Three-phase Cage Induction Motor Research Articles

Influence of Electrical Circuit Parameter Changes on the Local Stability of a Three-Phase Cage Induction Motor Fed with Variable Frequency

The paper presents the mathematical support and the results of some simulations related to a new method of analyzing the stability of induction motors powered at variable frequency. After a brief introduction to the proposed issue, the mathematical model of the motor, written with relative values, is detailed. Taking this model as a starting point, a Matlab stability analysis program was created. By running this program, a series of graphs were obtained, detailed in the paper (two graphs are represented each, obtained for different conditions, which facilitate their comparison and obtaining conclusions). They refer to four specific cases regarding the modification of static inductance, rotor inductance, stator resistance and rotor resistance. Analyzing these graphs, the necessary conclusions were drawn. The conclusions are important, mainly in the design phase of the machine, to finalize the structure corresponding to the most stable operation of the drive system with asynchronous motor and static voltage and frequency converter. They highlight the influences of the most important parameters of the motor on the stability of the functioning of systems with such a structure. The paper ends with a representative bibliography for the proposed study.

Research on Influence of Eccentricity on Submersible Motor and its Solution

The working efficiency and stability of submersible motor are very important for energy utilization, and dynamic eccentricity is the main factor affecting its efficiency and fatigue life. This paper takes a 2-pole 60kW vertical three-phase cage induction motor with static eccentricity as the research object. Through finite element analysis, the mechanical structure and coordination of submersible motor shaft and spiral pump are analyzed. The influence caused by motor shaft eccentricity is regarded as external interference received by the system. The idea of auto disturbance rejection controller to eliminate this disturbance, thereby restraining the negative effects caused by motor shaft eccentricity. By using the state expansion observer of the active disturbance rejection model to estimate and compensate the internal disturbance and uncertainty of the system in real time, the rotation error of the shaft of the submersible motor is eliminated, and the motion inconsistency between the rotor of the screw pump and the shaft of the submersible motor caused by shaft eccentricity is suppressed.

Hybrid Model-Based Fuzzy Logic Diagnostic System for Stator Faults in Three-Phase Cage Induction Motors

Hybrid Model-Based Fuzzy Logic Diagnostic System for Stator Faults in Three-Phase Cage Induction Motors

Stator Current Spectral Content of Inverter-Fed Cage Rotor Induction Motor

The paper analyzes the influence of the number of rotor bars on the stator current spectral content in a three-phase cage induction motor fed by a pulse-width modulated (PWM) inverter. It is shown that each of the higher-order time harmonics in the supply voltage produces space harmonics in a rotating magnetic flux density wave, which results in induced rotor slot harmonics (RSHs) in the stator current spectrum. The conditions for the existence of these space harmonics are identical to those applying to a mains-fed motor. In other words, the number of rotor bars of a mains-fed motor yielding an RSH-free stator current spectrum produces the same stator current spectrum even in case the motor is inverter-fed. Additionally, to minimize the adverse effects of RSHs in the stator current spectrum, one must consider not only the number of rotor bars, but also its relationship with the frequency modulation ratio of the PWM inverter. Analytical predictions are presented to illustrate these results supported both by numerical simulations of the induction motor modelled through the winding function theory and experimentally taking the case a two-pole cage induction machine as a case study.

Optimal Selection of Rotor Bar Number for Minimizing Torque and Current Pulsations Due to Rotor Slot Harmonics in Three-Phase Cage Induction Motors

The paper develops a method to choose the number of rotor bars in order to eliminate rotor slot harmonics in stator current spectrum and pulsation torques that are their consequence. Mains-fed, three-phase cage induction motors with the most common number of pole pairs and number of stator slots, that result in integer slot winding, are analyzed. The analysis is based on the recently derived general rule for optimal selection of rotor bars, valid for symmetrical multiphase machine with prime number of phases and integer slot stator winding. As a tool for validation of analytically predicted results, parameterized winding function (PWF) model is used. Electromagnetic torque ripple factor is used as a measure of goodness of the number of rotor bar selection. The practical motivation of the study is an attempt to supersede the many existing rules for rotor bar number selection that, depending on the source, may be different, and provide a unified general approach to the problem. One of the main findings derived in the paper is ascertainment that increasing the number of pole pairs increases the degree of freedom in choosing the proper number of rotor bars. The same applies when the number of motor phases increases.

Comparison analysis of induction and line-start synchronous reluctance motors

The article presents research on the development of a low-cost line start synchronous reluctance motor (LSSRM) on the basis of components of a mass-produced three-phase low-power cage induction motor (IM). The aim was to obtain the best functional parameters for both the steady-state work condition and the asynchronous start-up. In the design-optimization calculations of the LSSRM, a field model of electromagnetic phenomena developed using the MagNet program was used. Laboratory tests were carried out on the designed and constructed prototype of the LSSRM, and the obtained results were compared with the results of an IM test.

