Question How can I model a conductor bundle in HIFREQ?
Answer To model a bundle of conductors, you could in principle model each one of them independently, although you would quickly exceed reasonnable limits in terms of memory usage. In many cases, it is possible to use a simplified model for the bundle and therefore reduce memory usage.
The effects of the separate conductors in the bundle on the computed electromagnetic fields should be quite negligible for computation points located a few bundle diameters away from the bundle. If you are interested in computing the fields at points that are not too close to the bundle, you can represent the entire bundle by a single conductor. On the other hand, the electromagnetic fields are affected by the current distribution in the network, which is in turn influenced by the impedance of the conductors. Note that this influence is often negligible, since other, larger impedances are present in the network. However, in cases where this impedance cannot be neglected, you can use the following approach to obtain a pretty good approximation.
An approximate way to model a bundle is to use a hollow conductor in HIFREQ. Setting the outer radius of the conductor to be equal to that of the bundle gives roughly the right inductance and capacitance. Choosing the inner radius of the conductor so that the surface area of a cross-section of the hollow conductor is equal to the total surface area of all the conductors in the bundle reproduces the correct DC impedance. The total impedance should therefore be reproduced quite well for frequencies that are not too high (tens of kHz).