bluuebunny/crossref_metadata_2025 huggingface dataset:
Expert system for energizing bulk power systems after a blackout
Authors: Markovic M. L.
Published: July 2010

In this paper an expert system for energizing the hydro‐dominated Austrian bulk power system after a blackout is presented. According to general restoration guidelines and operating procedures, the expert system computes the restoration schedule (as a sequence of events) for the presumed blackout (i. e. non‐available elements are defined). The restoration schedule is concluded using a discrete event simulator where all substations are modelled at element level. The dispatcher is guided by check lists to follow this restoration schedule and the switching instructions are proposed. Subsequent faults during the restoration result in a revision of the restoration schedule. This expert system has been realized with the help of the expert system tool KEE, and is in use as a stand‐alone program. Further integration within the energy management system is under way.
Shunt active filter for four wire low‐voltage systems: Theoretical operating limits and measures for performance improvement
Authors: Furga G. Superti , Tironi E. , Ubezio G.
Published: July 2010

A voltage‐source shunt active filter with a DC storage battery is presented. The circuit configuration and the overall working limits under ideal steady‐state conditions are discussed in detail. The effectiveness of this active filter for harmonic compensation, power factor improving, load balancing and power peak shaving is shown. Analytical relationships of the switching frequency and tracking capability versus voltage levels, current ripple and device parameters are given. A number of simulation results in the time domain and in the frequency domain under sinusoidal and non‐sinusoidal load current are presented. Design rules are also given.
Application of artificial neural networks to historical data analysis for short‐term electric load forecasting
Authors: Caciotta M. , Lamedica R. , Cencelli V. Orsolini , Prudenzi A. , Sforna M.
Published: July 2010

The paper illustrates two different Artificial Neural Networks (ANN) architectures for electric Short‐Term Load Forecasting (STLF). Two multi‐layer perceptron ANN using the back‐propagation learning algorithm have been implemented which provide different, although complementary, forecasting approaches (static and dynamic). In order to test the potentialities of the architectures implemented, the ANN have been applied to the Short‐Term Forecasting of Italian hourly electric load. The importance of this load (peak demands up to about 38 000 MW) requires tools for STLF which must be as more accurate and precise as possible. This fact has imposed the adoption of some algorithmic enhancements to the basic back‐propagation algorithm formulation. Since an adequate formulation of the influence exerted on hourly electric load by the main meteorological and climatic factors is not known at present, the data set used for ANN training phase has concerned only historical series of electric hourly demand. The paper illustrates the two ANN architectures as well as the computational platforms used for implementation. Finally, some results obtained from the application of the two ANN to the short‐term forecasting of Italian electric load relevant to three different weeks of the year 1993 are comparatively reported.
Approximate numerical calculation method for deriving an asymmetrical temperature distribution in a cross‐section of a gas‐blasted arc
Authors: Yokomizu Y. , Matsumura T. , Kito Y.
Published: July 2010

A new calculation method for deriving an asymmetrical temperature distribution in a cross‐section of an SF6‐gas‐blasted arc is proposed. Side‐on profiles of radiation intensities of four S+‐ion spectra observed from two directions perpendicular to each other are used as input data to determine asymmetrical distributions of emission coefficients in the cross‐section. The emission coefficient distribution of each spectral line is assumed to be represented by a product of three expressions: one corresponding to an elliptic component, the others being two polynomials that give degree of asymmetry with respect to x‐ and y‐direction. respectively. Unknown coefficients in two polynomials are numerically determined by an iteration process. From Boltzmunn plot diagram with respect to the emission coefficients of four S+‐ion spectral lines for each spatial position, the asymmetrical temperature distribution ofSFf,‐gas‐blasted arc is estimated successfully.
Overview, current trends and latest results in estimating the effects of load modelling on power‐system damping and stability
Authors: Milanovic J. V.
Published: July 2010

The paper presents the overview of load modelling for power‐system dumping and stability studies with main conclusions summarized from previous research. The attempt has been made to present a cross‐section of the most exploited existing load models together with the most important conclusions drawn from their implementation in power‐system stability programs. The current trends and latest results in the domain of damping of electromechanical oscillations in power systems are also presented. The effects of toad dynamics on damping of electromechanical oscillations were analyzed on the basis of one of generic toad models proposed in the past. The recent results further encourage investigation in this area and highlights the importance of proper load modelling.
An advisory system for optimal switching of power‐system capacitors
Authors: Saha S. , Tan O. T. , Christensen J. P.
Published: July 2010

