bluuebunny/crossref_metadata_2025 huggingface dataset:
Additional core losses in induction machines with pwm inverter
Authors: Wahsh S. , El‐Bakry M.
Published: July 2010

Induction machine drives with squirrel‐cage rotor will more and more replace the DC motor for its various advantages. The additional motor losses are essentially copper and iron losses in stator and rotor. Iron losses are significantly influenced by machine construction, magnetic materials used and supply type. Different formulae and estimations are given in the literature for these losses. In this contribution a method is presented for the calculation of additional iron losses in induction machines with PWM inverter. Two limits are deduced for the calculation of eddy‐current losses, within which the losses lie, and which agree with the theoretical basis and most empirical formulae given in the previous works. Similarly a new method is proposed for the additional hysteresis losses. The proposed methods give good results compared with the other known methods.
Contribution to the clarification of partial discharge behaviour in insulating liquids using the schlieren technique
Authors: Borsi H. , Gockenbach E. , Schröder U. , Schiller G.
Published: July 2010

This article describes some investigations concerning the process of partial discharges (PD) in insulating liquids by comparing optical and electrical characteristic quantities of PD. The PD behaviour is recorded by synchronized Schlieren photos and oscillograms. The results of these investigations allow to establish a connection between optical and electrical characteristic appearances. The results are interpreted and discussed with the well known streamer theory.
Calculating the effects of solid‐rotor material on high‐speed induction motor characteristics
Authors: Pyrhonen J.
Published: July 2010

A method for the analysis of high‐speed solid‐rotor induction motors is presented. The analysis is based on a new combination of the three‐dimensional linear method and the transfer‐matrix method. Both saturation and finite length effects are taken into account. The active region of the solid rotor is divided into saturated and unsaturated parts. The time dependence is assumed to be sinusoidal and phasor quantities are used in the solution. The method is applied to the calculation of smooth solid rotors manufactured of different materials. Five rotor materials are tested: three construction steels, pure iron and a cobalt‐iron alloy. The results obtained by the method agree fairly well with the measured quantities.
Database/power‐flow interlinkage of a stand‐alone power system training simulator
Authors: Rumpel D. , Nagdy N. M. , Ader T.
Published: July 2010

A training simulator imitates the performance of a power system by application of dynamic models for power units, networks and loads. The results must be displayed in a form related to real operation. This implies a presentation of the power system both on operational and on model level, and transitions between both levels. The GDL‐system allows to describe the whole operational stock of objects, e. g. for substations, bays, lines, protection and auxiliary equipment alarms, including their potential topology, in format‐free alphatext. This source is translated into a data model according to general rules. From the data model an operational man/ machine interface is automatically derived. The dynamic model of the simulator was already presented by K. Dickers and D. Rumpel in „Modelling for Grid Restoration Studies „(Electr. Power&Energy Systems Vol. 9 (1987) No. 1, pp. 45‐55). The present paper shows, how the power flow of the dynamic model is automatically linked to the GDL data model, without further program adaptions or parametrizing efforts on model level.
MODELS: A new simulation tool in the emtp
Authors: Dubé L. , Bonfanti I.
Published: July 2010

MODELS is an autonomous general‐purpose simulation program recently interfaced to two versions of the Electromagnetic Transients Program (EMTP). This interfacing enables the description of components that could not be represented easily until now using the electrical elements of the EMTP and the set of control blocks available in its TACS (Transient Analysis of Control Systems) section. This paper evaluates the usage of MODELS in the EMTP by stressing the differences in approach and use as compared to TACS. An application example is provided and discussed.
Computer aided partial discharge testing of thin solid insulation systems
Authors: Koch H. , Pfeiffer W.
Published: July 2010

For the assessment of thin insulation films in electrical equipment and components a computer aided partial discharge (PD) measuring system is presented. Those insulations are e. g. used in optocouplers, transformers, capacitors and all kind of coating, for instance on printed circuit boards (PCB). The test specimen are taken out of industrial production and are typical for the present manufacturing standard. Two types of test results are presented: Type I shows the PD‐behaviour for long time stress with the test voltage kept constant at a value not higher than ].5 times the PD‐inception voltage (Uj). Type 2 shows the PD‐behaviour for short time stress when the test voltage is increased continuously up to the breakdown voltage of the test specimen. The results are discussed for coated printed circuit boards.
Novel criteria for overload management in power transformers
Authors: Arri E. , Mocci F. , Tosi M.
Published: July 2010

In this paper some new strategies for protecting power transformers, based on the possibility of taking measurements on machines in real operating conditions, are discussed. Earlier works showed that it was possible to determine on‐line power losses of transformers. Here the conditions that permit to separate the measured power losses into core and copper losses are defined more in detail and the possibility of incorporating these measurement techniques into a load management system, in which the real‐time transformer temperatures can be rapidly predicted, is discussed. The direct measurement of on‐line transformer losses makes it possible to achieve thermal protection of power transformers with novel strategies.
Analytic approximate calculation of short‐circuit electromagnetic forces in three‐phase steel enclosed arrangements
Authors: Safigianni A. , Tsanakas D.
Published: July 2010

