Intrawinding capacitance in high turn transformers

Question

There seems to be a known phenomenon about high turns ratio transformers drawing no-load current in higher voltages with higher frequencies.

The intrawinding capacitance in the secondary (Cds in the figure above) can get high in small size high turns ratio multilayer transformers (3000 ~ 4000 of AWG 37 in this case), but how high can it get? The secondary is gonna operate up to 10 kV and I'm trying to up the frequency (in the 10s of kHz range up to 200 kHz if possible). But all of the factors here (turns, frequency and voltage) are increasing the charge and thus the no-load current draw of the converter.

What are the limits in this? Does it even get high enough to matter? Does segmenting the secondary into 10 or so segments of a couple of hundred turns each, separated by 1 or 2 millimeters of plastic help to reduce the capacitance?

Answer 1

does segmenting the secondary into 10 or so segments of a couple of hundred turns each, separated by 1 or 2 millimeters of plastic help to reduce the capacitance?

Yes

In a transformer winding, inter-turn capacitance is generally negligible compared to inter-layer capacitance.

We can approximate the winding self-capacitance within a small factor by considering only the capacitance between winding layers, approximating the layer to a conductor sheet.

The highest capacitance arrangement is when each layer is wound in opposite directions, so left to right on the first, right to left on the next. That's because the first turn of the first layer is opposite the last turn of the next layer, so there's twice the voltage per layer between those turns. As the energy stored in the self-capacitance goes as the square of the voltage, this more than offsets the lower voltage difference at the other side of the windings.

A lower capacitance can be obtained by winding each layer in the same direction, returning between layers, so left to right, then left to right again. The voltage between layers is now uniform at the per layer voltage.

To drive the capacitance still lower, the secondary should be segmented, with an airspace between segments. Disc windings can also be used, basically very many narrow layers.

Answer 2

Here are a couple of inductors used often as radio-frequency chokes. They are wound so that capacitance is minimized:

Both inductors have no ferrite cores, but this kind of winding is appropriate on ferrite. These windings are divided into segments (4-segments for the smaller one, 5-segments for the larger one) - the space between segments reduces capacitance.>br?

Each segment layer has few turns so that inter-layer capacitance is minimized. Both these use Litz wire, which attempts to distribute current flow throughout the wire ; otherwise, current tends to flow only as skin current - this can also help minimize inter-wire capacitance, at least for lower frequencies.
These wires are cotton-covered, making winding bulkier than magnet wire would be, but the thicker insulation also reduces inter-wire capacitance.

Not the easiest things to wind and keep everything in place! Perhaps you can see that windings are fixed with some kind of lacquer - which detracts from desired low-capacitance.