End-ring Faults Research Articles

Diagnosis of rotor faults by fast Fourier transform using an auxiliary winding voltage

<p>Condition monitoring and on-line detection have attracted several researchers in order to carry out an efficient diagnosis of machine failures. Therefore, the detection in early stage avoids system breakdown and reduce the maintenance cost. This paper presents a new diagnosic approach to detect the broken bars and broken end ring faults for a squirrel cage induction machine based on the fast Fourier transform analysis applied on a new signature as the voltage of an auxiliary winding. The auxiliary winding is a small coil inserted between two of the stator phases, the explicit expression of its voltage is presented. The signal is monitored in six faults cases under a different load level, the emergence of the fault frequencies changes for each kind of failure. The successfully simulation results obtained show the effectiveness of this approach.</p>

Effects of induction motor end ring faults on motor performance. Experimental results

Abstract Induction motors are inherently robust in construction, although faults can occur inside or outside in the motor due to various reasons. These failures cause deterioration of the motor performance and it can even cause the motor to be disabled. As a result of literature studies, it has been seen that a hole is opened in the middle part of the rotor bars for the induction motor rotor bar failures. In this study, different the studies in the literature, faults were introduced on the end ring part and on the intersections of the end ring and the rotor bars. The aim of this paper, end ring faults was investigated the effect of a squirrel cage induction motor on the motor performance. Seven motors with the same power and physical characteristics were used in the study. One of the motors is used as a reference (healthy) motor and the other six motors which have got with various faults in the end ring part. The three motors were used exactly as the faulty motor at the intersection of the end ring and the rotor bars, and the other three as the faulty motor which caused a scraped on the end ring part. No-load, locked-rotor and loaded operation tests were performed separately for each motor. The core losses, copper losses, current, power factor, efficiency, torque-speed characteristic and etc. values were obtained for seven motors. The motors that are tested are squirrel cage, 3 phase and 4 kW power. The obtained results are presented in comparative tables and graphs. Core loss and copper losses have increased by 21.57% for 3 scrapped motor and 9.83% for 2 broken rotor bar motor respectively, compared to the healthy motor. The efficiency value is reduced by 3.4% for the 3 scraped motor.

Broken bar and end-ring faults: analysis of their effects on the rotor cage currents

Purpose – The purpose of this paper is to investigate the effects of different faulty scenarios on the induction motor (IM) operation with emphasis on the currents in the rotor bar and end rings. Design/methodology/approach – The modeling of the IM followed by a graphical representation-based analysis of the rotor steady-state currents under healthy operation is treated. Then, a case study is considered in order to investigate different faulty scenarios with a focus on the rotor cage currents. Findings – It has been found that the rotor faults greatly affect the currents in the bars and in the end rings both in amplitude and in harmonic content. These vary according to the relative positions with respect to the fault such that: the currents in the bars adjacent to the faulty one(s) have the highest amplitudes with the lowest harmonic content; and the ones in the ring portions adjacent to the faulty one have the lowest amplitudes with the highest harmonic content. Research limitations/implications – Although the simulated model has confirmed the well known IM behavior under healthy operation, it would be appreciated if the obtained results under faulty operation would be validated by finite element analysis. Practical implications – It is of great interest to investigate the effects of faulty scenarios on the rotor cage currents, in order to take appropriate actions starting from the design of the IM. Originality/value – A deep investigation (including the waveforms, the phasor diagrams and the harmonic content) of the effects of different faulty scenarios on the IM rotor cage currents represents the major contribution of this work.

Analysis and Failure Diagnosis of Squirrel-Cage Induction Motor with Broken Rotor Bars and End Rings

This study investigates the diagnosis of not only broken bar but also broken end ring faults in an induction motor. The difference between the broken bars and broken end ring segments is experimentally clarified by Fourier analysis of the stator current. This difference is verified by two-dimensional finite element (FE) analysis that takes into consideration the voltage equation and the end ring. The electromagnetic field in the undamaged motor and the motor with broken bars and broken end rings is analyzed. Moreover, the effect of the number of broken bars and broken end ring segments on the motor performance is clarified.