In this paper analytic relations are given for the computation of the time‐varying short‐circuit electromagnetic forces acting on the conductors of arrangements with three‐phase steel enclosure, in the steady‐state. The basic assumptions for the development of these relations are the consideration of the conductors as filamentary and the restriction of the terms of the Fourier series, that expresses the forces, into two. From parametric investigations resulted the great accuracy of the computations with the approximate analytic relations compared to the accurate computations done by numerical methods and taking into account the conductors radius and large number of terms of the Fourier series.
Error insensitive distance protection
Authors: Opperskalski H.
Published: July 2010

This paper shows that no algorithm exists so far with an optimal behaviour to all non‐ideal input signals. Furthermore, it is not possible to combine an algorithm solving differential equations and a filtering algorithm to achieve an error insensitive behaviour. However, the combination of different algorithms results in an improved behaviour.
Apparent power ‐ a misleading quantity in the non‐sinusoidal power theory: Are all non‐sinusoidal power theories doomed to fail?
Authors: Filipski P. S.
Published: July 2010

Traditional non‐sinusoidal power theory does not reflect properly the energetic relations in non‐sinusoidal systems. To alleviate this situation several new power theories have been proposed recently. These new theories invariably rely on the definitions of the active power, the non‐sinusoidal apparent power and on the basic power equation, i. e., on the assumption that the geometric sum of all power components is equal to the apparent power. The paper points to the fact that the non‐sinusoidal apparent power is an artificial quantity without any physical meaning and that there is neither theoretical nor practical justification for the application of the basic power equation.
The p‐q theory in three‐phase systems under non‐sinusoidal conditions
Authors: Akagi H. , Nabae A.
Published: July 2010

The conventional theory of active and reactive power in single‐phase or three‐phase systems is based on an average value concept, thus making it impossible to define instantaneous active and reactive power in a real sense. On the basis of an instantaneous value concept, the authors have already proposed a new definition of instantaneous active and reactive power in three‐phase circuits for arbitrary voltage and current waveforms without any restriction. This is called the instantaneous reactive power theory or the p‐q theory, which is considered a basic theory of active power line conditioners such as reactive power compensators and active power filters for harmonic compensation.
Measurements of power and current components in unbalanced and distorted three‐phase systems
Authors: Andria G. , Salvatore L. , Savino M. , Trotta A.
Published: July 2010

The paper deals with the instantaneous power theory in three‐phase circuits by using the instantaneous time phasors of voltage and current. Particularly it is shown that the instantaneous components of the current time‐phasor in a rotating reference frame p‐q, oriented in such a way that the instantaneous voltage time‐phasor points to the p‐axis direction, represent the active and reactive currents. These components give rise to instantaneous real and imaginary powers, respectively. The spectral analysis of the above‐mentioned time‐phasors gives the harmonic symmetrical components of positive and negative sequence of voltage and current three‐phase systems. The line‐by‐line product of the voltage sequence spectrum by the complex conjugate of the current sequence spectrum gives the DC components of the instantaneous real and imaginary powers. The paper shows also that the instantaneous active and reactive currents are different from those defined on grounds of the Fryze's theory, which can be determined from the voltage and current sequence spectra.
Numerical algorithms for power measurements
Authors: Bertocco M. , Offelli C. , Petri D.
Published: July 2010

Several definitions have been proposed for the electrical power decomposition in non‐sinusoidal situations. However, when the spectral characteristics of the input signals are known, all the power components corresponding to the different definitions can be easily evaluated. The paper presents some numerical algorithms suited for the estimation of the voltage and current spectral components, by which all the power components and other interesting load parameters can be evaluated. Simulation examples related to the power decomposition proposed by Czarnecki are reported, showing the high accuracy that can be obtained with numerical algorithms.
The modern space‐phasor theory, part I: Its coherent formulation and its advantages for transient analysis of converter‐fed AC machines
Authors: Serrano‐Iribarnegaray L.
Published: July 2010

Four internal quantities plus the rotor position of a rotating electrical machine suffice in order to describe its dynamic behaviour. Starting from this fact, first the space‐phasor concept is introduced as an excellent analytical tool, the expressions of the main phasors are given (special attention is paid to the analysis and the physical interpretation of the voltage space phasor) and thereafter the formulation of the theory is carried out. It is then shown that all the transient states of a converter‐fed symmetrical machine can be represented by a very simple space‐phasor diagram, analogous to the one used for describing its steady state through time phasors. The diagram and the corresponding dynamic equations are deduced in a direct and immediate way, which is very useful for studies of electronically powered AC machines. The second part of this article will discuss in detail the reasons why the phasorial representation of transients is not possible neither in the “Generalized Machine Theory,” nor in the “Space‐Vector Theory” and will provide a comparison between these three theories.
Torque control of the doubly‐salient reluctance motor
Authors: Steiert U. , Späth H.
Published: July 2010

