Diagnostics of rotor and stator problems in industrial induction motors.

Abstract

In this project, two kinds of induction motor faults, stator short circuit fault and broken rotor bar fault, are investigated by using motor current signature analysis (MCSA) and zero crossing time (ZCT) method. These methods are based on the detection of sidebands around the supply frequency in the stator current signal. The thesis starts by a review of these two common faults and two commonly used diagnostic methods. Before the motor stator short circuit faults experiments, baseline analysis is carried out on two same types of healthy motors. Meanwhile, signal processing programs, composed in MATLAB and LABVIEW, are verified to ensure the accurate diagnosis of motor faults. Through a control box, artificial turn to turn fault and phase to phase fault are structured in each test. MCSA and ZCT are utilized to extract broken rotor bar information from recorded stator current signal. Although an induction motor is highly symmetrical, it may still have a detectable signal component at the fault frequencies due to imperfect manufacture, improper motor installation and so on. The misalignment experiments reveal that improper motor installation could lead to an unexpected frequency peak, which will affect motor fault diagnosis. Furthermore, manufacture tolerance and working environment could also result in disturbing the motor fault diagnosis. Through both online and offline experiments, MCSA and ZCT methods could detect particular abnormal harmonics related to stator short circuit fault and broken rotor bar fault. Compared with the conventional MCSA method, the ZCT method has the advantage of reduced computational burden.