Unbalanced Operation of Six Phase Slip Ring Induction Motor-Rotor with Two Phases Open

B. Brahmaiah, P.S. Subramanyam (India), and K. V. Babu (USA)


DTPT(Dual Three phaseTransformation), Six-Phase Induction Motor, Unifiedtheory of Electrical machines, Unbalanced operation, Sequence network.


The analysis of the performance of the six-phase Induction motor under unbalanced conditions of operation forms an interesting application of the methods of unified theory of Electrical machines. The unbalanced operation of six phase Induction motor is considered when the stator windings are connected to a balanced six phase supply in the normal manner but two of the six phases of the wound rotor are open. This may arise in practice due to a broken connection or wear & tear of the brushes. The analysis is done in terms of the familiar three phase symmetrical components using Dual Three Phase Transformation (DTPT) method wherein the six phase system is treated as two mutually coupled three phase systems. The response of the six-phase Induction motor to these sequence voltages is quite independent. Torque is calculated which is the sum of positive sequence torque and negative sequence toque. When the rotor two- phases are open the torque obtained is above 67% of normal total torque when the six-phase rotor is short-circuited. The equivalent circuit is drawn from the sequence equations obtained. Torque is also calculated from the equivalent circuit. Both results agree with each other.

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