Pole-changing electric motors with separate windings

Two-speed asynchronous motors can be operated by installing two separate windings in the stator. By changing the pole position, one winding is switched on and the other simultaneously switched off. To prevent current from flowing through the induction winding in the switched-off winding, it must be disconnected. Motors with separate windings can also be configured for star-delta starting. This requires a terminal block with 12 terminals. When switching, the delta connection of the switched-off winding must be opened.

Pole-changing motor with different speeds

The Dahlander connection offers pole switching and thus speed switching capabilities for squirrel-cage induction motors. Each winding of the machine (e.g., UVW) is configured in two winding sections (1U–2U, 1V–2V, and 1W–2W). Depending on whether these sections are connected in series or parallel, the number of poles can be switched in a 2:1 ratio. The rotating field speed changes accordingly. The most common configuration is the delta-double-star connection. When the winding sections are connected in series, they are connected in a delta configuration, while the parallel winding sections are connected in a star configuration.

Constant and quadratic torque

Pole-changing motors are drives with a constant, quadratically increasing counter-torque. These AC motors can be designed for a rated voltage of, for example, 230 V, 400 V, or 660 V and are generally designed for direct starting via pole sequence. 60 Hz versions and IEC 38 special voltages are also available. Pole changing is achieved by:
– two separate windings in the stator, e.g. 6- to 4-pole
– a winding in Dahlander connection, e.g. 8–4 pole
– two separate windings, one of which is a Dahlander connection, e.g. 8-6-4 pole
– two separate windings, both in Dahlander configuration, e.g. 12-8-6-4-pole

Modifications to the drives

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