The improvement of the electrical insulation of high voltage electrical machines

Comparative parameters are presented for the electrical insulation systems of high voltage electric machines. Composite insulation materials produced by different manufacturers are studied. The influence of the structure and composition of electrical insulation materials on the main operation parameters (electric strength, dielectric losses, the mechanical characteristics, and resistance to thermal cycling) of the insulation systems of electric machines is shown.     

Analysis of electrical machines using Symphony

The application of Symphony spreadsheet programs to electrical machine analysis is described. Seven typical examples are presented, namely steady-state performance of a DC shunt generator, speed control of a DC shunt motor, magnetizing current waveform of a transformer, steady-state performance of a three-phase induction machine, frequency control of a three-phase induction motor, induction motor run-up, and swing curves of a synchronous generator. Advantage is taken of the spreadsheet environment for such operations as tabular calculation, table lookup, numerical integration, and what-if analysis. Extensive use is made of the integrated graphics facilities of Symphony for producing good quality screen displays on a personal computer, which proves very convenient and useful for computer-aided instruction. Certain features of Symphony are described in the context of the applications described     

Model reference adaptive control applied to electrical machines

This contribution reports about a discrete-time robust adaptive control strategy for single-input/single-output systems with arbitrary zeros. The adaptive algorithm is mainly based on a direct model reference method. The basic idea presented here is to divide the feedback law into a direct adaptive and a fixed part. By a certain choice of the non-adaptive controller parameters the robustness of the adaptive control loop with respect to unmodelled dynamics of the plant may be increased. The non-adaptive part of the controller can be reformulated as a bypass to the plant and will be denoted as the ‘correction network’ owing to its action on the open-loop zeros of the augmented plant. The new adaptive control strategy removes the major drawbacks of model reference control and is investigated for speed control of a DC motor and voltage control of a synchronous generator.     

ELMEC software system for the design and investigation of electrical machines

An implementation in the ELMEC software system is presented for the method for computing the electromagnetic field in an electrical machine, which relies on the precision numerical simulation of electrodynamical processes. The basic simulation principles are stated, along with the structural features of the ELMEC software system, the use of which allows essentially improving the quality of design and optimization in the development of electrical machines.     

New electric insulating materials for the insulation systems of rotating electrical machines

A wide range of nomenclature and properties for new materials for the insulation of high voltage electrical machines and traction motors of F and H insulation classes developed at Elinar Holding Company are presented in the report.     

On the theory of main flux saturation in smooth airgap electrical machines

Contents The physical foundation of the theory of the smooth airgap machine with main flux saturation taken into account is carefully examined with special reference to the justification of the simplifying assumptions commonly used when the transient equations are established. An experiment showing the nature of the magnetic interaction between coils in quadrature is demonstrated. Measured and computed results are compared.

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Über die Theorie der Sättigung des magnetischen Hauptflusses in Zylinderläufermaschinen

Übersicht Die physikalischen Voraussetzungen und die notwendigen Vereinfachungen in der Theorie der Zylinderläufermaschine bei veränderlicher Sättigung des magnetischen Hauptflusses sind genau formuliert und präzisiert. Es wird ein Experiment beschrieben, das die Messung der induktiven Kopplung zwischen zwei Spulen erlaubt, deren Achsen senkrecht zueinander stehen. Die durch Messung genauen Resultate werden mit den numerisch berechneten Ergebnissen verglichen.

     

A new introductory electrical engineering curriculum for thefirst-year student

This paper reports on the author's experience with respect to a major revision of the introductory Electrical Engineering curriculum at Worcester Polytechnic Institute. The new curriculum incorporates classroom and laboratory experience in electrical engineering for first-year students. The new courses are based on the “spiral” approach to education in which concepts are introduced at an applications-oriented level, and then repeatedly revisited with successively greater levels of detail and theoretical sophistication. The plan that has been adopted was the result of extensive study within the department in which current students and alumni participated through surveys. An assessment plan and preliminary assessment results are discussed     

Space-phase 2D simulation of electromechanical transformation in electrical machines

A space-phase method for the mathematical simulation of electromechanical energy transformation in electrical machines of rotational motion is proposed. Results of numerical experiments with two-dimensional space-phase models of a reverse-design valve machine with constant magnets are presented.     

High-frequency electromagnetic processes in electrical machines under pulse-width voltage modulation

The paper considers models and features of electromagnetic processes in systems, including electrical machines and semiconductor PWM converters. It is shown that tagging into account parameters and characteristics of high frequency electric processes is necessary in designing new electrical systems.     

Vibratory behavior reduction of electrical machines through materials properties evaluation

Most of the electromagnetic devices, especially electrical machines, have the disadvantage to be exposed to high vibrations caused by magnetic forces. The aim of this study is to propose a methodology to optimize the cylindrical stators generally used in electrical machines regarding the vibration phenomena. Techniques for vibration reduction require knowledge of the proper frequencies, which depend on mechanical shapes and dimensions as well as material properties such as mass density, Young's modulus and Poisson's ratio. This paper proposes a new approach which is based on the identification of mass density (lamination stacking factor) and Young's modulus in the goal to minimize the vibratory behavior of electrical machines. In this goal, we have used artificial intelligent and finite element method (FEM) analysis to solve the magneto‐mechanical inverse problem (IP). In the proposed approach, a Multilayer Perceptron Neural Network (MLPNN) is used as a forward model in order to decrease the FEM time consuming. Thus, a Genetic Algorithm (GA) is used to solve the IP in a reasonable time of running. An example study of an induction machine proves that the developed approach may be applied in both design and identification applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of magnetomotive forces of fractional-slot windings of electrical machines

The winding coefficient is obtained based on the analysis of magnetomotive forces of fractionalslot windings with q < 1. The analysis enables one to consider all types of electrical machines (inductor, multipolar with constant magnets, with rolling rotor with pulsating flow, etc.) with fractional-slot windings from uniform positions.     