A methodology is presented to determine the optimal sequence of capacitor switching in a power system for maintaining a desirable voltage profile over a load cycle. In the first part of the algorithm, the set point voltages of the generators are determined by a non‐linear secondary voltage controller that is emulated by a feed forward neural network. In the second part, these generator voltages constitute the starting point to determine the optimal switching of capacitors by using a dynamic program solver. The algorithm was validated on an IEEE 57 bus test system with the individual loads varying non‐uniformly between 50 % and 110% of their base values.
New approach of using evolutionary programming to reactive power planning with network contingencies
Authors: Lai L. L. , Ma J. T.
Published: July 2010

This paper proposes the use of evolutionary programming (EP) to reactive power planning (RPP). Several techniques have been developed to make EP practicable to solve a real power system problem and other practical problems. The proposed approach is described in detail for the IEEE‐30‐bus system. Simulation results, compared with those obtained by using a conventional gradient‐based optimization method, Broyden 's method, are presented to show that the present method is better for power system planning even under network contingencies. In the case of optimization of non‐continuous and non‐smooth function, EP is much better than non‐linear programming. The comprehensive simulation results show a great potential for applications ofEP in power system economical and secure operation, planning and reliability assessment.
A simple adaptive scheme for indirect field orientation of an induction motor
Authors: Branco P. J. Costa
Published: July 2010

A self‐adaptive scheme is described for automatically tracking the temperature and saturation‐dependent rotor time constant T, in indirect vector control. This method is based on a monitoring signal injected into the process. A cross‐correlation function between the monitoring signal and the speed error indicates the T, changes in direction (increase or decrease) and magnitude. The proposed identification algorithm presents unique characteristics: it does not use current or voltage sensors; it is not motor‐parameter dependent; the amplitude of the monitoring signal can be reduced but with an increase on the speed‐error sensibility to control interference in drive's performance and it works either on steady‐ and dynamic transient‐state. It will need some load to operate but this condition is satisfied in all practical cases. Tests were conducted with a 1.2 kW four‐quadrant AC drive. The adaptive indirect vector‐control was implemented in a microcomputer with the motor supplied by a voltage‐source inverter with current control using IGBT. Experimental and simulated results using this adaptive digital scheme for different loads and values of model T, (representing a detuned operation) are presented showing good performances.
Modelling of rectified polyphase salient‐pole synchronous machines: Influence of end‐winding leakages on short‐circuit operation diode current
Authors: Zouaghi T. , Barret P. , Vielpeau D. , Poloujadoff M.
Published: July 2010

An accurate modellization method of rectified polyphase salient‐pole synchronous machines is carried out in this paper. An eleven phase rectified synchronous generator is used to supply the field windings of a large hydraulic alternator. To simulate its operation it has been necessary to develop a convenient diode model and to determine accurately the magnetic linkage parameters. The results have shown that short‐circuit operation heavily depends on the shape of the field in the end‐turn windings.
Influence of dust particles on dc discharges in symmetrical air gaps
Authors: Al‐Arainy A. A.
Published: July 2010

Breakdown and corona are investigated in clean and dust‐polluted rod‐rod air gaps varying gap length, rod radius and voltage polarity. It is shown that similar to previous results under impulse voltages, dust pollution can significantly reduce the DC breakdown voltage values of such gaps which depends upon electrode radius, gap length and voltage polarity. These factors should therefore be considered prior to the design and application of air insulation in desert regions, where sand and dust storms can occur frequently. Possible mechanisms which control the observed behaviour are explained in detail.
Scaling and dimensioning of switched reluctance machines
Authors: Gu Q. S. , Stiebler M.
Published: July 2010

