A comparison of two and three dimensional analysis of linear induction machines

It is attempted to classify the advantages and drawbacks of the two dimensional and three dimensional analysis of linear induction motors. Thrust and normal forces have been evaluated by various methods, and compared with results obtained with two motors. The range of Reynold's number was between 3 and 15, therefore including a motor with low and high extremity effect. Computing problems have been considered.     

Lumped-parameter thermal model for induction machines

A novel lumped-parameter thermal model for induction machines that can be included in real-time applications is presented. The model considers just stator, rotor, and environment representative temperatures so that parameter estimation can be carried out. Thermal parameters are experimentally obtained and a sensorless vector control application with a 1-kW induction motor is included showing the effectiveness of the proposed solution.     

Electromagnetic emissions from electrical rotating machinery

The problem of evaluation of the electromagnetic emissions from large power electrical rotating machinery is considered. The results of three measurement campaigns are reported: emissions are correlated with the operating conditions and the characteristics of the machine under test. The measured electric and magnetic field spectra are treated so that they may be used as a reference for preliminary evaluation on similar machines     

Advances in online monitoring and localization of partial discharges in large rotating machines

Some of the problems facing partial discharge (PD) measurements in rotating machines, especially during online measurements are: i) calibration of the measurements; ii) high noise levels interfering with both the measurement system and the winding under the test; as well as iii) attenuation and distortion of PD signals during transmission from the source point to the winding terminals. This paper presents a new technique and a measuring system for online PD monitoring of large rotating machines, developed by the authors. With this technique, the above mentioned problems are improved considerably. PD detection is implemented for every stator coil and the coil that PD comes from can also be identified. Inductive coils are used for decoupling of PD pulses and processing of the detected signals is in accordance with the developed technique, denoted "Intech". Remote monitoring and navigation via a telephone link is one of the system features. The system was tested on both hydro and turbo generators with good results. The detection sensitivity of the system for the conventional machines is about 1 nC under operating condition.     

Asymmetrical constants and effect of joints in the secondaryconductors of a linear induction motor

In this paper, one method of identification of the linear induction motor (LIM) constants is presented. Beside the asymmetrical nature of the LIM's constants (because of finite winding lengths) it was noticed that when a joint in the secondary conductor moves inside the active area of the LIM it creates variation and fluctuation of the secondary resistance of the LIM. The variation and fluctuation of the secondary resistance affects the thrust of the LIM which also fluctuates. These fluctuations of the thrust are not acceptable in some applications such as linear motor elevators in which the riding comfort is very demanding. A hardware solution to diminish the fluctuations of the thrust is proposed. It consists of adding a secondary joint at half pole pitch distance from the primary joint. This second joint creates another fluctuation that opposes the fluctuation caused by the primary joint. Thus, the secondary joint cancels the fluctuation effect caused by the primary joint. Several experiments were performed to confirm this solution     

Analysis of generically configured PSC induction machines

A multiple reference frame based model of a generically configured permanent split capacitor (PSC) induction machine is set forth. The model provides for the possibilities of asymmetrical winding arbitrary tapping of the main winding, and shifting of the auxiliary winding from the quadrature position. The model is valid for both steady-state and transient analysis, and features state variables which are constant in the steady-state. This feature makes the model readily linearizable for derivation of transfer functions. In addition, a procedure for estimation of the machine parameters based on standstill measurements is set forth. Finally, both the model and the parameter measurement scheme are verified experimentally     

Losses in three-phase induction machines fed by PWM converter

The paper deals with the analysis and evaluation of test results of PWM converter-fed induction motors. The test results presented point out the dependency of the harmonic losses on the pulse frequency. The measured values were obtained by means of a novel high precision power-analyzer capable of measuring the harmonics of voltage, current and power. Following a detailed investigation regarding the sources of the harmonic losses the paper describes new methods for determining the harmonic losses by both calculation and measurement. The calculation is based on a new equivalent circuit comprising specific impedances for imaging the eddy-current circuits within the iron core derived from the fundamental equations of the three-phase asynchronous machine. These impedances permit the calculation of the harmonic iron losses under the influence of the eddy-currents in all sections of the magnetic circuit caused by the harmonics. Measured and calculated losses were found to correspond satisfactorily for the various voltage harmonics     

Noise and vibration from induction machines fed from harmonicsources

Electrical machines are increasingly being fed from supplies containing significant harmonic content. This is true both in conventional systems where harmonic levels are steadily increasing and in variable speed drive voltage-source inverters which are being used in ever greater numbers. This paper examines how the noise and vibration level of machines is affected by increased levels of distortion and also how the vibration is affected by machine loading. The methods described apply to a wide range of machine applications     

Simulation of the impulse response of electrical machines

This paper presents three different methods for modeling the transient response of electrical machines. The state-space approach, the Laplace transformation technique and the realization of a new, wide-frequency range equivalent circuit of the machine terminal impedance are applied to obtain the transient response to any waveform. The introduced methods are based on the frequency response of the machine which is often seen as a black box. Both laboratory- and large-scale machines are used to investigate the effect of a variety of impulse waveforms on the transient response of the other phases and to obtain the voltage distribution along the winding of each phase. A frequency response test for the machine is applied to obtain the resonance frequencies and the rational forms for both the voltage gains and terminal impedance. Excellent agreement (error is within 3%) is found between the three methods and the experimental results for different types and ratings of electrical machines under different impulse waveforms     

Experience with directional couplers for partial dischargemeasurements on rotating machines in operation