This paper describes an open‐loop torque control for a doubly‐salient reluctance motor. The reluctance motor is excited with current waveforms stored in a table. It is read out dependent on the reference torque, the speed and the rotor position of the drive. The currents were calculated off‐line, so that torque with little ripple is generated. The calculation is based on the interrelationship between the magnetic flux linkage, the phase current and the rotor position. A method for the measurement of this relationship is presented and the calculation of the phase currents are explained.
Mechanical reliability and strength of 110 kV post insulators under short‐circuit loading
Authors: Böhme H. , Golletz F.
Published: July 2010

Post‐type porcelain insulators are the weak points of high‐voltage switchgears in the case of short‐circuit loads. Whether a device will be damaged due to a break of a post insulator depends (to a high degree) on the strength of the post insulator as well as on the stress. The manufacturer guarantees for this strength a so‐called minimum breaking load. This means that the post insulator is able to withstand these loads during its life‐time without reduction of service. For the user it is important to know, whether the reliability is significantly reduced by the decreasing strength or the increasing stress. In this paper the problem will be investigated using the example of current‐conducting equipment, consisting of conductor, 110 kV post insulator and support.
Sensorless control of permanent‐magnet synchronous machines at arbitrary operating points using a modified “inform” flux model
Authors: Schrödl M.
Published: July 2010

A new method based on the “Inform” principle is presented enabling control of permanent‐magnet synchronous motors without speed‐ and position sensors. A special measurement procedure detects the electrical rotor angular position by using test signals generated by the inverter. The basic idea is to measure the different inductances in direct and quadrature axis due to saturation effects or construction. The sign of the magnetic flux is detected by shifting the magnetic set‐point with a certain armature current. Some possibilities of how to calculate the rotor angular position from test signals are given. Measurements using a DSP‐controlled drive verify the practical applicability of the new principle.
Contraction of bundled conductors in outdoor substations determined by the parabola model
Authors: Zeitler E.
Published: July 2010

Bundled conductors in outdoor substations contract in case of a short‐circuit. These cause a marked peak value of the tensile force, the so‐called pinch force, which may be crucial to the dimensioning of a substation. A reasonably simple, and at the same time sufficiently exact method for the calculation of the pinch force is the presented Parabola Model.
Calculation of three‐dimensional magnetic field for horseshoe electrode of vacuum interrupters
Authors: Schellekens H. , Shang W. , Lenstra K.
Published: July 2010

In this paper, the integral equation method for static magnetic fields has been implemented for a three‐dimensional (3D) problem with given current distribution and geometry of different materials. These methods are suitable for general 3D magnetic field problems. The algorithms are given to calculate the 3D magnetic field of horseshoe electrode of vacuum interrupters. Examples of calculated results of axial magnetic fields are given.
On the performance of spacer dampers in bundled conductors
Authors: Hagedorn P. , Kraus M.
Published: July 2010

In bundled conductors of overhead transmission lines spacers are used to maintain the distance between the individual conductor cables. These spacers are often provided with elastic and damping properties with the intent to damp out the mechanical vibrations due to vortex shedding in the frequency range between 10 Hz and 60 Hz. The present paper deals with a simple mechanical model of spacer dampers, which permits the study of the influence of different mechanical parameters on their damping performance. The dynamical characteristics of industrial spacer dampers determined in laboratory experiments can thus be compared to the values which are optimal from the vibrations damping point of view.
Research on the breakdown under type test of non‐pressurized paper‐insulated HVDC cables
Authors: Priaroggia P. Gazzana , Metra P. , Miramonti G.
Published: July 2010

One of the most interesting and important problems, met during the development of non‐pressurized impregnated paper cables for high voltage direct current, arose from the introduction of a long‐duration type test at thermal cycles under a DC steady voltage of twice the working voltage. DC cables manufactured according to a traditional paper insulating technique showed during the cooling phase of a thermal cycle a catastrophic fall of the dielectric strength of the order of 50 %. The reason for this fall is analysed both theoretically and experimentally and the way to overcome the obstacle is explained and discussed.
Asynchronous motor cage fault detection through electromagnetic torque measurement
Authors: Thollon F. , Grellet G. , Jammal A.
Published: July 2010

