Broken Rotor Bar Fault Research Articles

A Reconfigurable Motor for Experimental Emulation of Stator Winding Interturn and Broken Bar Faults in Polyphase Induction Machines

The benefits and drawbacks of a 5-hp reconfigurable induction motor, which was designed for experimental emulation of stator winding interturn and broken rotor bar faults, are presented in this paper. It was perceived that this motor had the potential of quick and easy reconfiguration to produce the desired stator and rotor faults in a variety of different fault combinations. Hence, this motor was anticipated to make a useful test bed for evaluation of the efficacy of existing and new motor fault diagnostics techniques and not the study of insulation failure mechanisms. Accordingly, it was anticipated that this reconfigurable motor would eliminate the need to permanently destroy machine components such as stator windings or rotor bars when acquiring data from a faulty machine for fault diagnostic purposes. Experimental results under healthy and various faulty conditions are presented in this paper, including issues associated with rotor bar-end ring contact resistances that showed the drawbacks of this motor in so far as emulation of rotor bar breakages. However, emulation of stator-turn fault scenarios was successfully accomplished.

Low Order PWM Inverter Harmonics Contributions to the Inverter-Fed Induction Machine Fault Diagnosis

In this paper, the effects of inverter harmonics on motor current fault signatures are studied in detail. It is theoretically and experimentally shown that the fault signatures caused by the inverter harmonics are similar and comparable to those generated by the fundamental harmonic on the line current. Theoretically-derived extended relations including bearing fault, eccentricity, and broken rotor bar relations are found to match experimental results. Furthermore, it is observed and reported that the asymmetries on the rotor caused by broken rotor bars increase the amplitude of even harmonics. To confirm these claims, bearing, eccentricity, and broken rotor bar faults are tested and the line current spectrum of each faulty motor is compared with the healthy one. The proposed additional fault data are expected to contribute positively to the inverter-fed motor fault decision making algorithms.

Signature Analysis of Electrical and Mechanical Signals for Diagnosis of Broken Rotor Bars in an Induction Motor

In this paper, diagnosis of broken rotor bar faults in induction motors is presented using a time-stepping, finite element (TSFE) technique. Stator current, magnetic flux distribution, magnetic potential vector, magnetic flux density, torque, and speed of the healthy motor and motor with broken rotor bars are calculated. By analyzing the current spectrum, torque, and speed and also by precise analysis of the air gap magnetic field, the occurrence and extent of the broken rotor bars, unbalanced stator current, noise, vibration, and pulsation torque in a faulty induction motor are investigated. In previous publications on the fault diagnosis of induction motors, only one of the above-mentioned signals was used for diagnosis. However, here precise computation and analysis of the field, current, torque, speed, and their relationship and interaction in the analysis and diagnosis of the broken rotor bars are considered.

A High-Resolution Frequency Estimation Method for Three-Phase Induction Machine Fault Detection

Fault detection in alternating-current electrical machines that is based on frequency analysis of stator current has been the interest of many researchers. Several frequency estimation techniques have been developed and are used to help the induction machine fault detection and diagnosis. This paper presents a technique to improve the fault detection technique by using the classical multiple signal classification (MUSIC) method. This method is a powerful tool that extracts meaningful frequencies from the signal, and it has been widely used in different areas, which include electrical machines. In the proposed application, the fault sensitive frequencies have to be found in the stator current signature. They are numerous in a given frequency range, and they are affected by the signal-to-noise ratio. Then, the MUSIC method takes a long computation time to find many frequencies by increasing the dimension of the autocorrelation matrix. To solve this problem, an algorithm that is based on zooming in a specific frequency range is proposed with MUSIC in order to improve the performances of frequency extraction. Moreover, the method is integrated as a part of MUSIC to estimate the frequency signal dimension order based on classification of autocorrelation matrix eigenvalues. The proposed algorithm has been applied to detect a rotor broken bar fault in a three-phase squirrel-cage induction machine under different loads and in steady-state condition.

Rotor broken bar fault diagnosis for induction motors based on double PQ transformation

A new rotor broken bar fault diagnosis method for induction motors based on the double PQ transformation is presented. By distinguishing the different patterns of the PQ components in the PQ plane, the rotor broken bar fault can be detected. The magnitude of power component directly resulted from rotor fault is used as the fault indicator and the distance between the point of no-load condition and the center of the ellipse as its normalization value. Based on these, the fault severity factor which is completely independent of the inertia and load level is defined. Moreover, a method to reliably discriminate between rotor faults and periodic load fluctuation is presented. Experimental results from a 4 kW induction motor demonstrated the validity of the proposed method.

