Three-phase Squirrel-cage Induction Research Articles

An integrated 2D/3D numerical methodology to predict the thermal field of electric motors

The present work aims at providing a predictive numerical methodology for the thermal characterization of electric motors. The methodology relies on a 2D-FE simulation for the estimation of the electromagnetic (iron and joule) losses. The latter are then exploited in a 3D-CFD Conjugate Heat Transfer analysis for the evaluation of the thermal field.The CFD model includes both the solid components and the fluid domains. The main novelty of the paper is represented by the copper coil modelling. In fact, copper, air, epoxy resin and enamel are synthetized in a single homogeneous body able to reproduce the thermal behaviour without including the single components, to reduce the computational cost.The methodology is validated against experimental data on a three-phase squirrel-cage induction motor. As for the experimental data (available at three different operating conditions), temperature distributions are measured by thermocouples at the test bench for the validation of the 3D-CFD CHT model. In addition, experimental estimations of the losses are available for the validation of the 2D electromagnetic simulations.The numerical results in terms of motor performance, electromagnetic losses and thermal field are discussed and are proved to be close to the experimental counterparts, for all the investigated conditions.

Thermal Analysis and Cooling Strategies of High-Efficiency Three-Phase Squirrel-Cage Induction Motors—A Review

In recent times, there has been an increased demand for electric vehicles. In this context, the energy management of the electric motor, which are an important constituent of electric vehicles, plays a pivotal role. A lot of research has been conducted on the optimization of heat flow through electric motors, thus reducing the wastage of energy via heat. Futuristic power sources may increasingly rely on cutting-edge innovations like energy harvesting and self-powered induction motors. In this context, effective thermal management techniques are discussed in this paper. Importance was given to the potential energy losses, hotspots, the influence of overheating on the motor efficiency, different cooling strategies, certain experimental approaches, and power control techniques. Two types of thermal analysis computation methods, namely the lumped-parameter circuit method (LPCM) and the finite element method (FEM), are discussed. Also, this paper reviews different cooling strategies. The experimental research showed that the efficiency was greater by 11% with the copper rotor compared to the aluminum rotor. Each rotor type was reviewed based on the temperature rise and efficiency at higher temperatures. The water-cooling method reduced the working temperatures by 39.49% at the end windings, 41.67% at the side windings, and by a huge margin of 56.95% at the yoke of the induction motor compared to the air-cooling method; hence, the water-cooling method is better. Lastly, modern cooling strategies are proposed to provide an effective thermal management solution for squirrel-cage induction motors.

Derating of Squirrel-Cage Induction Motors Due to High Harmonics in Supply Voltage

This paper presents the results of load capacity calculations for three-phase squirrel-cage induction motors supplied with distorted voltage with rotating harmonics. The calculations were made on the basis of a commonly used model of an induction machine. The difference from many papers is that the parameters of the equivalent circuit of each motor were precisely determined in terms of power losses in the motor. The load capacity of the motors was made dependent on the load power losses in the rotor cage. These losses were determined on the basis of short-circuit measurements of motors, made for frequencies equal to harmonic frequencies. Measurements and calculations were made for low-voltage squirrel-cage motors with rated powers of 4–65 kW and various efficiency classes. Calculations have shown that the calculated derating curves do not match the curves given in IEC 60034-17 and NEMA MG1. The differences are up to 15% for IE1 and IE2 motors and more than 50% for IE3 motors.

Modeling and Control of an Air Conditioner Powered by PV Energy and the Grid Using a DC Microgrid

This paper presents the mathematical modeling and control design procedure of the compressor motor of an air conditioner using the energy from a photovoltaic system combined with the power grid in a DC microgrid. A comprehensive model considers the interconnection of the photovoltaic cells with their associated DC/DC converter, the DC bus, the three-phase squirrel-cage induction motor with its driver, the bidirectional DC/AC converter, the output filter, and the power grid. The state-of-the-art showed that a complete mathematical model of the proposed system is unavailable. Therefore, the mathematical model of the system is compared and validated in simulation with a block diagram in the Matlab/Simulink environment. In addition, several control approaches are used in the whole system to track the maximum power point of the photovoltaic cells, obtain a soft start on the machine, control the velocity using the variable frequency drive, regulate the DC bus voltage, and manage the power flow between the DC bus and the power grid.