A scaling law applying to a geometrically analogous series of switched reluctance machines (SRM), based on two‐dimensional non‐linear field analysis is presented in the paper. It highlights the fact that both linear and saturated permeances per unit axial length at different rotor positions are invariant under scaling. Based on a normalized static energy conversion loop in the electric/magnetic loading plane a quality factor is defined which serves to calculate the average specific torque. A simple analytic expression for predicting the quality factor of a SRM is derived which depends only on the linear permeances at two extreme rotor positions and the electric and magnetic loadings at the top point of the static energy conversion loop. This simplifies greatly the prediction of specific torque at an early design stage. Finally, the effects of air‐gap dimension ratios, electric loading, magnetic gear ratio and leakage flux on the quality factor and the specific torque in designing SRM having different magnetic gear ratios are discussed.
A novel configuration for a wide‐range high‐power fiber‐optic current sensor
Authors: Irace A. , Breglio G. , Luciano A. , Zeni L. , Cutolo A.
Published: July 2010

In this paper it is discussed a new configuration for a fiber‐optic current sensor (FOCS) which increases the linearity range of the device without decreasing its sensitivity exploiting an appropriate feedback loop; in this way the whole system behaves as a “null‐detector”. Moreover, the effect of bending‐induced linear birefringence is explicitly taken into account in the design and optimization of the sensor. It is shown that the response of the experimental apparatus is practically temperature independent and that its bandwidth gets values higher than I MHz.
Feedforward torque control of a switched reluctance motor based on static measurements
Authors: Bausch H. , Kanelis K.
Published: July 2010

A model of the non‐linear switched reluctance motor (SRM) has been developed that provides an analytical representation based on static measurements of the flux linkage by simple polynomial functions. Using an approximation of the Φ(i)‐characteristic with the rotor position angle γ as parameter it is possible to calculate the dynamic performance of the drive in the whole torque‐speed range. Depending on the torque command Tw the switching angles γO (“on”) and γc (“off”) are determined with minimum ohmic losses under the assumption of a constant supply voltage. For the ease of demonstration the results are restricted to the field weakening range. It turns out that the switching angles are parabolic functions of the torque with the well‐known tendency for advance‐shifting at increasing speed. The calculated current waveforms and average torque values coincide well with those measured at the test drive.
The real confidence intervals in state estimation
Authors: Al‐atwan A. , Koglin H.‐J.
Published: July 2010

The computation of the confidence intervals has been proposed in this paper. Two methods are developed for this purpose. In the first method the confidence intervals are evaluated by calculating the variance of the estimation errors, the differences between the true and the estimated values. While in the second method, the confidence intervals are evaluated depending on the up‐to‐date results of the state estimation. Both methods are tested using a measuring system for the IEEE‐14‐Bus‐Test‐Network with the aid of the Monte‐Carlo‐Simulation‐Technique.
Description of power electronic circuits by block diagrams
Authors: Tuttas C.
Published: July 2010

Power electronic circuits are non‐linear dynamic systems. Until now, it is not usual to describe these systems by block diagrams. In this paper a new model for power electronic switches is proposed. The semiconductor devices are represented by voltage and current sources. Due to this modelling block diagrams of power electronic circuits can be drawn. These block diagrams give an insight into the dynamic behaviour of power electronic systems.
Damping of common‐mode torsional oscillations using a modified NGH SSR damping scheme
Authors: Wang L.
Published: July 2010

This paper presents the analyzed results on the application of a modified NGH SSR damping scheme for damping common‐mode torsional oscillations that occur in a power systems containing series‐capacitor compensation. The IEEE Second Benchmark Model, system‐2, which has two non‐identical turbine‐generator sets connected to an infinite bus through a series‐capacitor compensated transmission line, is employed to investigate the possible unstable subsynchronous resonance (SSR) which can be suppressed by the proposed damping scheme. A unified approach based on modal control theory is employed to design damping controllers for the modified NGH SSR damping module. Frequency‐domain approach based on eigenvalue analyses such as different operating conditions and stable regions on RE‐Xc plane is performed. Time‐domain approach based on non‐linear model simulations under a severe three‐phase short‐circuit fault at infinite bus is also carried out. It can be concluded from the simulation results that the proposed modified NGH SSR damping scheme incorporated with the designed damping controllers can effectively suppress the common‐mode torsional oscillations.
400‐kV‐network harmonic impedance evaluation from harmonic distortion measurements at the RFX site
Authors: Bettini P. , De Lorenzi A.
Published: July 2010

