Faults In Squirrel Cage Induction Motors Research Articles

Mathematical modelling of induction motors taking into account design-parameter asymmetry

Due to their numerous technical and economic advantages, induction machines (IM) with squirrel-cage rotors are important components of many industrial processes. Their reliability, durability, and ease of operation make them indispensable in various industries, ensuring stable and efficient equipment performance. However, to minimise the risk of costly production failures caused by sudden stoppages, it is important to implement effective diagnostic and monitoring methods. The most common type of fault in squirrel-cage induction motors is the breakage of cage bars and end ring segments, particularly in motors with high inertia loads and frequent stops and starts. Regular maintenance and the implementation of modern control systems in the industry will help ensure the reliable and uninterrupted operation of these machines. In the technical literature, various diagnostic methods have been proposed. Some are based on analysing data collected from the induction motor (IM), detecting characteristic perturbations that indicate faults in the machine. Other methods involve comparing the data obtained from the actual induction motor with its digital model. It is clear that accurate and adequate IM models are necessary for the development and optimisation of fault diagnosis methods. This paper focuses on developing a mathematical model of an induction motor (IM) in a stator-fixed coordinate system, where the squirrel-cage rotor of the IM is represented as a multiphase, symmetrically distributed winding system in space. The adequacy of the obtained model is demonstrated. The developed model allows for the analysis of various types of asymmetries in both stator and rotor of squirrel-cage induction motors

Mixed Eccentricity Fault Detection for Induction Motors Based on Time Synchronous Averaging of Vibration Signals

This paper presents a method based on vibration signals to diagnose rotor mixed eccentricity faults in three-phase squirrel cage induction motors (SCIMs). Rotor eccentricity is a typical fault in SCIMs that significantly affects the performance of electrical machines and results in unwanted vibrations. The time synchronous averaging (TSA) signal, which consists of the harmonics components generated by the fault, is obtained via the characteristic frequency of the eccentricity fault. TSA is decomposed into two signals: TSA-regular and TSA-difference, which are respectively similar to approximate and details of wavelet transform. Based on the fault index, which is the maximum FFT value of the TSA-difference signal, the healthy and faulty motors can be distinguished. The proposed approach is evaluated on an experimental test rig equipped with a 1.5 kW SCIM supplied directly from the power grid under various load conditions. The results illustrate the effectiveness of the proposed approach in detecting the rotor mixed eccentricity faults.

Model‐based unified technique for identifying severities of stator inter‐turn and rotor broken bar faults in SCIMs

Condition monitoring is an essential technology for detecting various incipient defects in electrical machines. Stator inter-turn and rotor broken bar faults are two major faults of the squirrel cage induction motors (SCIMs). Many attempts have been made to provide fault diagnosis systems for detecting the faults individually. This study proposes a novel unified fault diagnosis system for detecting the faults and identifying their exact severities. The system is based on a flexible model of the SCIM and can identify the severities of the faults even if they are presenting simultaneously. Robustness against the motor load change, the unbalance degree of the voltage supply and its distortion are the other merits of the proposed fault diagnosis system. Experimental results under various fault modes and operating conditions demonstrate the effectiveness of the proposed fault identification technique.

Problems of diagnostics of asynchronous motor powered by an autonomous voltage inverter

The article considers the most modern and most informative methods for diagnosing faults in squirrel-cage induction motors with a short-circuited rotor. The methods are based on the evaluation of vibrations and electrical parameters, as well as coordinates during operation and are normalized when powered from a sinusoidal voltage with frequency of 50 Hz. The main advantages and disadvantages of these methods, as well as the main indicators characterizing the general technical condition of the electric motor, are described. The application of these methods when powered from a non-sinusoidal voltage is impossible due to the complex harmonic composition of current and voltage. The consequence of this composition are the ripple moment and additional power loss. The interaction of the harmonics of the inverter and subharmonics, caused by faults, leads to the occurrence of a resonance phenomenon, and therefore to a decrease in the stability of the electric drive.

Influences on the electromagnetic torque and rotor force of different faults in squirrel-cage induction motors

Based on the scalar 3D formulation and the step by step in time domain finite element solution of the electromagnetic field in a squirrel-cage induction motor, the time dependence and harmonics of the electromagnetic torque and rotor unbalanced force are computed. The results for different faulty states of motor operation are compared with those for the healthy motor. In comparison with the healthy state, when the imposed speed motion model for loaded motor operation is considered, only the broken bar fault has a consistent influence on the mean value of the motor torque. Important influences on the mean values of the rotor unbalanced force are in decreased order the broken bar fault, the rotor eccentricity fault and the stator short-circuit fault. All the three faults generate specific harmonics of the motor torque and of the rotor force.