Load Voltage Control of a Wind Turbine-driven Three-phase Squirrel-Cage Induction Generator in an Islanded Microgrid

The intermittent nature of the wind resources and reactive power consumptions are major issues associated with squirrel cage induction generator wind power system when operated in an island microgrid mode. The resultant effect of these two issues are continuous fluctuations of load voltage which has adverse effects on electrical devices. This paper proposes a voltage regulation technique based on proportional controller and phase deposition sine pulse width modulation (PDSPWM) for the control of 5-level neutral point clamped multilevel inverter. The instantaneous voltage tracking strategy based on root mean square value of microgrid voltage was adopted to regulate and maintain the output load voltage at 400 𝑉𝑟𝑚𝑠 despite rotor fluctuations with wind speeds. The simulation was carried out in a MATLAB/SIMULINK environment and the performance of the control scheme was found to be excellent.

Derating of Squirrel-Cage Induction Motor Due to Rotating Harmonics in Power Voltage Supply

This paper presents a method for determining the load capacity of three-phase squirrel-cage induction motors supplied with a balanced distorted voltage containing rotating harmonics (1st, 5th, 7th, 11th, 13th,...). The method is based on the dependence of the motor load capacity on the load power losses in the rotor cage. The load capacity was determined based on motor short-circuit measurements made for frequencies equal to harmonic frequencies. To evaluate the load capacity, a factor with the proposed name Harmonic Losses Factor (HLF) was introduced. Its expression is a generalization of the well-known HVF expression. However, it has been shown that a more accurate estimation of the load capacity is obtained using the sum of load power losses in the rotor cage from higher harmonics. Measurements and calculations were carried out for a low-voltage squirrel-cage motor with a rated power of 22 kW and a synchronous speed of 1500 rpm. Calculations showed that the derating power curves given in the IEC 60034-17 and NEMA MG1 standards are incorrect for the tested motor.

Real-Time Investigation of Temperature Effect on Induction Motor Equivalent Circuit Parameter Change

Today’s developing technology and increasing demands in production areas continue the importance of studies on induction motors (IMs). To meet the demands, the mathematical modeling of IMs must be performed fully and accurately. Variable conditions cause changes in many electrical, magnetic, and thermal parameters. A change in parameters affects the intensity, efficiency of the operating currents of the machine, thereby changing the motor losses. In this article, the objective is to determine the changes in the equivalent circuit parameters of three-phase squirrel-cage induction motors (SCIMs) with different powers under the variable conditions (stator winding temperature, load, and motor shaft speed). Supervisory control and data acquisition (SCADA) program read real-time information (temperature, current, voltage, power, shaft speed, and torque) from the experiments and necessary calculations were made. When the test results were examined, a maximum of 9 % change was observed in the motor ECPs (RS, R2, RM, XS, X2, and XM) at different shaft speeds as a result of the change in the stator winding temperature between 100 % and 110 %. At different loads, this rate of change increases to 16 %. This has shown that motor shaft speed and load, together with temperature, have a significant effect on the ECPs.

A 2 MW Wind Turbine Simulator for DFIG Wind Energy Generation Systems

This work presents the design and implementation of a wind turbine simulator to carry out laboratory tests on the generation, regulation, and control of a wind power conversion system (WECS) with a capacity of 2 MW. A three-phase squirrel-cage induction motor emulates the static and dynamic wind turbine characteristics based on the torque-speed profile of a wind turbine. The Emulator allows all electromechanical tests to be carried out, from the characterization of the generator to the adjustment of controls and protections for equipment operating in a specific location. Initial Emulator tests were successful. This simulator aims to reproduce the same behavior as a wind turbine, that is, the generator must operate as if it were connected to a real turbine. In this line, a wind profile implemented by using a computer program and its output is used as an input signal. This signal together with the speed measured on the axis serves as the input variable of the emulated turbine.

