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As a prime driver, induction motor is the most electric energy consuming component in industry. The exposure of the motor to stator winding asymmetry, combined with broken rotor bar fault significantly increases the temperature and reduces the efficiency and life of the motor. Accurate and timely diagnosis of these faults will help to maintain motors operating under optimal status and avoid excessive energy consumption and severe damages to systems. This paper examines the performance of diagnosing the effect of asymmetry stator winding on broken rotor bar (BRB) faults under closed loop operation modes. It examines the effectiveness of conventional diagnostic features in both motor current and voltage signals using spectrum and modulation signal bispectrum analysis (MSBA). Evaluation results show that the combined faults cause an additional increase in the sideband amplitude and this increase in sideband can be observed in both the current and voltage signals under the sensorless control mode. MSB analysis has a good noise reduction capability and produces a more accurate and reliable diagnosis in that it gives a more correct indication of the fault severity and its location for all operating conditions. ARTICLE HISTORY

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Journal bearings are widely used to undertake a wide range of operating conditions. Under high radial load, low rotating speed and thin lubrication films, asperity collisions between the journal and the bearing surfaces may occur. These self-excitations can create wideband random vibrations due to asperity contact and asperity churn. On the other hand, under low radial load and high rotating speed they can have instable operations due to oil whirls and shaft fluctuations. In addition, because of high lubricant viscosity, fluid shearing forces can be dominant, which may also result in wideband vibrations. These types of excitations together with structural responses can be coupled to produce nonlinear modulation phenomena. In this paper, modulation signal bispectrum (MSB) is used to analyses the vibration responses in order to identify the vibration signals values under different operating conditions and hence achieve condition monitoring of journal bearings. Furthermore, MSB coherences display clear regular modulating components in the high carrying frequency range due to coupling between shaft frequencies and the wideband compounds. In associating MSB-Coh. with normalising of MSB magnitude makes possibility to differentiate responses between asperity collision vibration and instability vibration. Thereby, it is possible to identify optimal operating conditions and detect abnormal operations caused by degraded lubrications or worn surfaces.

Abstract-As a primer driver, induction motors are the most electric energy consuming component in industry. The exposure of the motor to stator winding asymmetry, combined with broken rotor bar fault significantly increases the temperature and reduces the efficiency and life of the motor. Accurate and timely diagnosis of these faults will help to maintain motors operating under optimal statues and avoid excessive energy consumption and severe damage to systems. This paper examines the performance of diagnosing the effect of asymmetry stator winding on broken rotor bar faults under closed loop operation modes. It examines the effectiveness of conventional diagnosis features in both motor current and voltage signals using spectrum and modulation signal bispectrum analysis (MSBA). Evaluation results show that the combined faults cause an additional increase in the sideband amplitude and this increase in sideband can be observed in both the current and voltage signals under the sensorless control mode. MSB analysis has a good noise reduction capability and produces a more accurate and reliable diagnosis in that it gives more correct indication of the fault severity and location for all operating conditions. Keywords-Induction motor; stator winding asymmetry and broken rotor bar faults; Variable speed drive; Motor current and voltage signatures analysis.