Manitoba Hydro applied directional couplers for on-line partial discharge measurements on selected rotating machines beginning in 1981. With the instrumentation available at that time the measurement was vulnerable to the effects of noise external to the machine. There have been improvements in the available coupling capacitors which have allowed selection of more optimum measuring locations. In addition, new instrumentation has become available which allows some of the more serious noise problems to be overcome. The paper describes these developments as well as some of the stator winding problems which have been detected     

AN improved method of optimization for electrical machines

Methods of optimizing the design of electrical machines are discussed. The augmented Lagrangian multiplier method is described, and an algorithm for this method is introduced. The method is compared with the more familiar exterior penalty function method using, as an example, the cost optimization of permanent magnetic variable-speed drive motors. The improved method is shown to be superior, both in its ability to reach an optimum consistently and in the number of required iterations     

Estimating the parameters of induction machines at standstill

This paper presents a method to determine the continuous-time parameters of induction machines which are necessary to implement a field- oriented control strategy. This method does not require the use of any mechanical devices or speed measurement sensor and it is conceived to be used during the auto-commissioning of the drive-system. The estimation of the stator resistance is based on the dynamic model of the machine considering that the variables are DC quantities. The estimation of the stator transient inductance, the stator inductance, and the rotor time constant, are based on the dynamic model of the machine. The experimental results which are presented demonstrate the feasibility of the proposed method     

Three phase induction machines asymmetrical faults identificationusing bispectrum

Bispectrum analysis is introduced for three-phase induction machine faults identification and condition monitoring. Bispectrum analysis is capable of providing more information than power spectrum analysis. In the present investigation, machine vibration signals operating at different rotating speed and degree of unbalance are thoroughly analyzed. Very promising results were obtained and presented. The results and analysis indicate that bispectrum analysis can be successfully applied to machine asymmetric faults, machine rotation speed and stator winding fault analysis and identification     

Motional time-harmonic simulation of slotted single-phase induction machines

Considering motional effects in the steady-state finite-element simulation of single-phase induction machines inevitably requires a transient approach. The resulting computation time seriously hampers the application of finite elements within technical designs. In this paper, time-harmonic finite-element simulation, as commonly applied to the three-phase induction machine model, is also enabled for single-phase motors by decomposing the air-gap field in two revolving fields in the opposite direction. The advantages and drawbacks of the novel approach are illustrated by a benchmark model. Issues such as ferromagnetic saturation, external circuit coupling, adaptive mesh refinement, and torque computation are addressed. The method is used to simulate a capacitor start/run motor.     

IGSPICE simulation of induction machines with saturable inductances

A novel approach to the dynamic analysis of induction machines with saturable inductances is presented. The machine dynamics are represented by a set of nonlinear time-varying differential equations. The machine parameters (i.e. saturable inductances) are modeled by closed-form nonlinear functions. The equations which define the machine operation are modeled by d and q equivalent circuits. The equivalent circuits are simulated using the IGSPICE software package     

Practical considerations concerning impulse voltage testing ofform-wound coils for rotating machines

The authors review the response of the windings of high-voltage AC rotating machines to system-generated transient voltages and also impulse test techniques and withstand levels of form-wound stator coils. Design tests on coils with a vacuum pressure impregnation (VPI) insulation system have confirmed very high turn-to-turn insulation strength well above actual system transient voltages. Because of this and since the amplitude of line-to-ground overvoltages to which windings are exposed in service can be controlled to some extent, there appears to be no need for impulse testing of complete machines. Also, the line-to-ground withstand capability of a winding would be adequately verified by the standard AC applied potential test. If, under special conditions, the actual turn-to-turn insulation strength must be demonstrated experimentally, such tests should be performed on additionally fabricated sacrificial coils which are manufactured with and identical to those in the winding     

Application of AI tools in fault diagnosis of electrical machines and drives-an overview

Condition monitoring leading to fault diagnosis and prediction of electrical machines and drives has recently become of importance. The topic has attracted researchers to work in during the past few years because of its great influence on the operational continuation of many industrial processes. Correct diagnosis and early detection of incipient faults result in fast unscheduled maintenance and short down time for the machine under consideration. It also avoids harmful, sometimes devastative, consequences and helps reduce financial loss. Reduction of the human experts involvement in the diagnosis process has gradually taken place upon the recent developments in the modern artificial intelligence (AI) tools. Artificial neural networks (ANNs), fuzzy and adaptive fuzzy systems, and expert systems are good candidates for the automation of the diagnostic procedures. This present work surveys the principles and criteria of the diagnosis process. It introduces the current research achievements to apply AI techniques in the diagnostic systems of electrical machines and drives.     

Pattern recognition-a technique for induction machines rotor brokenbar detection

A pattern recognition technique based on Bayes minimum error classifier is developed to detect broken rotor bar faults in induction motors at the steady state. The proposed algorithm uses only stator currents as input without the need for any other variables. Initially, rotor speed is estimated from the stator currents, then appropriate features are extracted. The produced feature vector is normalized and fed to the trained classifier to see if the motor is healthy or has broken bar faults. Only the number of poles and rotor slots are needed as pre-knowledge information. A theoretical approach together with experimental results derived from a 3 hp AC induction motor show the strength of the proposed method. In order to cover many different motor load conditions, data are obtained from 10% to 130% of the rated load for both a healthy induction motor and an induction motor with a rotor having 4 broken bars     

Broken rotor bar detection in induction machines with transient operating speeds

Previous work on condition monitoring of induction machines has focused on steady-state speed operation. Here, a new concept is introduced based on an analysis of transient machine currents. The technique centers around the extraction and removal of the fundamental component of the current and analyzing the residual current using wavelets. Test results of induction machines operating both as a motor and a generator shows the ability of the algorithm to detect broken rotor bars.