Air gap (magnetism)

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As the air gap in which is electrical in the context of magnetic circuits the space or distance between two opposite faces referred to which a magnetic flux lead. Examples are the air gap between the rotor and stator of an electric motor or the air gap in reactors . With some technical devices such as transformers , efforts are made to keep the air gap as small as possible for the most efficient function possible.

Iron core with air gap
Pole piece of a salient pole machine ; the shape shown in green leads to an inhomogeneous magnetic flux density in the air gap, the one in orange to a homogeneous one

An air gap in the otherwise closed course of an iron core or ferrite core increases the magnetic resistance in the magnetic circuit. The inductance for a magnetic circuit with an air gap is calculated as follows:

The magnetic saturation of the core material occurs only at significantly higher field strengths. A substantial part of the magnetic energy is stored in the air gap of storage chokes. For this, it must be accepted that the inductance per number of turns (so-called Al value) is reduced.

Even if this gap does not consist of air, it is still called an air gap; The absence of ferromagnetic material is interesting for the effect. Depending on the component's function, high forces occur there (e.g. in the case of inductors); if necessary, dimensional accuracy and wear resistance are decisive (e.g. with magnetic heads ). Therefore air gaps are often built from solid (non-ferromagnetic) material; this reduces noise (e.g. mains hum ) and changes in the gap width.

In the case of direct current relays , an air gap prevents the armature from sticking to the coil core, since a small residual magnetization is retained even when the coil is de-energized. It is filled here with a non-ferromagnetic rivet or foil.

Powder cores consist of many separate ferromagnetic particles, which is also referred to as a distributed air gap.

literature

  • Gregor D. Häberle, Heinz O. Häberle: Transformers and electrical machines in power engineering systems . 2nd Edition. Verlag - Europa - Lehrmittel, Haan-Gruiten 1990, ISBN 3-8085-5002-3 .
  • Karl-Heinz Dietsche, Thomas Jäger: Robert Bosch GmbH: Kraftfahrtechnisches Taschenbuch . 25th edition. Friedr. Vieweg & Sohn Verlag, Wiesbaden 2003, ISBN 3-528-23876-3 .
  • Winfrid Hauke, Rolf Thaele, Günter Reck: RWE Energie Bau-Handbuch . 12th edition. Energie-Verlag GmbH, Heidelberg 1998, ISBN 3-87200-700-9 .