Electrical Engineering ⇒ Topic : Uses and Speed-torque characteristics of reluctance motor
Uses. Despite its short-comings, the reluctance motor is widely used for many constant speed applications such as recording instruments, time devices, control apparatus, regulators, and phonograph turntables.Reversing is obtained as in any single-phase induction motor.
Speed-torque characteristics. Fig.(a), shows speed-torque characteristics of a typical single-phase reluctance motor .The motor starts at anywhere from 300 to 400 per cent of its full-load torque (depending on the rotor position of the unsymmetrical rotor with respect to the field windings) as a two-phase motor as a result of the magnetic rotating field created by a starting and running winding (displaced) 90° in both space and time.At about 3/4th of the synchronous speed, a centrifugal switch opens the starting winding, and the motor continues to develop a single-phase torque produced by its running winding only.As it approaches synchronous speed, the reluctance torque (developed as a synchronous motor) is sufficient to pull the rotor into synchronism with the pulsating single-phase field.The motor operates at a constant speed up to a little over 200% of its full-load torque. If it is loaded beyond the value of a pull-out torque, it will continue to operate as a single-phase induction motor up to 500% of its rated output.
Fig.(a). Speed-torque characteristics of a single-phase reluctance motor.
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