GDT design

[flyingperson23]

I'm designing a big coil, and a point was brought up - during operation, full bus voltage is across a pair of gdt windings at all times. I'm hoping to use a boost converter for a bus around 1200v and cat5 wires have 300v insulation, so I don't want to risk a gdt flashover destroying my igbt gates. Are there any other cable standards like cat5 but rated for a sufficiently high voltage, or will I have to use individual wires?

[Mads Barnkob]

Perhaps some multi core control cable like LIYY 8x0.25 could be used, its 6.2mm outer diameter and would properly require a larger core, than if you used cat5 cable.

It has a voltage rating of 500V.

https://www.tme.eu/dk/en/details/liyy-8x0.25/multicore-cables-unshielded/lapp/0028308/

There do also exist 300V, 600V and 1000V Ethernet cable, but I think its only the outer insulation that goes for that rating, as to which other cables you are allowed to mix it with in a cable tray.

Maybe you could wind two ethernet cables on the same core, one cable for the primary (all wires connected together for 1 winding) and the other cable for 4 pairs of two wires in parallel. But the leakage inductance might get too high from low coupling.

[davekni]

I'm hoping to use a boost converter for a bus around 1200v

Wow, what voltage rating are your IGBTs?

People regularly use 300V cable for 560Vbus with whatever spike voltage occurs above that.  Insulation rating is for long term exposure and high reliability.  However, 1200V may be too high for 300V wire, especially if you want low risk and your coil will be used frequently.
Probably easiest to find suitable individual wire.  I'd still recommend twisting that wire into 4 pairs, paralleling one wire of each pair to form primary.  Will minimize leakage inductance.

[flyingperson23]

I'm using 1700v igbts (ff1000). I am using a ud3.1 so I'll need 2 GDTs so wire diameter will be less of an issue, I just need to find suitable wire.

[Hydron]

You could wind the GDTs with something like RG-174 or similar small diameter coax - voltage rating should be >1kV (look it up for whatever cable you find) and you can run the primary winding on the shield and the secondary on the core for very high coupling (low leakage).