Induction motor rotor fault diagnosis method based on double PQ transformation

This paper presents a new rotor fault diagnosis method for induction motors which is based on the double PQ transformation. We construct the PQ transformation matrix with the positive sequence fundamental voltage components and their Hilbert transformation as elements. The active power P and the reactive power Q are obtained through the PQ transformation of the stator currents. As both P and Q are constant for a healthy motor, they are represented by a dot on the PQ plane. Whereas the P and Q for a rotor broken bar motor are represented by an ellipse because they comprise an additional frequency component 2sf s (s is the slip and f s is the supply frequency). Thus, by distinguishing these two different patterns, the rotor broken bar fault is detected. We use the major radius of the ellipse as the fault indicator and the distance between the point of no-load condition and the center of the ellipse on the PQ plane as its normalization value. We thus arrive at the fault severity factor which is fairly independent of the load level and the inertia value of the induction motors. Experimental results have demonstrated that the proposed method is effective in identifying the rotor-broken-bars fault and at determining the severity of the fault.

Rotor broken-bar fault diagnosis of induction motor based on HHT of the startup electromagnetic torque

This paper presents a new method for rotor broken-bar fault diagnosis of induction motors. The asymmetry of the rotor caused by broken-bar fault will give rise to the appearance of additional frequency component of 2sf s (s is slip and f s is supply frequency) in the electromagnetic torque spectrum. The startup electromagnetic torque signal is decomposed into several intrinsic mode function (IMF) with empirical mode decomposition (EMD) based on the Hilbert-Huang Transform. Then, using the instantaneous frequency extraction principle of the Hilbert Transform, the rotor broken-bar fault characteristic frequency of 2sf s can be exactly extracted from the IMF component, which includes the rotor fault information. Moreover, the magnitude of the IMF which includes the rotor fault information can also give the number of rotor broken bars. Experimental results demonstrate that the proposed electromagnetic torque-based fault diagnosis method is feasible.

MIXED FAULT DIAGNOSIS IN THREE-PHASE SQUIRREL-CAGE INDUCTION MOTOR USING ANALYSIS OF AIR-GAP MAGNETIC FIELD

In this paper fault diagnosis of induction motor under mixed fault is carried out using precise analysis of the air-gap magnetic field based on time stepping finite element method. By feeding voltage instead of current density to the finite element computation part, the drawbacks of the application of finite element method in fault diagnosis of induction motor are overcome. Normally static eccentricity and broken rotor bars faults have been individually diagnosed in the published papers. Here diagnosis of the mixed fault,including static eccentricity and broken rotor bars,is introduced which is considered as a novel part of the present work. Precise analysis of magnetic field in the air-gap of a faulty induction motor is carried and performance of the motor is predicted. Taking into account the magnetic core saturation is another advantage of the present work. This is required in the transient analysis of a faulty motor.

A validated model for the prediction of rotor bar failure in squirrel-cage motors using instantaneous angular speed

Instantaneous angular speed (IAS)-based condition monitoring is an area in which significant progress has been achieved over the recent years. This condition monitoring technique is less known compared to the existing conventional methods. This paper presents model-predicted simulation and experimental results of broken rotor bar faults in a three-phase induction motor using IAS variations. The simulation was performed under normal, and a broken rotor bar fault. The present paper evaluates through simulating and measuring the IAS of an induction motor at broken rotor bar faults in both time and frequency domains. Experimental results show a good agreement with the model-predicted simulation results. Three vital key features were extracted from the angular speed variations. One feature is the modulating contour of pole pass frequency periods in time domain. The other two features are in frequency domain. The primary feature is the presence of the pole pass frequency component at the low-frequency region of the IAS spectrum. The secondary feature which are the multiple of pole pass frequency sideband components around the rotor speed frequency component. Experimental results confirm the validity of the simulation results for the proposed method. The IAS has demonstrated more sensitivity than current signature analysis in detecting the fault. This research also shows the power of angular speed features as a useful tool to detect broken rotor bar deteriorations using any economical transducer such as low-resolution rotary shaft encoders; which may well be already installed for process control purposes.

Induction Machine Broken-Bar Fault Diagnosis Using the Rotor Magnetic Field Space-Vector Orientation

A new technique based on rotor magnetic field space vector orientation is presented to diagnose broken-bar faults in induction machines operating at steady state. In this technique, stator currents and voltages are used as inputs to compute and subsequently observe the rotor magnetic field orientation, which has a more significant swing-like in case of broken-bar faults than in healthy operation. It will be shown here that the range of this pendulous oscillation is a function of the number of broken bars. Also in this technique, it was found that an inter-turn shorted stator-winding fault, which exhibits similar oscillation, could be distinguished from rotor broken-bar faults through the use of a variance index. In order to validate this method, experimental evidence is given here for several broken-bar cases in a 2-hp three-phase two-pole squirrel-cage induction machine.

Broken bar detection in induction motors using current and flux spectral analysis

Spectrum analysis of the stator current is commonly used for detecting broken rotor bar faults in induction motors. In this paper we examine the practicality of estimating the number of broken bars using stator current and axial leakage flux measurements. The work is based on experimental current and flux measurements taken from induction motors as the number of broken rotor bars is progressively increased. The test results are compared with theoretical predictions and empirical results from other researchers. The effect of partial load operation is also examined.