Determination of evaluated resistance of stranded coil conductor

Dr. Mandy Bauch

Dear all,

 

I have a question about stranded coil conductors using non-meshed coils. I have performed two transient simulations with non-meshed coils in 3D for a transverse flux machine. For the first simulation I entered 100 mOhm in the field 'Resistance Formula' of the stranded conductor. For the second simulation I entered 5 mOhm. The geometry as well as the material parameters and number of turns were the same for both simulations. For both simulations, the non-meshed coil was part of an electric circuit.
I assumed that the resistance value is calculated via FLUX using the resistance formula R=rho*l/A and that the value entered in the 'Resistance Formula' field (stranded coil conductor) does not matter if the specific resistance as well as the fill factor are specified for the non-meshed coil. However, the result for the evaluated resistance is different for both simulations. 

 

Preset value of 100 mOhm --> evaluated resistance = 106 mOhm

Preset value of 5 mOhm --> evaluated resistance = 11 mOhm

 

The evaluated resistance of the non-meshed coil is the same for both simulations: 3 mOhm. Why is there a difference between the evaluated value of the non-meshed coil and of the stranded conductor? I assumed, this should be the same?

 

Therefore, could you please tell me, how the evaluated resistance of the stranded coil conductor is determined? Is it important, to enter the 'right' value in the field 'resistance formula'?

 

Thank you in advance and best regards,

Mandy

Alejandro Rodríguez

Dear Mandy,

Actually, most of your assumptions are right: the resistance value is calculated by Flux using the equation  R=rho*l/A. What it is not right is that, in this case, the value entered in “resistance formula” does not matter.

In fact, total resistance associated with stranded coil conductor is the addition of two terms: the one calculated using R=rho*l/A and the value introduced by the user. In other words, value introduced in “resistance formula” field is an additional source of resistance added to the one obtained from geometrical and material properties.

In your case, the resistance calculated from geometry is 6 mohm, as can be deduced from your outputs. If evaluated resistance of the non-meshed coils is only 3mohm and not 6 it is maybe due to the existence of symmetries/periodicities or maybe because two coils are associated to the same stranded coil conductor.

From a practical point of view: If you only want to take into account the value calculated by Flux from material and geometrical properties (i.e., R=rho*l/(F*A), where F is the fill factor) you should write 0 in “resistance formula” field. On the contrary, if you want to establish yourself the resistance in spite of geometry/material properties, the best way to do so is not to fill the field “material” when defining the non-meshed coil.

Best regards,

Alejandro