In this article a new method is presented allowing the diagnostic of bar or ring rupture of a cage of asynchronous machine. It is shown that a modelling of the asynchronous machine taking into account each bar and each portion of ring of the cage allows to consider the influence of a rupture upon the expression to the instantaneous electromagnetic torque. It has been put up an instrumentation permitting the measurement of this torque. The spectral analysis of the parameter leads to the diagnostic of a cage rupture by discriminating this fault from other faults, particularly mechanical ones. It is also observed that ruptures influence greatly the electromagnetic torque. The peak variation of the significant spectral lines is so important that it allows the detection of a first rupture without the need of a very sophisticated instrumentation.
Examination of transient phenomena in induction machines, caused by an incorrectly adjusted rotor‐time constant in a field‐orientated control system
Authors: Rapp H.
Published: July 2010

Field‐orientated control systems for induction machines are very sensitive to variations of the machine's rotor‐time constant. This paper deals with the transient phenomena occurring after each change of the machines load, if the rotor‐time constant is not adjusted correctly. After an analysis of the transient phenomena being in question, measures for diminishing them are discussed.
Inverter motor with sinusoidal starting currents ‐ a survey
Authors: Möhlenkamp G.
Published: July 2010

Inverter motors need only simple line‐ and machine‐commutated converters and have proved good performance for drives in the MW range. They cause high torque ripple, which is disturbing only at low frequencies, and require additional commutation devices under heavy start‐up conditions. The also very economic cyclo‐converters are only useful for machine frequencies up to about 40 % of line frequency. The new systems proposed here combine the advantages of both drives with two DC links only. The same circuits operate as a cy‐cloconverter at start‐up and low frequencies of the motor, and as a current‐source inverter at high speeds. The switchover possibilities from one operation mode to the other without any transient reaction are shown. The necessary expenditure compared to the conventional inverter motor is presented.
Skew leakage in induction machines
Authors: De Jong H. C. J.
Published: July 2010

Most induction motors have their rotor slots skewed, i. e. twisted away from the axial direction, with the intention to reduce harmful slot harmonic effects. As skewing affects the magnetic coupling between primary and secondary windings, also the fundamental harmonic performance is involved. The latter effect can be expressed for the wound‐rotor type by various modifications of the equivalent circuit, each of which corresponds with a pair of imaginary reference windings. The scaling law of the skew leakage reactance is discussed and compared with the scaling laws of the other leakage reactance components. For cage induction machines, special attention is paid to the omission of rotor bar insulation, its connection with the capricious character of skew leakage and its representation in the equivalent circuit.
Verification of the electromechanical transients program setpos by means of comprehensive power‐station measurements
Authors: Lund P.
Published: July 2010

Most electrical power engineers involved with the planning and designing of power station auxiliary power supply systems are faced with the problem of credibility of the electromechanical transients programs offered as supplementary aid in fulfilling their jobs. These programs contain a variety of mathematical models of electrical power system components, which can be combined to constitute the electrical system being analysed. Most simulation programs have been tested on a number of theoretical cases and the results compared to those of other similar computer programs. This is due to the general lack of‐ and difficulties in achieving ‐ field measurements of reproducible electromechanical transients in fully known power subsystems. Such field measurements of a slow busbar switching in the auxiliary system of a modern power station unit are presented and compared to the computational results obtained by simulating the incident using the SETPOS electromechanical transients program.
The use of decentralized measures of mobility of modes for feedback signal selection and optimum siting of power system stabilizers
Authors: Hamdan H. M. A. , Hamdan A. M. A.
Published: July 2010

The problem of choosing an optimum site for the power system stabilizer in a multimachine power system (MMPS) is considered. The method used is based on the concept of mobility of modes in a decentralized control system. The singular value decomposition of appropriate matrices is used as a computational tool. The minimum singular value of appropriate matrices is used as an index of controllability and observability of a given mode. The method takes into consideration the input and output matrices of the linearized state space models of MMPS. This is an advantage over methods that are based on the state matrix only. This advantage makes it possible to evaluate more signals in one site than is possible through previous methods. Two examples are used to demonstrate the effectiveness of the method.
A new approach to high‐power arc dynamics
Authors: Schötzau H. J. , Kneubühl F. K.
Published: July 2010

Up to the present the Mayr equation has been used for studies of the interaction of high‐power arcs with electrical networks. In the present study the Mayr equation is generalized with the aid of response and relaxation functions. It is demonstrated that this concept reaches far beyond the Mayr equation. Thus, the problem of small inductive currents in LCR circuits including an arc is solved comprehensively. In this context, the influence of a delayed arc response is revealed and new effects are predicted.
Generation of uncharacteristic harmonics in electrical plants with ac/dc converters
Authors: Loggini M. , Montanari G. C. , Cavallini A.
Published: July 2010