The lack of knowledge of the harmonic frequency behaviour of the extra‐high‐voltage (EHV) transmission network prevents the possibility to choose, at the design stage, an appropriate system for harmonic mitigation for current harmonic source loads directly fed by the transmission network, as well as arc furnaces and facilities for thermonuclear fusion researches. The paper describes the methodology employed to determine the harmonic network impedance from current and voltage measurement seen at the Camin‐Padova node of the Italian transmission network, in which are injected the current harmonics produced by the reversed field pinch experiment (RFX) fusion facility; in particular, a simple method for precise measurement of voltage harmonics is presented in detail.
Proposal of a new method for controlling the torque and the flux of a voltage source inverter‐fed induction motor
Authors: Amin B.
Published: July 2010

In this paper, a method for controlling the torque and the flux of an induction motor is presented. It consists in calculating, within each time‐step, appropriate values of the voltage to be impressed across the phase windings. The method takes into account the effects of the magnetic saturation, as well as those of the variations of the rotor and stator resistances versus the temperature. It does not require any integrators for evaluating the stator‐flux and works under controlled commutation frequencies.
Electrode‐fall voltages of SF6 and air arcs between electrodes of Fe, W, Cu‐W, Cu and Ti in the current range from 10 A to 20 kA
Authors: Yokomizu Y. , Matsumura T. , Henmi R. , Kito Y.
Published: July 2010

Measurements were made of the sum of cathode‐fall and anode‐fall voltages, i .e. electrode‐fall voltage Ufall for SF6 and air arcs at a pressure of 0. 1 MPa in a wide current range from 10 A to 20 kA. The arcs were burned between electrodes of iron, tungsten, copper‐tungsten, copper and titanium. For each electrode, Ufall atagiven current was estimated as the arc voltage at the zero gap length between the electrodes, which was extrapolated from arc voltages measured in short gaps with lengths below 3 mm. The electrode‐fall voltage Ufall of the SF6 arc proved to be 17.5 V, 13.8 V, 17.5 V, 17.5 V and 17.3 V for the Fe, W, Cu‐W, Cu and Ti electrodes, respectively. The electrode‐fall voltage Ufall was affected by the electrode material, while Ufa u of the air arc is almost the same as that of the SF6 arc. It was also found that Ufall of each arc at a given electrode was independent of current in the above range.
Procedures for quality pattern diagnosis
Authors: Schilling M. Th.
Published: July 2010

This paper addresses the problem related with the investigation of power systems monitoring procedures and establishment of statistical performance criteria. For the sake of illustration, the application of some criteria to an existing large scale subtransmission system is described, and analyzed.
Active power filter for harmonic and reactive power compensation in three‐phase, four‐wire systems supplying non‐linear loads
Authors: Singh B. , Ai‐Haddad K. , Chandra A.
Published: July 2010

An active power filter (APF) is proposed which eliminates harmonics, compensates reactive power and neutral current in a three‐phase four‐wire electric system supplying non‐linear loads. An insulated‐gate‐bipolar‐transistor (IGBT)‐basedpulse‐width modulation (PWM) voltage source inverter (VSI) with a DC bus capacitor is employed as an APF. A hysteresis‐rule‐based carrierless PWM current control technique is used to generate switching signals to the devices of the APF. Three single‐phase diode rectifiers supplying resistive‐capacitive loads are considered as a three‐phase non‐linear load. A detailed dynamic model of the scheme is developed to study transient and steady‐state behaviour of the APF. The proposed APF is found capable to compensate reactive power, neutral currents and to reduce the harmonics below specific recommendations of IEEE‐519 standard.
Complete symbolic factorization for the security analysis of power systems
Authors: Berizzi A. , Piovan U. , Silvestri A. , Zaninelli D. , Pavani R.
Published: July 2010

In modern power systems, it is more and more important to assess in a very short time the security of the system, checking the ability of the network to sustain possible contingencies. The paper presents a symbolic approach to an efficient implementation of the factorization, applied to the well‐known Cholesky factorization, that turns out to be useful especially when there is the need to factorize several matrices with the same sparsity structure, as in case of security studies.
New approach to the calculation of electrical transients, Part I: Theory
Authors: Bijl N. , Van Sluis L. Der
Published: July 2010

