# Describing conducting media

## Magneto Static / Transient Magnetic distinction

The Transient Magnetic application mainly is different from the Magneto Static application by the possibility of taking into account:

• on the one hand, variable (in time) current sources
• on the other hand, induced currents which can appear in conducting regions…

In the Magneto Static application:

Electrical currents in conductors are continuous conduction currents (no variation in time) and the distribution of the current in the conductor section is uniform (J constant / no space variation).

In the Transient Magnetic application:

Electrical currents in conductors can be:

• variable conduction currents (sinusoidal, trapezoidal…)
• induced currents

In addition, the current distribution in the conductor section can be:

• uniform (constant J): negligible skin effect, no proximity effect
• non-uniform (non-constant J): skin effect / considerable proximity effect

## Examples

Examples of different physical cases are presented in the table below.

Current Skin effect Example
conduction current

negligible (uniform J)

Thin wire type coils of a transformer primary winding

present Bus bars…
induced or eddy current

negligible (uniform J)

Thin wire type coils of a transformer secondary winding

present Rotor bars of an induction machine, Laminations of a transformer magnetic core

## Types of conductors in Flux

In order to model the different physical cases previously described there are different types of conductors. Different conductors in Flux are described below*.

• A coil conductor (or coil) is a current carrying conductor where the skin effect is negligible because the diameter of the elementary insulated wires is small with respect to the skin depth. The current density is considered constant on the whole section of this type of conductor.
• A solid conductor is a conductor (bar, thick strip) in which the skin effect is evident. The current density is not uniform on the conductor cross-section.

## Difference between active and passive conductor

A conductor is considered (in Flux 3D):

• passive if the current in this conductor is supplied indirectly (by Faraday law).
• active, if the current in this conductor is supplied directly (by a current or a voltage source)

## Examples

Examples of different conductor types are presented in the table below.

Flux conductors Current Example
Stranded conductor active conduction Primary coils of a transformer
passive induced Secondary coils of a transformer
Solid conductor active conduction solid bus-bars
passive induced Rotor bars of an induction machine, laminations of a transformer