Detection of Broken Rotor Bars in a Cage Induction Machine Using DC Injection Braking

In this paper, an effective procedure for broken rotor bar (BRB) fault detection in a three-phase squirrel-cage induction machine (SCIM) is proposed. This approach relies on a motor current signature analysis (MCSA) by observing the specific fault-related current component generated by applying the DC injection braking method. Unlike the traditional MCSA, which is commonly focused on the detection of BRB sidebands around the fundamental current component, the proposed methodology introduces a new BRB feature in the current spectrum which makes it much easier for identification. The distinctive time-frequency evolution pattern of this feature provides the reliable identification of BRBs, even under no-load operating conditions, thus overcoming the major drawback of traditional MCSA-based methods. Fault severity classification is easily performed through the magnitude inspection of the BRB fault-related current component. In addition, the proposed approach does not require high-complexity signal processing algorithms to achieve reliable results. The proposed concept is presented theoretically, assisted by a magnetically coupled multiple circuit model of the SCIM, both with healthy and faulty rotor bars. Finally, the experimental tests validate the proposed methodology and demonstrate its effectiveness and usefulness.

MINIMIZATION OF ELECTRICAL CONSUMPTION OF A FREQUENCY-REGULATION INDUCTION MOTOR WITH A FAN LOAD IN START-BRAKING REGIMES

Purpuse. To minimize the total power consumption in start-braking regimes by a three-phase squirrel-cage frequency-regulated induction motor, loaded a centrifugal fan (or smoke exhauster), and also to obtain analytical dependencies for calculating the optimal durations of acceleration and deceleration times, corresponding to minimizing the total energy consumption of this motor in start-braking regimes with the indicated type of load. Metodology. Based on the methods of calculus of variations and numerical solution of non-linear differential equations, the quasi-optimal type of trajectories of speed change (tachograms) of the motor with the considered load in start-braking regimes is determined. Using the methods of mathematical analysis and similarity, the acceleration and deceleration times of an induction motor with a fan load were optimized for different (linear, parabolic and quasi-optimal) types of tachograms. Using the method of computer simulation, the energy consumption in the start-braking regimes of an induction motor with the indicated load for these types of tachograms was quantified. Results. Refined analytical dependencies are obtained for calculating the consumed active power and energy in start-braking regimes by a frequency-regulated induction motor with a fan load for the mentioned various types of tachograms. Analytical optimization of the consumption of active energy of this motor in start-braking regimes has been carried out. The change at the optimal durations for the starting-braking regimes and the corresponding it’s total energy consumption of the motor with varying the maximum value of the motor speed in these regimes has been researched. A quantitative assessment of transient electromechanical and energy processes in the considered motor with a fan load has been carried out. For this motor, as applied to the non-regenerative version of the static frequency converter, a scalar automatic control system is proposed, by means of which the motor accelerates with a constant rotor flux linkage with a given (linear, parabolic or quasi-optimal) speed trajectory and brakes on freewheel. The expected annual saving of active energy by an induction motor, loaded with a smoke exhauster, in starting and braking regimes, achieved by optimizing the form of the tachograms and the duration of the acceleration and deceleration times, is determined. Originality. Analytical dependencies are obtained for calculating the optimal durations of the acceleration and deceleration times of an induction motor with a fan load, corresponding to minimizing the energy consumption of this motor in start-braking regimes. The "U"-shaped form of dependences of the total energy, consumed during acceleration (or the total generated energy during braking) of the induction motor in function the duration of the deceleration (or braking) times is established. An analytical dependence is obtained for changing the speed of a motor loaded by a fan or a smoke exhauster during the freewheel braking regime, and an analytical expression is proposed for determining the duration of the indicated braking time. Practical value. On the example of an induction motor loaded by a smoke exhauster, the possibility of saving the total energy consumption in start-braking regimes was identified: from 77 to 90 % – due to the use of the proposed quasi-optimal tachogram and the use of practically realizable optimal acceleration and deceleration times, and also in the amount of 10 % – through the transition from freewheel braking to regenerative braking. Figures 6, tables 6, references 22.