In this paper an investigation is carried out on the correlation between dissymmetry imbalances and the generation of uncharacteristic harmonics in low‐voltage electrical plants supplying A C/DC six‐pulse converters. After a general introduction, some typical cases of dissymmetries and imbalances are considered, relevant to supply voltage, line impedances, thyristor injection angles and filter capacitors, and the corresponding uncharacteristic harmonic currents derived by means of the simulation program EMTP. Moreover, evaluation of harmonics is made for various values of plant and load parameters in order to derive the behaviour of amplitude and phase of uncharacteristic harmonics in a wide range of plant conditions. The results provide clear relationship between kind and degree of dissymmetry and presence of uncharacteristic harmonics with useful indications for plant design.
Dynamic, power‐quality‐oriented approach to power theory and compensation of asymmetrical systems under non‐sinusoidal conditions
Authors: Czarnecki L. S.
Published: July 2010

Current and power equations of three‐phase circuits with unbalanced non‐linear loads supplied from asymmetrical and non‐sinusoidal voltage source are developed in the paper. It is suggested that the form of the power equations should be adjusted to the goal for which they are developed. Their form, which may be convenient for interpretation of power phenomena, may therefore differ from the one developed for studies on the supply and loading quality. Also it is shown that power properties of a circuit cannot be wholly determined in its static state. They can be determined, however, if the circuit response to the supply changes is observed. Such an observation and analysis of the circuit response are considered as a dynamic approach. It may provide a control algorithm for adaptive compensators.
Dynamic compensation of non‐active power using the fbd method ‐ basic properties demonstrated by benchmark examples
Authors: Depenbrock M. , Skudelny† H.‐Ch.
Published: July 2010

For the most general case of electrical polyphase circuits under non‐sinusoidal, unbalanced but steady‐state working conditions there are different definitions of active quantities needed for power transfer and non‐active quantities which could be compensated without changing the average power transfer. In practice normally the load is varying with time, therefore it is interesting how the definitions of power quantities can be extended to dynamic working conditions and what are the results of compensating non‐active quantities in such cases. Even if the load does not change with time after the start of a controllable compensator, the complete system is time varying. For this case it is shown how the non‐active quantities as defined within the FBD Method can be determined under dynamic conditions. For two simple circuits simulations are presented which show the dynamic performance of an ideal controllable compensator with a control scheme based on the FBD Method.
Parametric approach for power measurements under non‐sinusoidal conditions
Authors: Offelli C. , Petri D. , Zanin F. E.
Published: July 2010

The determination of the power components under non‐sinusoidal conditions has received great attention in the last years. Digital instrumentation, provided of signal processing capability, allows to accomplish this task by evaluating the voltage and current spectral characteristics, from which all the needed power components can be derived. The paper presents a parametric method, based on a proper model for the input signal, able to perform the evaluation of the spectral components on the basis of data collected during short observation interval. This characteristic enhances the tracking capability of the estimation method and is useful when time‐varying conditions must be detected.
Formulating requirements for a universally applicable power theory as control algorithm in power compensators
Authors: Depenbrock M. , Marshall D. A. , Van Wyk J. D.
Published: July 2010

Different power theories are examined, with regard to their applicability in controlling dynamic filters for non‐active power. Frequency‐domain approaches and a range of time‐domain approaches are considered, the latter being inherently more suitable for real‐time control of dynamic filters. Finally, some detailed attention is devoted to a combination of the approaches by Fryze, Buchholz and Depenbrock. This FBD‐approach leads to a general time‐domain resolution of power components in a generalized m‐wire system that can be used effectively in deriving control algorithms for dynamic filters of non‐active power.
Power theory of electric circuits: common data base of power related phenomena and properties
Authors: Czarnecki L. S.
Published: July 2010

This paper can be considered as an incentive for a cognition and discussion upon the very fundamentals of the power theory of electric circuits: what is the power theory; why there is a quest for it; what has been achieved; what still should be done. Also it is suggested that various power and current equations developed for describing power properties of electric circuits, in particular, circuits with non‐sinusoidal waveform of voltages and currents, as well as various conclusions and interpretations of power phenomena should not be considered as various power theories. They form rather a single power theory comprehended as a common data base of power related phenomena in electric circuits.
Error analysis based on the interaction between simulating charges in the csm for the electric‐field calculation of hv apparatus
Authors: Th. El‐Mohandes M. , Okubo H.
Published: July 2010

The purpose of this paper is to investigate the simulation accuracy sensitivity of electric field at each part of high‐voltage electrode which is often composed of multi‐electrode arrangements, using the charge simulation method (CSM). For the proper way of simulation, it is needed to introduce a boundary region at which the interaction between simulating charges become strong or negligible. The calculation results of estimating the simulation accuracy of electric field show distinguishable independent region even if the electrode parts are very close to each other. It is found that changing the charge arrangements in one part of the high‐voltage electrode, there is no influence to the calculation accuracy of electric field beyond this part. To improve the simulation accuracy of electric‐field calculation, the charge arrangements should be focused only to the part of electrode of interest.
Steady‐state security evaluation of electrical power systems by means of artificial neural network
Authors: Chiodo E. , Menniti D. , Testa A. , Picardi C.
Published: July 2010

