Analysis of Three-Phase Induction Motor with Faulty Cage Rotor Ikuro Morita, Member

Abstract

The rotor bars and end-rings of a squirrel cage induction motor are forced to break when it is driven under the overload duty cycle as frequently accelerating and braking operations, although it has essentially mechanical ruggedness.
In this paper we present a model of squirrel cage induction motor with the above rotor faults, show a method of analysis, and discuss the relations between the various faults conditions and the amplitude of abnormal frequency components of the currents and torque. The results are summarized as follows.
(1) The amplitude of abnormal frequency component increases with the number of broken bars, while it decreases with increasing the number of broken end-rings, in the case of less than five consecutive fault positions.
(2) The amplitude of abnormal frequency component becomes maximum when the distance between two broken bars is 180°k(k=l, 2, …, 2P-1: P; No. of pole pairs) in electrical angle, whereas it becomes minimum at 90°×(2k-1) (k=1, 2, …, 2P) in angle.
(3) The influence of end-ring faults is maximum at 180°×(2k-1) (k=1, 2, …, 2P) in electrical angle.
It is assured that the measured results obtained by the artificially faulted test machine have a good agreement with the analytical results.