Armature (electrical engineering)

As anchor ( universal motor ), the movable part of the rotor ( rotor) is in electrical engineering in the narrow sense in DC machines and single-phase series motors called, which is mounted on the rotating shaft and is usually within the fixed stator (stator ) is located. The resulting operating between the armature and the stator field winding is accommodated in the forces cause a rotational movement of the armature and the shaft is rigidly connected.

The rotor of the three-phase synchronous machine, designed as a revolving field, however, is referred to as a flywheel and refers to the housed in the stator stationary stator winding as an armature winding. With induction, the concept of the anchor is not fixed, since a mutual induction voltage between rotor and stator winding occurs. The rotor is referred to in this type of machine and squirrel cage.

An anchor of the movable iron core is further indicated by electric relays, contactors and the electromagnet.

Construction

The armature usually consists of cylindrically constructed mutually electrically insulated and layered constructed electric plates to keep the problems caused by the stator field, eddy currents in the armature low. Distributed over the periphery, grooves are introduced into the electrical steel sheet along the shaft, which receive the armature winding. As a function of the design to the surface, the grooves may be closed with wedges, in order to prevent detachment of the armature winding by the Fliehkäfte. In small DC motors is used for the manufacture of the armature winding of enamelled copper wire for the application. At larger DC machines electrically isolated copper rods are inserted in the slots of the armature. Immediately prior to the armature winding on the shaft is the commutator. The contacts of the commutator are connected to the winding ends of the armature winding. The entire construction is fastened by means of press rings on the shaft.

We distinguish between different types of armature windings.

A double T - anchor

The double T- anchor is the simplest design of an anchor and was invented in 1856 by Werner Siemens. The company logo of Robert Bosch GmbH includes the stylized image of a section of I- anchor.

Ring beam

The ring beam was used in 1871 Zénobe frames. A ring beam consists of a magnetically highly conductive support material from electrical sheet, shown in the right diagram of a ring around which the spiral armature winding is performed. For historical designs such as in the DC machine Zénobe grams of iron wire was used.

The ring armature winding includes circumferentially at a plurality of taps, which are guided to the contacts of the commutator. In the sketch brushes are schematically illustrated in the upper and lower range. Structurally, the ring armature winding disadvantageous because the individual windings contribute inside the ring nothing for torque generation. This disadvantage is eliminated by the construction of the drum armature.

Drum anchor

The drum anchor was developed in 1872 by Friedrich von Hefner - Alteneck and is still the most common anchor design in DC machines.

With a drum armature winding the individual turns along the grooves on the outer surface of the armature can be guided. The return line of each turn is not out as the ring beam inside the anchor, but are offset circumferentially around the pole pitch of the stator. Thereby, compared to the anchor ring, the double voltage induced in each winding of the anchor drum. Depending on the number of pole pairs of the stator results in a given armature winding scheme as it is exemplified for the number of pole pairs 1 in the right figure.