Characterization of Fault Signature Due to Combined Air-Gap Eccentricity and Rotor Faults in Induction Motors

An accurate means of non-invasive condition monitoring of the popular industrial drive, three-phase squirrel-cage induction motor, can help to avoid unscheduled maintenance downtime and loss. Faults like air-gap eccentricity can exist even in a newly assembled drive and hence may co-exist with other internal defects. Despite it being a possible situation, the occurrence of simultaneous faults has seldom been studied. Therefore, there is a need for identifying fault signatures of combined fault conditions in a non-invasive manner. This paper presents a detailed model-based study on a three-phase squirrel-cage induction motor with the simultaneous existence of broken rotor-bar and air-gap mixed eccentricity faults using spectral analysis of stator current, instantaneous power, and estimated air-gap torque signals. The modelling of the machine is done using the Multiple Coupled Circuit method and modified to model the presence of the combined fault conditions. A comparative evaluation with various fault conditions and their severity is carried out by spectral analysis, and unique slip-dependent frequency components are identified in the spectra of diagnostic signals. This fault characterization is the most significant contribution of this paper.

Mathematical Model and Characteristics of the Induction Motor with a Power Supply from a Current Source

. Methods and mathematical models for studying the modes and characteristics of the three-phase squirrel-cage induction motor with the power supplied to the stator winding from the current source have been developed. The specific features of the algorithms for calculating transients, steady-state modes and static characteristics are discussed. The results of the calculation of the processes and characteristics of induction motors with the power supply from the current source and the voltage source are compared. Steady-state and dynamic modes cannot be studied with a sufficient adequacy based on the known equivalent circuits; this requires using dynamic parameters, which are the elements of the Jacobi matrix of the system of equations of the electromechanical equilibrium. In the mathematical model, the state equations of the stator and rotor circuits are written in the fixed two-phase coordinate system. The transients are described by the system of differential equations of electrical equilibrium of the transformed circuits of the motor and the equation of the rotor motion and the steady-state modes by the system of algebraic equation. The developed algorithms are based on the mathematical model of the motor in which the magnetic path saturation and skin effect in the squirrel-cage bars are taken into consideration. The magnetic path saturation is accounted for by using the real characteristics of magnetizing by the main magnetic flux and leakage fluxes of the stator and rotor windings. Based on them, the differential inductances are calculated, which are the elements of the Jacobi matrix of the system of equations describing the dynamic modes and static characteristic. In order to take into account the skin effect in the squirrel-cage rotor, each bar along with the squirrel-cage rings is divided height-wise into several elements. As a result, the mathematical model considers the equivalent circuits of the rotor with different parameters which are connected by mutual inductance. The non-linear system of algebraic equations of electrical equilibrium describing the steady-state modes is solved by the parameter continuation method. To calculate the static characteristics, the differential method combined with the Newton’s Iterative refinement is used.

