Dahlander motor

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A Dahlander motor is a circuit variant of a three-phase asynchronous machine for switching between different speeds . The circuit is named after Robert Dahlander (1870–1935).

Layout and function

Dahlander circuit for low (triangle) and high speed (double star)

With the Dahlander circuit, the number of poles of the asynchronous machine (pole-changing motors) can be increased in a ratio of 1: 2 and thus its speed can be changed approximately in a ratio of 2: 1. Typical applications are:

  • Lathes with two basic speeds: slow or fast running.
  • 2-stage fan drive for building ventilation

With asynchronous machines in squirrel cage design, the Dahlander circuit offers the option of pole switching and thus speed switching. Each winding strand of the machine (e.g. UVW) is designed in two winding parts (1U-2U, 1V-2V and 1W-2W). Depending on their connection in series or parallel operation, the number of poles can be switched in a ratio of 2: 1. The rotating field speed changes accordingly. The most common is the triangle-double star connection. When the winding parts are connected in series, the strands are triangularly linked, while the winding parts connected in parallel are star-linked in order to avoid excessive magnetic flux density in the useful area of ​​the stator by reducing the voltage of the winding part.

As with synchronous machines, increasing the speed above the speed specified by the mains frequency for "single-pole" three-phase machines is only possible by increasing the frequency (e.g. by using a frequency converter ) or by using gears .

Fans or fans often have a large moment of inertia ( moment of inertia ) when they reach the high operating speed . This makes switching from high speed to low speed a mechanical problem. The shaft or the coupling can be destroyed by the sudden change in speed. A coasting time must therefore be taken into account so that the current speed is below the nominal speed.

Pole-changing motors can also be used in asynchronous generators with squirrel cage rotors. The pole-changing windings result in a smoother network coupling and an optimal energy yield over the entire power range. A variation by Gordon Hindle Rawcliffe is the so-called PAM circuit. It enables a speed ratio of 1: 1.5 as a 4/6 pole drive based on the Dahlander principle.

literature

  • Theodor Schmelcher: Handbook of Low Voltage, project planning information for switchgear, switchgear and distribution boards. 1st edition, Siemens Aktiengesellschaft (Abt. Verlag), Berlin and Munich, 1982, ISBN 3-8009-1358-5
  • Günter Boy, Horst Flachmann, Otto Mai: The master's examination in electrical machines and control technology. 4th edition, Vogel Buchverlag, Würzburg, 1983, ISBN 3-8023-0725-9

Individual evidence

  1. ^ Kurt Jäger, Friedrich Heilbronner: Lexicon of electrical engineers . 2nd Edition. VDE-Verlag, 2010, ISBN 978-3-8007-2903-6 , p. 93 .

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