The calculation of electrical transients in power systems is important for insulation coordination. Most of the compiiter programs in current use are based on the nodal admittance method. This paper describes a computer program for the calculation of electrical transients based on a new approach which enables the use of more sophisticated numerical integration routines. The program can cope with linear network elements like resistors, capacitors, reactors, voltage and current sources and also with non‐linear network elements like surge arresters and arc models. The description of the models and their parameters is stored in libraries separate from the main program. The user can define his own models.
Definitions of electrical quantities commonly used in non‐sinusoidal conditions
Authors: Ferrero A.
Published: July 2010

The analysis of electrical systems under non‐sinusoidal conditions has become an important topic in electrical engineering. Most of the approaches to the analysis and operation of electrical systems are undergoing a thorough revision, and several contributions concerning these topics can be found in the recent literature. However, in the development of this matter problems occur because of misunderstanding and misinterpretation mainly due to the terminology used by individual authors when referring to identical concepts and quantities. The present contribution considers the definitions of quantities that are frequently used for the analysis of non‐sinusoidal systems and formulates a technical‐scientifically sound document where these quantities and concepts are defined, a technical sound name is given, and a symbol is proposed for each quantity.
Hyper space vectors: A new four‐quantity extension of space‐vector theory
Authors: Depenbrock M. , Staudt V.
Published: July 2010

The space‐vector theory, which allows to describe three linearly dependent quantities (e. g. three voltages or three currents) using only two linearly independent quantities represented in an orthonormal coordinate system, is widely used in the fields of AC machine theory, power definitions and active filtering. It can be used very effectively in case of circuits with only three terminals. Problems occur in case of four terminals, when four linearly dependent quantities (e. g. four currents, the sum of which is always zero) exist. In this case a zero‐sequence quantity can be additionally introduced, which has to be treated separately with special equations. Vector operations like cross product or dot product, which are very useful to calculate e. g. power quantities, can no longer be used in the general case. This paper presents a method transforming any system represented by four linearly dependent quantities or by three linearly independent quantities into a three‐dimensional orthonormal coordinate system. All four members of a set of linearly dependent quantities are treated equally. We suggest to call this representation Hyper Space Vector (HSV). A lot of vector operations can be applied without problems to HSV, making calculations much easier and more graphic.
Assessment of electric power quality: Indices for identifying disturbing loads
Authors: Muscas C.
Published: July 2010

The study aimed at defining parameters capable of assessing, in terms of distortion and unbalance, the quality of the electric power drawn by the customer. Taking as a starting point the advantages and limitations of the methods proposed so far in the literature, two new indices are introduced, useful for quantifying the disturbing characteristics of a load. The efficiency of these indices has been assessed by computer simulations to assess the applicability of the method to three‐wire and four‐wire three‐phase systems in many realistic situations.
Synthesis of pseudo‐balanced three‐phase line configurations
Authors: Faria J. A. Brandāo
Published: July 2010

In analysing lossy three‐phase line overhead configurations it is commonly believed that the well‐known example of a perfectly transposed line is the only and single example of a balanced configuration. It is shown that this is a mistake. Conditions are established and a procedure is developed for synthesizing balanced un‐transposed line configurations. Concrete examples illustrating such configurations are presented.
Harmonic blocking compensator: Frequency properties
Authors: Hsu S.‐M. , Czarneeki L. S.
Published: July 2010

Resonant harmonic filters (RHF) commonly used for reducing waveform distortion in distribution systems have a number of disadvantages. Their effectiveness degrades with an increase in the distortion of the distribution voltage. The current harmonics other than those to which the filter is tuned can be amplified. Filter performance is very sensitive, usually, to reconfigurations in the distribution system. Active harmonic filters are alternative for RHF. They have high complexity, however, and their dissemination in distribution systems seems to be rather slow. This paper investigates another alternative for RHF, namely a harmonic blocking compensator (HBC) built of a shunt capacitor and a series resonant link tuned to the fundamental frequency. This paper compares properties of RHF and HBC, provides fundamentals for the design of HBC and illustrates their properties with results obtained with a laboratory prototype.
System impedances and background noise in the frequency range 2 kHz to 9 kHz
Authors: Gretsch R. , Neubauer M.
Published: July 2010