Application of the Goertzel’s algorithm in the airgap mixed eccentricity fault detection

In this paper, a suitable method for the on-line detection of the airgap mixed eccentricity fault in a three-phase cage induction motor has been proposed. The method is based on a Motor Current Signature Analysis (MCSA) approach, a technique that is often used for an induction motor condition monitoring and fault diagnosis. It is based on the spectral analysis of the stator line current signal and the frequency identification of specific components, which are created as a result of motor faults. The most commonly used method for the current signal spectral analysis is based on the Fast Fourier transform (FFT). However, due to the complexity and memory demands, the FFT algorithm is not always suitable for real-time systems. Instead of the whole spectrum analysis, this paper suggests only the spectral analysis on the expected airgap fault frequencies employing the Goertzel?s algorithm to predict the magnitude of these frequency components. The method is simple and can be implemented in real-time airgap mixed eccentricity monitoring systems without much computational effort. A low-cost data acquisition system, supported by the LabView software, has been used for the hardware and software implementation of the proposed method. The method has been validated by the laboratory experiments on both the line-connected and the inverter-fed three-phase fourpole cage induction motor operated at the rated frequency and under constant load at a few different values. In addition, the results of the proposed method have been verified through the motor?s vibration signal analysis.

Sources and Characteristics of Unbalanced Magnetic Pull in Three-Phase Cage Induction Motors With Axial-Varying Rotor Eccentricity

This paper puts forward a model for assessing unbalanced magnetic pull (UMP) due to rotor eccentricity in cage induction motors that takes into account the axial variation in the eccentricity. It is tested using ten- and four-pole machines with experimental results validating the model. This paper assesses the effects of rotor differential flux, saturation, bar number, and variable-frequency operation on the UMP and highlights the key points for the generation of UMP in cage induction motors. Both dynamic and static eccentricities are studied.

Parameter identification of a cage induction motor using particle swarm optimization

The current paper presents an adaptive system identification/parameter estimation algorithm for a three-phase cage induction motor based on particle swarm optimization (PSO). The performance of the proposed algorithm is emphasized by comparing its results with those of the well-known stochastic optimization techniques of genetic algorithm (GA) and simulated annealing (SA) for the benchmark application with six unknown parameters to identify. The dynamic inertia-weighted PSO algorithm significantly outperformed the GA and SA techniques. The achievement of the presented methodology in confronting a rather complicated non-linear dynamic engineering application underlines the ability of the algorithm to be used for a range of real-world problems, and moreover justifies and motivates the development of more advanced techniques.

Analysis of self-calibrated field aligned starting (FAS) at mains connection

Field aligned starting (FAS) is a technique for starting three-phase cage induction motors on either three-phase or single-phase supply lines under varying load conditions with minimal inrush currents. The technique starts the motor independent of the mains supply with a high transient torque before connecting the spinning motor to the mains. It is imperative to the operation of FAS that the spinning motor be connected to the mains at the correct time. Incorrectly timed mains connection can result in negative transient torques with the severity to slow, or possibly stall the already started motor. As the implementation of FAS is not possible without a predictive mechanism by which the correct moment of mains connection can be found in advance, this paper proposes a simple, low cost, yet effective self-calibrating method which ensures that the timing of the mains connection is correct under all starting conditions. Critical issues vital to a successful self-calibration under transient and varying starting conditions are investigated and presented with both experimental and simulated results to show that self-calibration is an indispensable part of FAS technique.

The Impact of Circuit Variables on the Starting Performance of Field-Aligned Starting

Field-aligned starting (FAS) is a new technique for starting three-phase cage induction motors on either three- or single-phase supply lines with minimal inrush currents. FAS generates a high impulse like torque to start the motor that is independent of the mains supply, before connecting the already spinning motor to the mains supply. In contrast to conventional starting techniques, FAS imposes higher than normal/rated voltage and current conditions on the machine at starting, and as such, the transient performance of FAS operated motors is complex in nature and largely governed by a number of key circuit variables, the values of which are critical for an efficient and economical design of FAS. A detailed insight into the influence of these key parameters on transient performance during startup is essential to avoid time consuming and inefficient trial and error design methods currently utilized in FAS designs. This paper addresses this need through the investigation of both the functionality and the extent of impact of the key variables on the starting performance of FAS. A transient model is utilized, and both experimental and simulated results suggest that, for a given set of circuit components, the proper selection of variable values is critical to achieve the best possible performance at startup.