A Computer Aided Design of Wedge-Type Rotor-Bars in Squirrel-Cage Induction Motor.(Dept.E)

The deep-bar rotor induction motor is one of the most popular motors in the high starting-torque group of three-phase squirrel-cage induction motors. This motor is commonly fitted with deep-bars, of the wedge-form, on the rotor-side. Optimising the dimensions of these bars is a tedious work, especially when the motor is required to exert a strting-torque which exceeds the normal range. This paper presents a computer aided design of the wedge-type rotor-bar to fulfill this requirement. The design concept, relating the bar-dimensions to the basic group of the motor specifications, is given by taking into consideration the skin -effect just at starting. The iterative method employed to obtain the proper cross-section area of the conductor , as well as the method of checking the preliminary dimensions, are also explained in this paper. The design process is written in form of a digital program which gives for a given output power, the proper bar-dimensions for an extended range of starting-torque ratios. The results show that for a given output power, a starting-torque ratio higher than usual can be obtained on the expense of a little increase in the starting-current ratio.

WIND TURBINE SIMULATION AND CONTROL USING SQUIRREL-CAGE INDUCTION GENERATOR FOR DFIG WIND ENERGY CONVERSION SYSTEMS

This work presents the design and implementation of a wind turbine simulator to carry out laboratory tests on the generation, regulation, and control of a wind power conversion system (WECS) with a capacity of 3 kW. A three-phase squirrel-cage induction motor emulates the static and dynamic wind turbine characteristics based on the torque-speed profile of a wind turbine. The Emulator allows all electromechanical tests to be carried out, from the characterization of the generator to the adjustment of controls and protections for equipment operating in a specific location. Initial Emulator tests were successful.

A new transform discrete wavelet technique based on artificial neural network for induction motor broken rotor bar faults diagnosis

The main objective of this article is to contribute the automatic fault diagnosis of broken rotor bars in three-phase squirrel-cage induction motor using vibration analysis. In fact, two approaches are combined to do so, based on signal processing technique and artificial intelligence technique. The first technique is based on discrete wavelet transform (DWT) to detect the harmonics that characterize this fault, using the Daubechies wavelet vibration analysis according to three axes (X, Y, Z). This application permits having the approximation mode function and the details (recd). To exact choice of reconstruction details which contains the information of the broken rotor bars faults, two statistical studies based on the root mean square values (RMS) and Kurtosis shock factor calculation are carried out for each (recd). The choice of (recd) is conditioned by (RMS) and Kurtosis values as: RMSrecd1 < RMSrecd2 and Kurtosisrecd1 > Kurtosisrecd2. Experimental results showed that (recd1 and recd2) satisfied the condition set for (RMS) and Kurtosis values. At the end of first technique, a spectral envelop of recd1 is adopted to detect the broken rotor bars fault and the second technique based on artificial neural network (ANN) is used to identify the number of broken rotor bars. The characteristics of features used as input variables of ANN are the RMS of recd1 and recd2, and the Kurtosis shock factor of recd1 and recd2. The experimental results demonstrated the high efficiency of the proposed method with rotor broken bars fault classification rate of 98.66%.

On Phase Shifting and Diversified Coil-Pitch for Enhanced Multiobjective Winding Design Optimization

In electric rotating machines, the stator winding design plays a crucial role on their overall performance. Novel approaches for winding design optimization, including multilayer configurations, stator shifting, and phase shifting, have been presented in recent studies. Most of them focus on a single strategy, which is generally applied to one winding topology only. In this paper, a unified and generalized methodology is proposed to solve a two-objective constrained winding design optimization problem, which can be applied to polyphase winding configurations with any number of slots per pole. The novelty concerns the combination of the phase shifting concept with an enhanced end-winding connection strategy, enabled by multiple coil pitches. The framework developed allows for the customization of the objective functions and constraints to the characteristics of the study. Two application examples are provided for validation purposes of the methodology, where time-step finite-element analysis simulations of a three-phase squirrel-cage induction motor and a six-phase permanent-magnet synchronous motor were carried out. The proposed methodology is capable of generating novel winding designs that can potentially improve the machine efficiency and reduce the amount of copper in the stator windings.