Oxidation Models of Rotor Bar and End Ring Segment to Simulate Induction Motor Faults in Progress

Oxidation models of a rotor bar and end ring segment in an induction motor are presented to simulate the behavior of an induction machine working with oxidized rotor parts which are modeled as rotor faults in progress. The leakage inductance and resistance of the rotor parts are different from normal values because of the oxidation process. The impedance variations modify the current density and magnetic flux which pass through the oxidized parts. Consequently, it causes the rotor asymmetry which induces abnormal harmonics in the stator current spectra of the faulty machine. The leakage inductances of the oxidation models are derived by the Ampere’s law. Using the proposed oxidation models, the rotor bar and end ring faults in progress can be modeled and simulated with the motor current signature analysis (MCSA). In addition, the oxidation process of the rotor bar and end ring segment can motivate the rotor asymmetry, which is induced by electromagnetic imbalances, and it is one of the major motor faults. Results of simulations and experiments are compared to each other to verify the accuracy of the proposed models. Experiments are achieved using 3.7 ㎾, 3-phase, and squirrel cage induction motors with a motor drive inverter.

Experimental study for sensorless broken bar detection in induction motors

Abstract This study presents experimental results of sensorless broken bar detection in induction motors based on fluctuations of the stator current zero crossing instants before actual breakdown occurs. These fluctuations are sensed by a microcontroller (μC), and transferred to a computer for monitoring the amplitude changes on specific frequency components using fast Fourier transformation algorithms. The motor current signal is also monitored for verification purposes. The main reasons of rotor faults are broken bars, end ring faults and bearing faults. Most recent efforts are focusing on current spectrum analysis, as the current signal is easily accessible for all induction motors. Instead of sampling motor current with a high resolution analog to digital converter, zero crossing instants are recorded as the waveforms cross zero. Fluctuations in the intervals between successive zero crossings of the three phase current waveforms are analyzed in the frequency domain. Broken bars and end ring breakages, supply unbalances, rotor eccentricities and shaft misalignment faults are distinguished by monitoring amplitude changes of the 2 sf , f r , and 2 f spectral components, where s is the motor slip, f is supply frequency and f r is rotor speed. Appearance of only the 2 sf component in zero crossing times (ZCT) of the signal spectrum implies rotor faults. The 2 f component occurs only when supply is unbalanced or in the case of stator winding faults. Separation of these two faults is implemented by monitoring both components. In addition, when there is additional rotor eccentricity due to bearing deterioration or shaft misalignment, it is also necessary to monitor the f r fault signature component to distinguish mixed faults. It may be necessary to include additional signals such as motor vibration or temperature to extend the reliability of the fault detection system for critical machines.

A Computationally Efficient Winding Function Method for Calculation of Inductances in an Asymmetric Induction Motor

Winding function theory has been successfully applied for the calculation of magnetizing inductances of asynchronous and synchronous rotating machines for steady-state and transient analysis. The computational burden in such simulations is heavy because of the calculation of a large number of inductances of the stator and rotor circuit coils, at every time step, each of which requires evaluation of definite integrals of the products of winding functions, their distributions and inverse air gap functions around the rotor periphery. This article proposes a modified discrete space model of continuous space winding function of a squirrel cage induction motor. The discrete model uses the air gap functions directly and consequently eliminates inverse air gap functions and their approximations. Further, it uses simple and direct formulae for the calculation of motor inductances, which results in considerable reduction in the computational complexity and execution time while preserving the accuracy of computation. Discrete winding functions are suitable for the simulation of gradual changes in asymmetrical faults such as eccentricity, rotor bar faults and end ring faults in a three phase squirrel cage induction motor. Simulation results show the comparative assessment of computational complexity, accuracy and execution time required for the calculation of the stator and rotor inductance values of an asymmetrical induction motor.