An artificial‐neural‐network (ANN) application for steady‐state security evaluation of electrical power systems is presented. Such application is based upon a combined use of a multilayer back‐propagation neural network and of an opportune electrical system model, previously proposed by some of the authors. In the paper, the definition of steady‐state security and the problems arising from its on‐line evaluation are briefly recalled. Then, the ANN utilized is described with particular reference to the solutions adopted by the authors. Afterwards, some remarks on the system model utilized are reported. Finally, numerical applications on the AEP‐14 bus system are presented and the results obtained with different ANN configurations are analyzed.
Analytical expressions for current share in lightning protection systems
Authors: Orlandi A. , Piparo G. B. Lo , Mazzetti C.
Published: July 2010

In the present paper a circuit model is proposed, and validated, to simulate a Lightning Protection System (LPS) in which the distances between the down‐conductors and between the successive horizontal interconnecting rings are varied within a wide range of values. By the systematic application of the circuit model, solved by numerical methods, approximated expressions of current share functions are deduced. By means of such functions it is possible to identify how the lightning current is subdivided among the different conductors of an LPS with varying both the geometric configuration of the system and the typology of the grounding system. The share functions are validated by a series of experimental tests carried out on a real system placed on a building for its protection.
Optimal voltage/frequency control for space‐vector pwm three‐phase inverters
Authors: Lucanu M. , Neacsu D.
Published: July 2010

This paper presents an implementation algorithm of optimal space‐vector PWM in the case of conventional voltage/frequency control. The proposed command organization would radically save the memory used to store the pulse‐width constants. The controller implementation could be therefore achieved by any low‐cost microprocessor or microcontroller. The proposed method was verified by simulation.
Power‐quality improvement by static voltage booster
Authors: Quaia S. , Tosato F.
Published: July 2010

Among all the various types of possible disturbances affecting power quality in an electric supply (L e. spikes, frequency shift, harmonics etc.), the voltage dips are one of the most concerning because they can affect the regular operation of several widely diffused sensitive loads categories. Experience proves that most dips are characterized by a residual voltage at the delivery bus, where full outages (or micro‐interruptions) are only a small share. A remarkable improvement in the power‐supply quality can then be obtained by means of a cheap and simple static voltage booster (SVB), without energy storage, just able to sustain the voltage at the load bus bar during sag transients. In the paper this particular subject is investigated, trying to develop, among the various possible solutions, the most suitable SVB device to meet the target. The SVB dynamic performance has been tested by computer simulation, including the sag detection, control and firing system. In order to estimate the booster practical effectiveness in reducing the voltage sag's consequences, improving so the apparent utility power quality, the standard immunity characteristics of sensitive loads, like computers, and the SVB‐compensated voltage transients are compared and discussed.
Fast contingency evaluation method for generator outage simulation and power‐system security assessment
Authors: EL‐Emary A. , Arini Mahdi M. El , Alaily A. A. El
Published: July 2010

In order to speed up on‐line security assessment, a fast and accurate technique for on‐line generator outage simulation is presented in this paper. A linearized active power‐flow model is built up. After the generator outage, the active power of lost generator is distributed among the remaining units according to the frequency‐response characteristics (FRC) of individual units and loads taking into account the speed control actions of the unit governors. A linearized model of the automatic voltage regulator (AVR) and excitation system are used to derive the proposed steady‐state relation between the bus‐angle correction, obtained from the solution of active model using the redistributed power mismatch, and the corresponding changes in the voltage magnitudes. The quadratic power‐performance index for every generator outage is computed and the results are subsequently sorted in decreasing order according to the severity of effects. The proposed method is verified by applying it to a test system to show the ability of the proposed method to find the accurate solution and decrease in the computation time and memory storage required.
Comparison of two optimization techniques for the design of a three‐phase induction motor using three different objective functions
Authors: Faiz J. , Sharifian M. B. B.
Published: July 2010

Two optimization techniques, the simplex and Hooke‐Jeeves methods, are employed for optimum design of a 3.75 kW three‐phase induction motor. Three different objective functions, efficiency, cost and cost‐efficiency are used for this study. The obtained results are mainly compared in respect with their objective functions, but other design details have been also pointed out. Effects of stator‐ and rotor slot numbers and shape and the size of step in the search routine upon the optimum design are examined and discussed.
Comparison between finite‐element and traditional procedures for the prediction of busbar behaviour
Authors: Bottauscio O. , Chiampi M. , Chiarabaglio D. , Tartaglia M.
Published: July 2010