An ANOVA-Based Fault Diagnosis Approach for Variable Frequency Drive-Fed Induction Motors

In this article, an analysis of variance (ANOVA)-based fault diagnosis approach using experimental data is proposed for variable frequency drive (VFD)-fed induction motors. Line-to-neutral voltages at the motor terminal and the stator currents, measured from two identical 0.25 HP three-phase squirrel-cage induction motors fed by a voltage source inverter-based low-voltage VFD under healthy and faulty cases, are evaluated. Harmonic spectra of the measured voltage and current are obtained by Discrete Fast Fourier Transform (DFFT). Through the coherence and magnitude consistency analysis, the fundamental and 5th harmonic of the stator current are chosen as “signature frequency components.” ANOVA along with the multiway analysis are then applied to signature frequency components, their mean and standard deviation are identified as “fault signatures”; and the p -value from the inter-group analysis of the mean and standard deviation is used to classify faults. To facilitate fault diagnosis for untested motor operating conditions, formulas to calculate fault signatures are derived by surface fitting using tested data.

Artificial Neural Network and Kalman Filter for Estimation and Control in Standalone Induction Generator Wind Energy DC Microgrid

This paper presents an improved estimation strategy for the rotor flux, the rotor speed and the frequency required in the control scheme of a standalone wind energy conversion system based on self-excited three-phase squirrel-cage induction generator with battery storage. At the generator side control, the rotor flux is estimated using an adaptive Kalman filter, and the rotor speed is estimated based on an artificial neural network. This estimation technique enhances the robustness against parametric variations and uncertainties due to the adaptation mechanisms. A vector control scheme is used at the load side converter for controlling the load voltage with respect to amplitude and frequency. The frequency is estimated by a Kalman filter method. The estimation schemes require only voltage and current measurements. A power management system is developed to operate the battery storage in the DC-microgrid based on the wind generation. The control strategy operates under variable wind speed and variable load. The control, estimation and power management schemes are built in the MATLAB/Simulink and RT-LAB platforms and experimentally validated using the OPAL-RT real-time digital controller and a DC-microgrid experimental setup.

Greedy-Gradient Max Cut-Based Fault Diagnosis for Direct Online Induction Motors

In this paper, a graph-based semi-supervised learning (GSSL) algorithm, greedy-gradient max cut (GGMC), based fault diagnosis method for direct online induction motors is proposed. Two identical 0.25 HP three-phase squirrel-cage induction motors under healthy, single- and multi-fault conditions were tested in the lab. Three-phase stator currents and three-dimensional vibration signals of the two motors were recorded simultaneously in each test, and used as datasets in this study. Features for machine learning are extracted from experimental stator currents and vibration data by the discrete wavelet transform (DWT). To validate the effectiveness of the proposed GGMC-based fault diagnosis method, its classification accuracy using binary classification and multiclass classification for faults of the two motors are compared with other two GSSL algorithms, local and global consistency (LGC) and Gaussian field and harmonic function (GFHF). In this study, the performance of stator currents and vibration as a monitoring signal is evaluated, it is found that stator currents perform much better than vibration signals for multiclass classification, while they both perform well for binary classification.

Threshold-Based Induction Motors Single- and Multifaults Diagnosis Using Discrete Wavelet Transform and Measured Stator Current Signal

In this article, a threshold-based induction motor fault diagnosis method is proposed using the measured stator current signal. A 0.25-HP three-phase squirrel-cage induction motor fed directly online is tested in the laboratory with various single- and multielectrical faults under six different loading conditions. The discrete wavelet transform (DWT) is chosen as the signal processing technique for the measured stator currents. The threshold and energy values at each decomposition level of the DWT processing results are evaluated. Threshold values appear to be more consistent than energy values at different measured data windows, and thus, the threshold at the decomposition level d8 is chosen as a fault indicator. Curve fitting equations are developed to calculate threshold values for the motor loadings that were not tested in experiments. The suitability using threshold values for induction motor fault diagnosis is further validated using two probabilistic methods, the correlation analysis and the confidence interval estimation.