Representation of skew in time-stepped two-dimensionalfinite-element models of electrical machines

The authors outline a technique which enables two-dimensional finite-element analysis to be applied to skewed machines. It involves representing the continuous skewing in a series of discrete steps. Each step may be modeled in two dimensions. The model has been applied to a salient-pole synchronous generator and to a cage induction motor. It is shown that the model is successful in removing phantom slot-ripples from the current and voltage waveforms     

Measures and technologies to enhance the insulation condition monitoring of large electrical machines

The utility of condition monitoring of the stator insulation structure of large machines has been enhanced substantially by the use of computer-based analysis of partial discharge signatures. A number of indices are examined through tests in a multistress aging facility to assess their promise in describing insulation degradation in machine insulation. In transitioning such tests to the field environment, an operational test is also described which offers some promise in identifying degradation without prior baseline data for a machine. On the basis that most electrical failures have mechanical precursors, acoustic methods are described for assessing stator bar mechanical integrity. This includes both using the conductors as waveguides and also employing acoustic emission for the location of large discharges.     

A new approach to designing electrical machines on the basis of numerical simulation

An approach that enables one to calculate the electromagnetic field in an electric machine in conjunction with the calculation of currents in windings and the rotation of a rotor under the effect of electromagnetic forces and loads is considered. The capacities of the considered methods for designing electrical machines are demonstrated for a number of examples. The calculated results are compared with the experimental data obtained for an induction electric motor with two short-circuited windings on the rotor.     

Medium frequency shaft voltages in large frequency converter driven electrical machines

The operation of large electrical machines like turbo-generators with ratings of several hundred MVAs by static frequency converters can cause shaft voltages of several hundred volts. The shaft voltages consist of peaks with a time constant of some μs. They occur mainly during the rectifier switching at the grid-linked section of the converter. The voltages are the result of a coupled capacitive and inductive phenomenon. The root cause of these voltages is shown and a machine model of turbo generators for several 10 kHz is developed taking parasitic capacities and eddy currents into account. It is not sufficient to limit the model just to the generator. It is the combination of transformator, cables, frequency converter and generator, which allow for such high voltages. Comparisons with measurements on a 300 MVA generator are made to verify the model. A high level of agreement between measurement and calculation is reached for this recently discovered capacitive inductive shaft voltage phenomenon. Especially the high power class of the equipment involved reveals the underlying physics fairly clearly, but enforces a deep investigation and high predictability of the right counter measures in order to avoid substantial risk exposures.     

Finite-element modeling of thermal contact resistances andinsulation layers in electrical machines

Small transition layers with a significant temperature drop, such as thermal contact resistances and thin insulation layers, are difficult to consider in coupled finite-element thermal/magnetic models of electrical machines. A novel approach using mesh cuts and duplicated nodes at the thin-layer position is derived and discussed here. Results are compared to classical methods involving the use of nonscaled and scaled finite elements. Practical examples demonstrate the features and implementation aspects of the methods used     

The application of space-vector theory to the analysis of electrical machines with space harmonics

Contents In the present paper the space vector method is described for the analysis of uniform air-gap three-phase and two-phase machines, taking into account the effects of m.m.f. space harmonics.The space vector equations are established in a natural and also in an arbitrary reference frame. It is shown that the various harmonic models can obtained without performing matrix transformations. The relationship between matrix and space vector forms is discussed. The models derived are suitable for both steady-state and transient analysis. Methods of derivation of harmonic transformations are also presented.

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Die Anwendung der Raumzeigertheorie zur Analyse elektrischer Maschinen mit räumlichen Obserwellen

Übersicht In der vorliegenden Arbeit wird die Methode der Raumzeiger zur Darstellung räumlicher Oberwellen in elektrischen Maschinen betractet. Die allgemeinen räumlichen Vektorgleichungen werden in einem natürlichen bzw. in einem beliebigen Koordinatensystem beschrieben. Es wird gezeigt, daß die verschiedenen harmonischen Modelle ohne Matrizenoperationen erhalten werden können. Die Beziehungen zwischen den Matrizen- und Raumzeiger-schreibweisen werden untersucht. Die Darstellungen der Maschine sind für die Analyse stationärer und nichtstationärer Vorgänge anwendbar. Schließlich wird die Ableitung harmonische Transformationen berücksichtigt.

     

On the variation with flux and frequency of the core loss coefficients in electrical machines

A model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients are variable only with the induction, is proposed. A procedure for identifying the model coefficients from multifrequency Epstein tests is described, and examples are provided for three typical grades of non-grain-oriented laminated steel suitable for electric motor manufacturing. Over a wide range of frequencies between 20-400 Hz and inductions from 0.05 to 2 T, the new model yielded much lower errors for the specific core losses than conventional models. The applicability of the model for electric machine analysis is also discussed, and examples from an interior permanent-magnet and an induction motor are included.