This paper investigates the multiconductor busbar behaviour under AC conditions with the aim of comparing the predictions of traditional circuit models with a more accurate analysis based on the electromagnetic field computation. This analysis employs a two‐dimensional finite‐element technique including eddy‐current effects. In linear systems this approach leads to a circuit model described by an impedance matrix, while, in presence of saturable media, field and circuit equations are simultaneously solved by a voltage‐driven field formulation. The paper analyses the behaviour of two different busbar systems when a short‐circuit current flows through them; the results obtained by the proposed approach are compared with those deduced according to the methods suggested by the IEC Standards and by the symmetrical components.
Analysis of fuzzy inverter control
Authors: Lin B.‐R.
Published: July 2010

Modern static UPS (uninterruptible power supply) must exhibit great stability, high transient response to load variations and high reliability. It must also be characterized by compactness, light weight, AC input harmonic current reduction, output voltage distortion reduction and low cost. A new control method for real‐time digital control of the single‐phase pulse‐width‐modulation (PWM) inverter for UPS applications is presented. An approach for combining the deadbeat control and the fuzzy logic compensator is proposed. Using the state variables measured at every sampling time, the controller calculates the inverter pulse width for the next sampling time. The fuzzy logic controller is used to compensate the voltage drop due to non‐linear loads. The proposed control scheme is verified by simulations for non‐linear load conditions, sudden load changes and system‐parameter variations.
Closed‐form solution of a three‐phase vsi feeding a three‐phase static inductive load
Authors: Abdel‐Halim I. A. M. , Hamed H. G. , Slama M. M.
Published: July 2010

In this paper, a closed‐form solution of the performance of a three‐phase voltage‐source, six‐step inverter feeding a three‐phase static inductive load is presented. Analytical expressions for the steady‐state currents of the system are derived from which the performance of the system can be investigated. Explicit formulae for the current ratings of the switching elements, whether thyristors, transistors or diodes used in the system are derived.
Theory and design of a space‐vector modulator for ac‐ac matrix converter
Authors: Neacsu D. O.
Published: July 2010

A new PWM algorithm for AC‐AC matrix converter derived by a vectorial analysis is presented. In addition to the development of the basic principles, the paper includes simulation results that confirm the validity of this analysis. This new Space‐ Vector PWM strategy can be generated on‐line in real time using a simple microprocessor software algorithm which is discussed. The resulting Space‐ Vector PWM is also representing a unified model for Space‐Vector Modulation strategies suitable for the particular situations of either voltage‐ or current‐source inverters or rectifier bridge.
A simplified real frequency independent modal transformation for overhead line switching transient computations
Authors: Papagiannis G. , Dokopoulos P.
Published: July 2010

Modal transformation technique is a common tool for transmission line transient computations. A simplified modal decomposition of overhead transmission lines, suitable for time‐domain switching (up to 105 Hz) transient computations, is proposed. By neglecting residual terms in the ZY matrix, transformation matrices are approximated as real and frequency independent. The resulting propagation constants remain unaffected from the line being transposed or not, although the existing asymmetries affect transformation matrices. The method can be extended for double circuit lines, provided they have the same configuration. Propagation characteristics, mode decoupling and travelling‐wave transmission effects have been investigated. Results are compared with those obtained from other methods in use.
Multiagent fault‐diagnosis expert system in power systems
Authors: Wang J. P. , Trécat J.
Published: July 2010

In order to solve the speed problem and shallow reasoning problem met in current research in fault diagnosis expert system, this paper presents a model based parallel fault diagnosis expert system for energy management systems (EMS). The Petri net model, which corresponds to the relationship between power system components and their protection systems, has been used for the inference in fault diagnosis. A multiagent parallel processing expert system, which is based on five transputers in Sun workstation, has been built for fault diagnosis purposes. The test results show that this expert system is not only fast but also has better performances.
A non‐linear programming approach based on quasi‐newton techniques for optimization of power systems
Authors: Lei X. , Povh D. , Kulicke B.
Published: July 2010

NETOMAC program is one of the most powerful software systems which has been widely used for the simulation of power systems. In order to solve various non‐linear optimization problems arising in power systems, an optimization algorithm based on the Quasi‐Newton Technique is presented in this paper. The algorithm that works as a special mode of the simulation program can be flexibly used to most describable non‐linear optimization problems either static or dynamic, and provides acceptable solutions under the consideration of all possible operational and security constraints. The algorithm offers substantial improvements in practical applications mainly due to adaptive scaling by heuristic considerations of the variable, handling the bound constraints directly with an efficient quadratic programming approach and using a modified augmented Lagrange multiplier method to deal with the functional constraints. The paper concludes with the three application examples for solving different optimization problems of power systems.
Critical evaluation of ansi pollution test for multi‐unit metal‐oxide surge arresters
Authors: Aradhya R. S. Shivakumara , Gururaj B. I. , Ramamoorty M.
Published: July 2010

Standardization of pollution testing of metal oxide surge arresters (MOA) is being attempted by different research groups throughout the world through field tests and laboratory investigations. The non‐uniform wet contamination method of ANSI standard C 62.11, 1987, which is reported to have good repeatability for temperature rise during laboratory tests, has been adopted by many countries including India. Also, much work is being done in some European countries on other methods. This paper gives a critical analysis of the ANSI method based on results of computer simulation studies and supporting laboratory tests. The sensitivity of the arrester element temperature rise on the atmospheric humidity during ANSI tests and possibility of representing the site severity have been established for the first time. It is concluded and suggested that to further improve the repeatability of ANSI test results, it may be desirable to stipulate a range of atmospheric humidity levels in the laboratory which may be of the order of 70 % to 80 %.
Distance protection of unsymmetrical lines
Authors: Hupfauer H. , Schegner P. , Simon R.
Published: July 2010

Technical, economical and ecological aspects lead to untransposed power lines. Full transposition schemes are often to expensive and not applicable to short poly‐circuit lines. Therefore line unsymmetry is of importance with respect to the impedance calculation and the setting of distance‐protection relays. As a consequence of line unsymmetry the short‐circuit impedance depends on the fault type and the measuring loop. As conventional distance protection is based on the model of a symmetrical line, this causes an unsharpness of the tripping area in the complex impedance plane. To avoid wrong tripping, distance‐protection relays must be set with reduced ranges. Consequently, the fault clearing time increases for extended sections at both line ends. Furthermore fault localization ‐ an additional feature of increasing importance ‐ will be as inaccurate as the measured impedance. Improvement of distance measurement by new current‐compensation methods are discussed in this paper. Extensions of the methods to mutual coupled double‐circuit lines are outlined.
Reliability evaluation of highly reliable computer control systems for energy generation, transmission and distribution
Authors: Kochs H.‐D. , Dieterle W. , Dittmar E.
Published: July 2010

The paper presents the results of an application‐based reliability study of distributed computer control systems with very high reliability demand, e.g. for supervision and control of power plants and energy distribution systems. A reliability classification scheme is presented and typical redundant control system structures are evaluated and classified due to their system reliability. Special focus is placed on assessing the influence of the communication system on total system reliability.
Performances of high‐voltage glass insulators subjected to fast transient overvoltages
Authors: Femia N. , Lupò G. , Petrarca C. , Tucci V. , Vitelli M.
Published: July 2010

Steep‐front, short‐duration voltage pulses occur in power systems as a consequence of lightning, switching of the increasingly used gas‐insulated switchgears or by electromagnetic pulses of very high amplitude. Such overvoltages characterised by very fast rise time may produce irreversible damages to the insulation of the different apparatuses of an electric power line. Test results will be presented in this paper concerning the behaviour of cap and pin‐glass insulators subjected to steep‐front overvoltages. In particular, the effect of the glass composition on the insulator performance will be analysed for both normal and anti‐fog configurations. Moreover, the dependence of the test results on the polarity of the applied voltage and the electrodes arrangement will also be discussed.
Open‐loop speed calculation in stator‐fixed reference frame
Authors: Németh‐Csóka M.
Published: July 2010

This paper presents two possible ways for calculating the speed of an induction machine without using any mechanical transducers. The proposed methods are based only on measured electrical quantities. A machine model is used where the rotor flux is calculated from the statorflux and the measured current. The generally valid forms are tested with Direct Self Control. The simulated performance of the proposed method together with the start‐up of an already rotating machine is included.
Analysis of high‐frequency PWM techniques suitable for resonant inverters
Authors: Neacsu D. O. , Alexa D.
Published: July 2010

Special Pulse‐Width‐Modulation (PWM) techniques capable of realizing true PWM operation of quasi‐resonant DC‐link inverters are presented. These techniques provide an increased value of the lowest switching time for higher carrierfrequencies. The harmonic performances are extensively studied by simulation in comparison with conventional Space‐Vector Modulation and a simple algorithm for real‐time implementation is developed.
Modelling and simulation of unsymmetrical supplied three‐phase induction motor
Authors: Zuckerberger A. , Alexandrovitz A.
Published: July 2010

A general mathematical model of a three‐phase symmetrical induction motor expressed by means of state equations with line‐to‐line voltages as input variables is presented. Such a model permits the analysis of the dynamic behaviour of the motor supplied with unsymmetrical sinusoidal or non‐sinusoidal voltage wave‐forms. Simulation programs were written by means of MATLAB/Simulink software package. The presented model was used to simulate transient behaviour of the motor with unsymmetrical supplied voltages and its operation when fed from a symmetrical source (the mains) and from a six‐step inverter. A mathematical model representing the induction motor operated with one phase disconnected was developed and simulated. Experimental results were compared with the simulated ones and good resemblance was observed.