Discussion Forum

August 23, 2010 8:46am UTC

Coil with litz wire in 3D

Hi all,

i am currently looking into simulating coils in 3D. We are going to use litz wire to reduce skin effect. I know that there are new single and multi turn coil BC for 4.0x that can be used for 2D or axialsymmetric set-up, but for a true 3D model, what would you do?

Setting up the litz wire as true geometry seems somewhat impractical...

Regards,
Matthias

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

August 23, 2010 11:15am UTC in response to Ivar Kjelberg

Re: Coil with litz wire in 3D

Just some clarifications and further thinking:

I am going to model the individual turns as geometry anyway, because there are only few, and we have to look at near-field effects.

But what about the skin and proximity effects within the single strands of a single turn? The strand diameter is of the order of the skin effect depth.

One important difference is that the strands in the litz wire are connected in parallel, while the turns of the coil are in series. That would make it necessary that literature like Meekers "Continuum Representation of Wound Coils via an Equivalent Foil Approach" would have to be reworked if I'd like to apply it to a single turn out of my multi-turn coil.

Or am I to complicated here, would something like

sigma_effective = sigma_copper / number_of_strands

do the thing? Probably not, because then skin effect still would be way to large.

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

August 24, 2010 4:51am UTC in response to Ivar Kjelberg

Re: Coil with litz wire in 3D

Hi Ivar,

thanks for your reply.

We are going for real high frequency litz wire, where the single strands are individually isolated, so inter-strand surface resistance is no matter here.

It boils down to a massive parallel connection of tiny strands wound into a coil.

Good hf litz wire follows well-designed patterns to make sure that each strand stays the same length on each position in the cable, averaging out all inner-outer-differences.

I'd say that since the single strand is in terms of diameter similar to the skin effect depth at our frequency (20-100 kHz), I'd totally neglect skin effect.

But I am still not sure about the proximity effect. And if we have no skin, but proximity effects, how to model it? Physically it's the same, but arises from different sources of the field.

Still thinking,

Matthias

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse