Develop

for eddy current of eddy currents, if one an electrically conductive material like e.g. Metal in a magnetic field moves or a such material in a temporally changing magnetic field is. More exactly said an eddy current develops, if the magnetic river changes by this workpiece.

Becomes in thisMaterial due to the high mobility of the free charge carriers a tension induces. Develop dependent on the specific electrical resistance in itself closed eddies flows. These again produce an opposite magnetic field for the cause (thus the original magnetic field) according to the Lenz rule.

applications of theEddy current principle

one of most important applications of the eddy current principle takes place in three-phase alternating current synchronous engines, whose rotor is a metal cage. In this metal cage develop eddy currents, which are induced by the magnetic rotary field of the stator coils. The interconnection of the stator rotary field with the squirrel-cage rotor - field leads to the rotating motion of the rotor.

Thoseto most common application of the eddy current principle the screening effect of metallic housings is against electrical and magnetic alternating fields. With the impact of these fields in the housing eddy currents are induced, whose own field partly compensates the hitting.

Further applications are the eddy current brake with course vehicles, the eddy current absorption in raster tunnel microscopes or the inductive heating of metal (e.g. in melting furnaces, induction cook fields) and the eddy current inspection during the non destructive material testing and material characterisation (for example separation of aluminum with the garbage recycling). Furthermore also simple small engines have an eddy current drive, like the turntable in electric meters, consisting of aluminum according to Ferraris - the principle.

eddy current as lossy accompaniment

frequent is the eddy current an unwanted accompaniment, which leads to losses when simultaneous strong heating up. For this reason the magnet cores are not built by transformers and electric motors substantial, but from individual thin (some tenths of a millimeter),of each other electrically isolated sheet metals compound (“geblecht”). The orientation of the bundles of laminations selected thereby in such a way that the magnetic lines of flux are not obstructed, the eddy current courses however as high a resistance as possible to possess. The sheet metals in the magnet cores provide also for the typical “transformer humming”.

Soft-magnetic materials become thusapplication-oriented (e.g. dependent on the working frequency) also after the specific electrical resistance selected, in order to minimize the eddy currents. Sheet metal for large transformers e.g. exists. from 3% silicon irons (ρ = 0.4 Ω · mm ² /m) instead of from pure irons (ρ = 0.13 Ω · mm ² /m). AnotherCounter measure is the use of sintered /gepressten soft-magnetic powder materials (ferrites), with which the powder grains are individually isolated. Here then of the material determines, also the grain size of the powder substantially the occurrence of eddy currents except the conductivity. Throttles become special with powder cores of different alloysand grain size developed.

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