hysteresis motor

hysteresis motor [‚his·tə′rē·səs ¦mōd·ər]

(electricity)

A synchronous motor without salient poles and without direct-current excitation which utilizes the hysteresis and eddy-current losses induced in its hardened-steel rotor to produce rotor torque.

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Hysteresis motor

A type of synchronous motor in which the rotor consists of a central nonmagnetic core upon which are mounted rings of magnetically hard material. The rings form a thin cylindrical shell of material with a high degree of magnetic hysteresis. The cylindrical stator structure is identical to that of conventional induction or synchronous motors and is fitted with a three-phase or a single-phase winding, with an auxiliary winding and series capacitor for single-phase operation. See Induction motor, Synchronous motor

When the motor is running at synchronous speed, the hysteresis material is in a constant state of magnetization and acts as a permanent magnet. Full-speed performance is therefore exactly the same as in a permanent-magnet synchronous motor.

The outstanding special feature of a hysteresis motor is the production of nearly constant, ripple-free torque during starting. Hysteresis motors are widely used in synchronous motor applications where very smooth starting is required, such as in clocks and other timing devices and record-player turntables, where smooth starting torque reduces record slippage. Hysteresis motors are limited to small size by the difficulty of controlling rotor losses caused by imperfections in the stator mmf wave. See Alternating-current motor, Motor