Effects of Rotor Bar and End-Ring Faults Over the Signals of a Position Estimation Strategy for Induction Motors

The effect of rotor faults, such as broken bars and end-rings, over the signals of a position estimation strategy for induction motor drives is analyzed using a multiple coupled circuit model. The objective of this analysis is to establish the possibility of using the estimation strategy signals for fault diagnosis in variable-speed electric drives. This strategy is based on the effect produced by inductance variation on the zero-sequence voltage, when exciting the motor with a predefined inverter switching pattern. Experimental results illustrate the feasibility of the proposal.

Simulation and Analysis of Induction Machines With Rotor Asymmetries

The need for detection of rotor faults at an earlier stage, so that maintenance can be planned ahead, has pushed the development of monitoring methods with increasing sensitivity and noise immunity. An important issue in such effort is the modeling of the induction machine including rotor bar and end-ring faults, with a minimum of computational complexity. In this paper, a new and simpler approach for the modeling of induction machines with rotor asymmetries is employed in the simulation and analysis of an induction motor with rotor asymmetries. Simulation and finite element analysis results are presented to support the proposed approach.

Transient analysis of cage induction machines under stator, rotor bar and end ring faults

An analysis method is developed for modeling of multi phase cage induction motors with asymmetry in the stator, arising due to an interturn fault resulting in a disconnection of one or more coils making up a portion of a stator phase winding and any distribution and number of rotor bar and end-ring failures. The approach, based on the winding functions, makes no assumption as to the necessity for sinusoidal MMF and therefore include all the space harmonics in the machine. Simulation and experimental results confirm the validity of the proposed method. >

Analysis of three-phase induction motor with faulty cage rotor.

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.

Steady-state analysis of double-cage induction motors with rotor-cage faults

An analysis is developed for a double-cage induction motor with any number of cage or end-ring faults. Both common end-ring and separate end-ring designs are considered. The paper addresses, in particular, the problem of detecting faults in the outer cage when the machine is running, and identifies the response of the machine to negative sequence voltages as a possible means of doing this. Experimental results are presented for a 15 kW test motor.

The Existence of Large Inter-Bar Currents in Three Phase Squirrel Cage Motors with Rotor-Bar And/Or End-Ring Faults

An analysis is developed which describes the existence of substantial inter-bar laminar currents in large three phase squirrel cage induction motors with broken bars and/or rings. Results of experimental measurements are presented which verify the theoretical model. Also the effect of these tangential currents on the production of very large axial vibrations are shown.

The Existence of Large Inter-Bar Currents in Three Phase Squirrel Cage Motors with Rotor-Bar and/or End-Ring Faults

The Existence of Large Inter-Bar Currents in Three Phase Squirrel Cage Motors with Rotor-Bar and/or End-Ring Faults

Steady-state analysis of 3-phase cage motors with rotor-bar and end-ring faults

Steady-state analysis of 3-phase cage motors with rotor-bar and end-ring faults

Reply to the comments of Drs. Hargis and Vas on “Steady-state analysis of 3-phase cage motors with rotor-bar and end-ring faults”

Reply to the comments of Drs. Hargis and Vas on “Steady-state analysis of 3-phase cage motors with rotor-bar and end-ring faults”

Steady-state analysis of 3-phase cage motors with rotor-bar and end-ring faults

Steady-state analysis of 3-phase cage motors with rotor-bar and end-ring faults

Steady-state analysis of 3-phase cage motors with rotor-bar and end-ring faults

An analysis is developed for 3-phase induction motors with any distribution and number of rotorbar and end-ring failures. The method is verified, using an inverted-geometry cage motor on which careful measurements of rotor-bar currents are made. The analysis is then used to investigate a rotor-bar fault on a 250 hp, 8-pole, 60 Hz motor.