8.10 Induction (asynchronous) motors 8.10.1 General characteristics The function of the motor is to rotate the drum at different speeds: Ц high speed for the spin phases Ц low speed for the wash phases The primary characteristics of these motors is that they do not require a start-up current. Instead, the current in the rotor builds up by induction, hence the name "induction" motor. These motors are also termed "asynchronous" because the speed of rotation is not the same as the synchronization speed. 1. Shield 2. Bearing 3. Rotor 4. Stator The rotor is of the "squirrel cage" type, in which the die-cast aluminium windings are housed in special grooves in the plate pack.
The starting torque of single-phase asynchronous motors is very low. This is offset by adding a start-up circuit which is phase-shifted by 90° with respect to the running circuit. This 90° current phase shift is provided by a capacitor which is connected in series to the start-up winding. This generates a rotary field that is sufficient to create the starting torque. The stator consists of four windings: Ц two high-speed two-pole windings for operation during spin phases: a start-up winding and a running winding, with the capacitor connected in series. High-speed rotation of the drum is always in the same direction (counter-clockwise).
Ц two low-speed windings for operation during washing phases. These have 12 or 16 poles, and are identical in structural terms. SOI/DT 2002-05 eb 75 599 35 23-17 Type of motor Capacitor (µF) Motor speed (rpm at 50Hz) Drum rotation speed (rpm) Wash Spin Wash Spin 2/12 poles 14 ~ 400 ~ 2800 ~ 55 ~ 400 2/16 poles 16/18 ~ 300 ~ 2800 ~ 55 ~ 500/550