Litz AC resistance approximation in PEmag

[juhani.stenback]

Hello,

When using Litz wire, does PEmag take the proximity effect into account when calculating the AC resistance for a transformer? Some documents would indicate that PEmag always takes the proximity effect into account when calculating AC resistances for a winding, but my results indicate otherwise. 

One document I found states that Twisted wire could be used to model every strand of a Litz conductor for the actual skin and proximity effects in PEmag. My tests confirmed that there was a significant difference between the AC resistances when simulating the following cases using twisted wire: 1) where two turns were positioned directly next to each other on a toroidal core, 2) where the same two turns were positioned on opposing sides of the core. When simulating the same models with Litz wire, the resulting resistances were exactly the same. 

Is there a possible fix for this? Or is it just so that PEmag cannot take the proximity of the turns into account, when the wire is modelled as an "equivalent Litz bundle" (as described in a document found on this page). If twisted wire could be used to model the proximity effects in transformer windings when using Litz wire, how could one do that? 

Thank you in advance for all the help. 

Best regards,

Juhani