A Simplified Frequency-Domain Detection of Stator Turn Fault in Squirrel-Cage Induction Motors Using an Observer Coil Technique

This paper presents the distinct advantages of stator fault detection using a novel radial flux sensing technique. Intensive research efforts in the past have been focused on the flux signature analysis as they have been more efficient compared to classical motor current signature analysis. In this paper, it is observed that a flux sensing simple internal observer coil (OC) is more succinct than external flux sensors. The proposed simplified, inexpensive technique has yet not been reported in the literature. The new results of root mean square (RMS), fundamental, third harmonic, and total harmonic distortion analysis of the voltage spectra of the OCs are found to exhibit variations in relation to the severity of interturn faults as compared to the healthy condition. The mathematical theory of the technique is provided and supported by an experimental validation. An experiment for confirming the performance of the proposed method was done on a 2.2-kW three-phase four-poles, 440-V squirrel-cage induction motor, increasing the fault level in steps from 1% to 15% combined with variations in load from no load to full load.

Off-the-Grid Compressive Sensing for Broken-Rotor-Bar Fault Detection in Squirrel-Cage Induction Motors

In this paper, we propose an off-the-grid compressive sensing based method to detect broken-bar fault in squirrel-cage induction motors. To validate our method, we first build a dynamic model of squirrel-cage induction motor using multi-loop equivalent circuit to simulate motor current under fault conditions. We then develop an off-the-grid compressive sensing algorithm to extract the fault characteristic frequency from the simulated motor current by solving an atomic norm minimization problem. Comparing to other fault detection methods via motor current signature analysis, our method yields high resolution in extracting low-magnitude fault characteristic frequency with only 0.7 second measurements. Simulation results validate our proposed method.

Detection of Induction Motor Faults in Inverter Drives Using Inverter Input Current Analysis

Broken rotor bar/end-ring and eccentricity are common faults in squirrel-cage induction motors and have been thoroughly investigated in the case of ac grid supply. In this paper, these types of faults are studied in the case of inverter-driven motors. More specifically, a novel investigation in inverter input current spectrum is made in order to reliably detect the fault-indicative frequency components. These harmonics give the ability for fault detection and classification, even under low load and low motor severity fault condition in steady-state or transient operation. The proposed diagnostic method has been particularly designed for open-loop controlled variable frequency induction motor drives, which is a usual case in low-cost industrial drives where precise speed control of the motor is not required. Moreover, an alternative technique is also presented in case the stator current is measured.

Experimental Investigation on the Effects of Direct Torque Control Strategy in Eccentricity-related Frequency Components of Line Current of Induction Motors

Eccentricity is a major fault in squirrel-cage induction motors. If this fault is not diagnosed and removed in the initial stages, the rotor may rub the stator and seriously damage the motor. The most well-known and probably most applicable fault diagnosis indices are harmonics components with definite frequencies in the stator current. The main objective of this article is to investigate how a direct torque control strategy applied to induction motor affects these harmonics. Due to the non-linear nature of hysteresis controllers within direct torque control, performing an analytic study on the subject is very complicated. Therefore, an experimental approach is adopted here. An experimental setup has been provided to test the induction motor and to sample and store its line currents, while its load can be adjusted and made eccentric with various types and degrees. Also, the motor is supplied directly from mains, from an industrial drive in direct torque control mode, and from the drive in constant volts/frequency mode. The motor was tested in various eccentricity conditions, load levels, supplying manners, and speeds, and the relevant harmonics amplitudes of the line current were calculated using fast Fourier transform. Analysis for three supplying manners indicates considerable changes in the amplitudes of the proposed harmonics.

Effects of Load Magnitude on Diagnosing Broken Bar Faults in Induction Motors Using the Pendulous Oscillation of the Rotor Magnetic Field Orientation

The effects of load level on the ability to diagnose broken bar faults in squirrel-cage induction motors are studied in this paper. The pendulous oscillation of the rotor magnetic field orientation is implemented as a fault signature for rotor fault diagnostic purposes at steady-state operations. Moreover, the effects of load level on the low-side band component of the stator current spectrum, and associated diagnostic difficulties in this approach particularly in the presence of motor operation from pulsewidth-modulation drives, are reported as well. These investigations were performed through testing 2-hp and 5-hp induction motors over a wide range of load levels and control drives. The results of these tests and investigations demonstrate the efficacy of the pendulous oscillation signature as a diagnostic means that can be used for a wide range of motor operating conditions.