Electric motor for operation on a single-phase AC network.
The rotor winding is designed as a squirrel cage, whereas the stator winding usually consists of two phases (main and auxiliary phase). The magnetic axes of the stator winding are arranged offset by half a pole pitch, i. e. 90 ° electrically, with respect to each other. The auxiliary phase is used to generate a rotating field component in the gap of the machine to allow an automatic motor start. For this, the auxiliary phase is temporarily supplied via a resistor or a starting capacitor when the motor is switched on.
With motors equipped with an operating capacitor (capacitor motors), the auxiliary phase also remains switched on during operation.
A large number of single-phase asynchronous motors are used in low-power drives below 1 kW.
For extremely low powers up to approx. 150 W, single-phase asynchronous motors are available as shaded-pole motors. These motors are usually equipped with a stator with salient poles including one or several shading coils that perform the function of the auxiliary phase.
All single-phase asynchronous motors show a typical shunt behaviour, i.e. their speed slightly decreases with increasing load. If the load torque exceeds the stall torque, they will stop.
