Determination of starting current in three-phase induction motors

The author reviews the existing conversion methods which determine the starting current in three-phase induction motors and points out their weaknesses. A theoretical base is found for the determination of starting current, and an accurate method called the regression estimate method is proposed     

Performance optimization of induction motors during Voltage-controlled soft starting

This paper deals with the performance optimization of medium/high-power induction motors during soft starting by eliminating the supply frequency torque pulsations, and by keeping the line current constant at the preset value. Starting torque pulsations are eliminated by triggering back-to-back-connected thyristors at proper points on the first supply voltage cycle. Line current during starting can be kept constant at any preset value by a simple strategy composed of successive cosinusoidal and constant function segments of the triggering angle. These strategies are implemented by the use of an 8-b microcontroller. Transient performance analyses of the system are carried out by means of a hybrid ABC/dq machine model which takes into account the three-phase, two-phase, and disconnected modes of operation in terms of actual stator variables. Experimental results obtained on a custom-design test bed are found to be in good agreement with the theoretical ones.     

A nonconventional method for fast starting of three phasewound-rotor induction motors

This paper presents a nonconventional method for the fast starting of three-phase wound rotor induction motors. This is achieved through shunting the stator and rotor windings across the supply for a predetermined short period. By this connection, the motor produces an extremely high starting torque. The feasibility of this basic idea has been confirmed through investigating the starting transients corresponding to this mode of operation. For this purpose, a rigorous state-space mathematical model has been developed and simulated. The validity of the proposed method and the findings from the mathematical model have been confirmed experimentally     

A comparative study on the starting methods of three phasewound-rotor induction motors. I

This paper presents a comparative study on the starting performance of three phase wound-rotor induction motors under different methods of starting. These methods are online direct starting, variable rotor resistance starting and double feed starting. In the double feed starting, the rotor winding is connected in parallel with the stator winding across the supply for a predetermined short period. By this connection, the motor produces an extremely high starting torque. For carrying out the investigations sought, a rigorous state space mathematical model has been developed and simulated. The effect of torsional dynamics has been taken into considerations     

Transient thermal analysis of induction motors

Induction machines transient thermal analysis has been a subject of interest for electric machine designers in their effort to improve machine reliability and in rotor design optimisation. The study of transient thermal behavior is useful to identify causes of failure in induction machines. This paper presents a 2-D transient analysis of induction machines using the available heat transfer coefficients in literature. A generalised finite element code developed with Galerkin's weighted residual technique is used for analysis. The model is applied to one squirrel-cage totally-enclosed fan cooled machine of 3.7 kW and another surface cooled machine of 5.7 kW. The predicted temperatures compare well with test results. The advantages and limitations of this model are discussed     

PSPICE simulation of single-phase induction motors

Dynamic analysis of a single-phase induction motor is studied using PSPICE software. The machine dynamics are presented by a set of nonlinear time-varying differential equations. The equations which define the motor operation are represented in an orthogonal system. The electric circuit presenting this set of equations is determined and solved by PSPICE software for simulation of the motor. The simulation results are compared with those obtained by EMTP and the experiment. Good agreements are observed for both cases     

Tracking control technique for induction motors

A novel application is presented of the tracking control technique to induction motor drive systems. By this technique, the position or the speed of the rotor can follow a preselected track (a time history of rotor position or velocity). An algorithm for the design of the tracking controller is developed. The induction motor model and the controller are modified to allow the inclusion of the nonlinear modes in the system without excessive computations. A simple and realistic criterion for selecting the proper reference tracks during starting, speed control and braking is proposed. The controller developed, is tested on a full-size nonlinear analog simulator. All test results show the effectiveness of the scheme in position-tracking applications such as robotics and manipulators     

Parasitic torques in saturated induction motors

A method for analyzing the performance of induction machines for parasitic torques is described. Such torques arise from the interactions of fundamental and harmonic components of air flux density due to geometrical considerations such as slotting, and saturation effects. Parasitic torques arise under balanced sinusoidal drive conditions. However, they are greatly exacerbated under nonsinusoidal drive conditions. The technique described for analysis is applicable to both cases     

Analysis of torsional torques in starting of large squirrel cageinduction motors

The paper presents a comprehensive study of the starting process of a large squirrel cage induction motor driving an inertia load through an elastic shaft. The analysis of the electromagnetic torque of the motor has revealed that there are variable frequency components which interact with the torsional mode of the mechanical system and produce hazardous shaft torque. This torque may exceed the maximum yield of the shaft or it may accumulate and result in a cyclic fatigue fracture. The nature of the problem is explained and the factors which aggravate its impact are discussed. Furthermore, it is shown that the torsional torque can be substantially reduced by the proper coordination of the switching operations     

Harmonic losses of single-phase induction motors undernonsinusoidal voltages

Parameters of a capacitor-start, capacitor-run single-phase induction motor with closed or semi-closed rotor slots are measured and a model for the investigation of the performance of the machine in the frequency domain under the influence of harmonic voltages is presented. An algorithm, taking into account the nonlinear rotor leakage inductance, is established. This algorithm is applied to estimate the current in the time domain, and the harmonic losses at rated-load operation without and with run capacitors are calculated. Computational results are compared with those from experimentation and the differences between both are discussed     

