Rotary transformer

A rotary transformer, referred to in particular for magnetic recording devices, as the head drum is in electrical engineering, a special design of a transformer, wherein the primary side towards the secondary side, can be rotated mechanically free. The application is primarily in the field at the magnetic data records for data transmission using helical recording as video recorders or digital data storage, where the designated as the head drum rotation transformer is used to bring the signals to the rotating write and read head. Other applications range from space probes, where rotary transformers of energy and signal transmission between each other rotating parts are used.

The alternative to Rotionstransformatoren are slip rings as opposed to rotary transformers also can transfer DC voltage, however, are subject to more wear slip rings and therefore have a shorter service time on.


A rotary transformer consists of two parts: a stationary stator fixed to the first winding ( in the adjacent figure blue) and one to rotating on an axis rotor with the second winding ( red). For guiding the magnetic flux Φ between the two windings is used, as in a conventional transformer, in accordance with a mechanically Enriched core surrounding the windings, and the two halves ( stator and rotor ) is divided. By this division, and the resulting air gap existing between the fixed and rotating core half, these transformers to a relatively high magnetic flux leakage.

Rotary transformers are used, as opposed to electric motors, which also include a stator and rotor not to generate mechanical forces due to the magnetic field or to be transmitted. A possible drive, to move the rotor into a mechanical rotary movement, is independent of the transformer. In certain cases, such as head drums with VCRs, the drive is absolutely integral with the head drum.

Rotary transformers can be used both for energy transfer from AC voltage, and therefore the data and signal transmission. The head drums in magnetic recording devices with helical scanning are usually for multiple, mutually provided separate transmission paths. Are usual two to six parallel transmission paths which lead to the individual read heads to the outside of the head drum. The various windings are arranged in concentric circles around the axis to influence each other as little as possible.

  • Head drum of a video recorder

Stator of a head drum in a video recorder with the mirror image lying fixed windings