiplier combination, I can increase it's output or build two of them and use it for testing the isolation.