Anchor (electrical engineering)

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Shaft with applied drum armature; in the foreground the commutator

In electrical engineering, the rotor ( rotor ) of DC machines and single-phase series motors (universal motor ) or the electrically active part of the rotor is referred to as the armature in the narrower sense . The rotating armature is usually surrounded by a stationary stator (stator) and only separated from it by a fine air gap. The forces arising between the armature winding and the excitation winding housed in the stator during operation lead to a rotary movement of the armature and the shaft rigidly connected to it.

In contrast, the rotor of the three-phase synchronous machine , designed as an internal pole machine , is called a pole wheel . In this case, the stationary stator winding of the stator is called the armature winding. The term “armature” is not specified for asynchronous machines , as mutual voltage induction occurs between the rotor and stator windings. In this type of machine, the rotor is called a squirrel-cage rotor .

The moving iron core of electrical relays , contactors and electromagnets is still referred to as the armature .


Sketch of a ring armature in the stator field

The usually cylindrical armature consists of mutually electrically insulated and layered electrical steel sheets in order to keep the eddy currents in the armature caused by the stator field low. Distributed over the circumference, grooves are let into the electrical steel sheet along the shaft , which accommodate the armature winding. Depending on the construction towards the surface, the grooves can be closed with wedges in order to prevent the armature winding from loosening due to the centrifugal forces .

Enameled copper wire is used to manufacture the armature winding of small DC machines . In larger DC machines, electrically insulated copper bars , so-called Roebel bars , are inserted into the grooves of the armature. The commutator is located directly in front of the armature winding on the shaft . The contacts of the commutator are connected to the winding ends of the armature winding. The entire construction is attached to the shaft by means of press rings.

Armature winding companies are traditionally companies that manufacture or repair armature or rewind armature windings.

There are different types of armature windings.

Double-T anchor

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

Ring anchor

Sectional view of a ring anchor according to Gramme.
A) Iron wire for field guidance
B) Segments of the ring
armature winding R) Carrier material for fastening the armature to the shaft

The ring anchor was used by Zénobe Gramme in 1871 . A ring armature consists of a magnetically highly conductive carrier material made of electrical steel (shown as a ring in the sketch on the right), around which the armature winding is guided in a spiral. Iron wire was used in historical designs such as the DC machine from Zénobe Gramme.

The ring armature winding has several taps around the circumference, which are led to the contacts of the commutator. In the sketch, brushes are indicated in the upper and lower areas. The ring armature winding is structurally disadvantageous since the individual turns inside the ring do not contribute anything to the generation of torque. This disadvantage is eliminated by the construction of the drum anchor.

Drum anchor

Development scheme for a drum armature with wave winding; the pole pitch in this case is 180 °

The drum armature was developed by Friedrich von Hefner-Alteneck in 1872 and is still the most common type of armature in DC machines today.

In a drum armature winding, the individual turns are guided along the grooves on the outer surface of the armature. The return line of each turn is not routed inside the armature, as is the case with the ring armature, but offset on the circumference around the pole pitch of the stator. As a result, compared to the ring armature, twice the voltage is induced in each turn of the drum armature. Depending on the number of pole pairs of the stator, there is a certain armature winding scheme, as shown in the illustration on the right for the number of pole pairs of 1.

Individual evidence

  1. Ekbert Hering, Rolf Martin, Martin Stohrer: Physics for engineers . 8th edition. Springer, Berlin Heidelberg New York 2002, ISBN 3-540-42964-6 .
  2. Werner M. Köhler: Relay basics, designs and circuit technology . 2nd Edition. Franzis-Verlag, Munich 1978, ISBN 3-7723-1602-6 .
  3. Fritz Raskop: The catechism for anchor wrapping. Guide to the manufacture of windings on electrical machines, transformers and high voltage equipment . 15th edition. Frankfurter Fachverlag, 1976, ISBN 3-87234-018-2 .


  • Gerd Fehmel, Horst Flachmann, Otto Mai: The master's examination in electrical machines. 12th edition, Vogel Buchverlag, Oldenburg and Würzburg, 2000, ISBN 3-8023-1795-5
  • 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