Physics reminder: conduction currents, induced currents, eddy currents

Induced currents, eddy currents

When metallic conductors are inserted in a variable magnetic field or when they are in motion in a constant field, the result is the generation of electrical currents called induced currents or eddy currents in these conductors.

Effects of induced currents

Induced currents have a negative effect in the core of transformers. This may be reduced by using thin laminations, which prevents the propagation of these currents.

They have a positive effect in induction heating or non-destructive control applications, to dampen the oscillations of moving parts, in rotor bars of induction machines, in the secondary circuit of transformers, etc.

Induced currents, conduction currents

For the different cases analyzed, there are two possible current flows:

  • the conduction current
  • the induced current

These two possibilities are presented in the table below.

When the passing current

in the conductor …

we call this …
is imposed by an external source of current or voltage source

conduction current

(the conductor is supplied directly by a current or a voltage source)

is the result of the variation in time of the magnetic flux density, viz. of Faraday law:

induced current :

(the conductor is supplied indirectly “by induction”)

Example of a transformer

In a transformer we distinguish:

  • conduction currents in the primary winding, copper or aluminum
  • induced currents in the secondary winding, copper or aluminum
  • eddy currents in the laminations of the magnetic circuit.