Operation of three-phase induction motors connected to one-phasesupply

The behavior of a three-phase induction motor is analyzed operating according to the Steinmetz connection, conceived to allow operation of small rating motors connected to a one-phase supply and with a small degree of voltage unbalance. The conditions for canceling the negative sequence component of the stator winding terminal voltages and currents are also established. The increase in electromagnetic torque deriving from balancing with capacitors and the overvoltages closely related to the changes in amplitude and phase of positive sequence motor impedance verified during rotor acceleration are emphasized. Results presented by considering a capacitor in parallel to one of those phases connected to the motor terminal switched off from the three-phase supply define the requirements for correct capacitor selection and switching off in order to obtain proper motor behavior in the whole slip range from starting to the final operating point. A careful evaluation of the amplitude and phase of the positive sequence impedance should be taken into account for capacitor application to be considered in reducing the degree of unbalance during motor starting and even in normal operating slip range. This will be very useful for reliable capacitor specification and for properly defining rotor speeds at the instant of capacitor switching off     

Losses influenced by third-harmonic flux in induction motors

The trend toward increasing flux density in modern induction motors results in the increase of third-harmonic flux in the magnetic paths. The effects of third-harmonic flux on energy losses in induction motors are discussed. The shapes of flux distributions in various sections of an induction motor are interrelated. The most saturated section normally has a flattened shape of flux density distribution. The effects of the shapes of flux density distribution on losses are compared from the third-harmonic flux standpoint. The losses influenced by the third-harmonic flux may be controlled through lamination punching designs and winding connections     

Reclosing torques of large induction motors with stator trappedflux

Large induction motors are subjected to high transient torques following the rapid reconnection of the supply. The paper shows that these torques have oscillatory components with speed dependent frequencies. These components may result in high torsional torques if the supply is reconnected at an unfavorable instant; when the frequency of one of the torque components coincides with the natural torsional frequency. However, this high torque can be avoided by the proper choice of the reclosing instant     

A new method for quality monitoring of induction motors

Catalog data of three-phase induction motors specify values of some operational parameters in addition to the nameplate information. These parameters include the efficiency, power factor, starting current, maximum torque, rated torque, and starting torque. At the end of the manufacturing process, extensive testing is required to ensure that a specific motor meets the specifications. In this paper, a method is presented to ensure that the motor meets the operational parameter specifications, including the tolerances that might be imposed using the results only of the no-load test and the blocked-rotor test     

Failure identification of induction motors by sensing unbalancedstator currents

A technique suitable for real-time failure monitoring of cage induction motors is presented. The proposed method utilizes online sensing of the unbalance in the stator current signal to assess the integrity of the motor. This approach is extremely effective where the system neutral is high resistance grounded. The sensor is inexpensive, noninvasive, reliable, and easy to install. Instead of analyzing the spectral components of the signal, the absolute magnitudes are used for identifying the incipient failure; therefore, the need for computing and data processing is partly eliminated. This method is tested for wye connected motors. The results from laboratory investigations are presented. The usefulness of this approach is demonstrated with the aid of simulated fault conditions in the experimental motor. The efficacy of the proposed method in industrial power systems is discussed     

Modeling and simulation of saturated induction motors in phasequantities

This paper proposes a new model for saturated induction motors. The saturation effects are incorporated in the magnetizing inductance and the stator mutual inductances, taking into account the nonuniform distribution of magnetic saturation within the motor core. The proposed model can be used to analyze the manner in which the induction motors interact with the supply network or power source, since it can predict the motor current/voltage harmonics produced by magnetic saturation. Experimental tests show that the proposed model represents with reasonable accuracy (8%) the motor saturation effects at nominal stator voltage as well as for overvoltage operation     

Application of fuzzy logic to induction motors condition monitoring

This letter applies fuzzy logic to induction motors condition monitoring. The preliminary results show that fuzzy logic can be used for accurate induction motors fault diagnosis if the input data are processed in an optimized way     

A step-down chopper-controlled slip energy recovery induction motordrive

The design of a chopper-controlled slip energy recovery drive, also known as a static Kramer drive, demands an exact knowledge of the steady state and dynamic performance of the system over the complete operating range. To accomplish this, a coupled circuit approach is necessary whereby the self and mutual coupling effects, voltage and current harmonics in the machine and voltage and current ripple at different points in the drive system are duly taken into account. Such a model should enable the accurate prediction of all instantaneous current values which leads to accurate prediction of electric torque and harmonics injected into the supply. This paper presents a model to accomplish the above. Mathematical predictions are verified with experimental results     

Harmonic analysis of slip energy recovery induction motor drives

The impact of electric drives on the power system in terms of harmonic generation is becoming increasingly important. Slip energy recovery induction motor drives (SERIMDs) have the rectifier and inverter connected to the rotor instead of the stator (the case in most conventional drives). The harmonic content of the SERIMD is thus quite different and arguably, less onerous than conventional drives. This paper examines the harmonic content of key waveforms of SERIMDs. Predicted results are supported by extensive experimental results     

A review of stator fault monitoring techniques of induction motors

Condition monitoring of induction motors is a fast emerging technology for online detection of incipient faults. It avoids unexpected failure of a critical system. Approximately 30-40% of faults of induction motors are stator faults. This work presents a comprehensive review of various stator faults, their causes, detection parameters/techniques, and latest trends in the condition monitoring technology. It is aimed at providing a broad perspective on the status of stator fault monitoring to researchers and application engineers using induction motors. A list of 183 research publications on the subject is appended for quick reference.