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Operating Principle of Three Phase AC Commutator Motors

By Cayla | Published on Nov 02,2015
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Three-phase AC commutator motor is a three-phase AC motor with a commutator (see DC motor) of the armature windings on a rotor. Also known as the three-phase asynchronous commutator motor or rectified AC small motors. It is a constant torque AC variable speed motor.

Principle: rotor winding with slip ring going through a three-phase AC motor for generating an air gap magnetic field, it is relative to the rotor rotating at the same speed пs. If the rotor itself rotates at speed п in the opposite direction, the magnetic field relative to the speed of stator windings and each branch commutator is the slip speed (пs-п), whereby electromotive force induced by the stator windings and commutator winding is the slip frequency. It changes over the slip (see asynchronous motor) . However, the magnetic field has a fixed relative speed (synchronous speed пs) for the rotor , it has nothing to do with the size of the electric force of commutator winding and slip.

Its speed range is wide. The ratio of the maximum speed and minimum speed is usually 3: 1,6: 1,10: 1. It also has the function of regulating the power factor, so that the maximum rated speed at full load power factor is up to 0.98 when there is in the absence of compensation. Compared with the general three-phase cage induction motor, the starting current of three-phase AC commutator motor is small, the starting torque is larger, but full-load efficiency is less; Compared with electromagnetic speed asynchronous motor, it not only can change speed under overload conditions, the speed range is wider, its performance is similar with thyristor motor. Therefore, the three-phase AC commutator motors are suitable for textiles, paper, sugar, rubber and others taht requires smooth speed change at a wide range.

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