Transient Modeling and Parameter Estimation of Field Aligned Starting

Field aligned starting (FAS) is a new technique for starting three-phase cage induction motors on single-phase supply lines with minimal inrush currents. It uses a simple energy storage system to generate a very high impulsive torque by which the motor is started before being connected to the mains supply. The spinning motor can then be connected to the mains to operate in a standard Steinmetz connection without incurring high inrush currents, if the moment of mains connection is properly timed. This paper presents a transient model and an accompanying parameter estimation method through which the transient behavior of three-phase induction motors operated with FAS can be analyzed. The proposed model is based on instantaneous symmetrical components and is used to investigate a 3 kW motor started under various operating conditions. The proposed parameter estimation method and the developed transient model are both validated by experimental results.

Critical Slip of Three-phase Cage Induction Motor Supplied from Limited Power Source

The peculiarities and characteristics of a cage induction motor supplying from limited power source (mobile electric power station, diesel power plant, wind power station and etc.) change virtually in comparison with the case when motor is supplied from unlimited voltage source. The critical slip expression of the cage induction motor operating from the limited power-supply source taking into account the inner complex impedance of power-supply source and other cable parameters has been derived. It is shown that critical slip formula, when motor is supplied from a high-capacity power-supply source (the inner complex impedance is not taken into account) and through short cable (the cable impedance is not taken into account) absolutely coincides with well-known formula. The algorithm for calculations of the induction motor characteristics taking into account the parameters of the supply circuit and the suitable length and cross-section of the supply cable has been created. Ill.1, bibl. 6 (in English; summaries in English, Russian and Lithuanian).

Optimal stator slot design of inverter-fed induction motor in consideration of harmonic losses

This paper proposes optimal design method of stator slot for three-phase cage induction motor fed by six-step inverter output voltage by using proposed analysis method. The finite-element method (FEM) on one phase band stator periodic condition is coupled with harmonic equivalent circuit. Using the FEM, the stator slot is optimally designed and the result is presented. Stator core loss and copper loss including harmonic loss are reduced by the proposed optimum slot design method. The analysis result is verified by experimental measurement.

Theory and design of part-winding starting

When a three-phase cage induction motor is started on a half winding, space harmonic MMFs occur, and the machine usually fails to accelerate beyond the speed of the principal harmonic. A mathematical theory is presented in this paper which not only explains such behavior observed in the past, but also predicts whether, and at what speed, a motor will hang up or crawl on any particular arrangement of half winding. The theory also provides a basis for the design of harmonic-free half windings on which the machine will accelerate smoothly to full speed. This is illustrated by application to a 6-pole motor.

Dynamic harmonic field analysis of a cage type induction motor when magnetic slot wedges are applied

Applying magnetic slot wedges to stator slot openings is an effective means to reduce the slot ripple harmonic components in the magnetic field. To investigate the effect of the wedges in detail, this paper proposes a new harmonic field analysis method that considers the rotor movement dynamically and the harmonic components of the secondary current as induced current by a two-dimensional finite element method (2D-FEM) using a time stepping technique. The differences in harmonic characteristics due to the use of plural wedges (a nonmagnetic wedge and magnetic slot wedges in different dimensions) for the stator slot opening of a three-phase cage induction motor are evaluated using the method. Suitable wedge dimensions to reduce the slot ripple harmonics are determined. From the comparison of calculated and experimental results of secondary current, the proposed method is shown to be appropriate and useful for the quantitative estimation of harmonic fields for induction motors.

3-D electro-magnetic analyses of a cage induction motor with rotor skew

The paper studied the performance characteristics of a three-phase cage induction motor using a 3D finite element technique. Especially, the effects of rotor skew and the rotor end-rings and the distribution of the electromagnetic field toward the axial direction, which have not been able to be analyzed accurately by 2D analysis, were investigated. Since the 3D analysis enabled the analysis of the continuity of the air gap flux density at the core ends and to take into consideration the rotor end-ring impedance, the motor parameters were calculated with high accuracy, compared with 2D analysis. Firstly, the authors made the relation of the rotor end-ring current with the rotor bar current clear, by analyzing the harmonics of the rotor bar current and the rotor end-ring current in the cases of motors without rotor skew and with rotor skew. Secondly, the torque and the rotor axial force were calculated from the distribution of the electromagnetic field obtained by the 3D analysis in the case of rotor skew. They also calculated the axial forces on the both end-rings in the case of rotor skew. The results obtained in the paper show the importance of 3D analysis for the design of induction motors.

Calculation of cage induction motor equivalent circuit parameters using finite elements

A means by which the finite-element method can be used in conjunction with the conventional equivalent circuit model to determine the equivalent circuit components for a three-phase cage induction motor is described. The method uses separate finite-element models for the rotor and the stator, consisting of one slot pitch and one phase band, respectively. The use of minimal models leads to a fast execution time. The method is illustrated by comparing computer predictions of performance with test measurements made on four motors, ranging in size from 4 to 150 kW.