A one year research effort was launched to investigate the internal impedances and coupling impedances within the public low‐voltage network in the frequency range from 2 kHz to 9 kHz. At 250 different nodes, roughly 6000 impedance measurements were carried out. In this paper, the measurement method and the equipment used are described and a new “wireless” method for measuring coupling impedances between distant nodes is presented. The most important results of the measurements are also summarized.
Design aspects of hybrid compensation systems
Authors: Mattavelli P. , Tenti P.
Published: July 2010

The paper focuses on theoretical design considerations of hybrid compensation systems, which include tuned L‐C filters, thyristor‐controlled reactors (TCR) and thyristor‐switched capacitors (TSC). The approach derives from optimum compensation technique employing parallel configuration of reactors and capacitors, where purely capacitive compensation is substituted by L‐C branches. This solution, recommended for distorted systems, allows a decomposition of the load currents in terms which are not strongly dependent of the source impedance. The method is also applied to the design of multiple tuned L‐C filters, taking into account load current harmonics and the effect of the supply impedance.
Methods of condition monitoring and fault diagnosis for induction motors
Authors: Thorsen O. V. , Dalva M.
Published: July 2010

The study gives a synopsis over condition monitoring methods both as a diagnostic tool and as a technique for failure identification in high‐voltage induction motors. Methods of fault detection are reviewed and analyzed: mechanical (vibrations, shock pulses, acoustic, speed fluctuations), electro‐mechanical (currents, surges, partial discharges, leakage fluxes) and temperature‐, oil particle‐, gas analysis, and performance‐ and visual methods. The study indicates how different types of faults generate different frequency components in vibration spectra, in motor supply current, in torque and in magnetic field, and relationships between fault types and spectra have been developed. Supply current waveform analysis has been applied to demonstrate the detection of broken rotor bars and bearing faults.
Resonant DC‐AC converter with low ripple output voltage
Authors: Alexa D. , Ionescu F. , Neacsu D. O. , Radomirescu B.
Published: July 2010

The paper introduces a new resonant DC link inverter that allows PWM capability and lower overvoltages on the load voltage. This is provided by keeping the clamping capacitor at a constant voltage, while the resonant circuit is continuously operated. Both DC link and inverter output present pulses with low magnitude. The new resonant circuit has the following main advantages: a more precise control of the pulse widths of the load voltage and the resonant circuits elements are less stressed since the current load of these elements is smaller. The design hints are also given.
Experimental investigation of grounding grid impulse characteristics
Authors: Stojković Z. , Savić M. S. , Nahman J. M. , Salamon D. , Bukorović B.
Published: July 2010

The paper provides a procedure for experimental determination of the grounding grid impulse characteristics. The principles of forming the measuring scheme, disposition and characteristics of the equipment used are described. Some of the numerous experimental results for the square‐shaped grounding grid are presented. The results have been obtained for various shapes, magnitudes and discharge points of the impulse currents and are related to the cases without soil ionization around the grid elements.
Cost‐benefit evaluation of voltage conditioners installation in industrial and commercial power systems
Authors: Quaia S. , Tosato F.
Published: July 2010

In industrial and commercial sectors, loads are becoming increasingly sensitive to brief supply voltage disturbances. As a consequence, today voltage dips have more impact than just a few years ago. Fast voltage conditioners, improving the load immunity characteristics and accordingly reducing the expected number of load interruptions or malfunctions due to supply voltage dips, can allow large cost savings. Different categories of voltage conditioners are existing today, ranging from energy‐stored devices (like uninterruptible power supply) to no energy‐stored devices (like static voltage booster). To reduce the effects of supply voltage dips on a given plant, usually several different possible arrangements must be investigated, depending on the conditioners type, size and bus location. To determine the optimal arrangement is not always immediate. A methodology based on the minimum revenue requirement (MRR) is proposed in the paper, and a numerical example is given as well.
Effect of earth stratification on impedances of power transmission lines
Authors: Moghram I. S.
Published: July 2010

Accurate prediction of ground fault currents in above ground transmission systems requires that the earth be modelled using accurate representation. Traditionally, the earth is modelled as a homogeneous half space of unit permeability. In practice, the earth is composed of strata of various resistivities and permeabilities. Equations developed for multi‐layered earth model using the double integral transform techniques are presented in this paper. Results for two‐ and three‐layered earth demonstrate that the zero‐sequence resistance and the zero‐sequence reactance are considerably affected by characteristics of earth stratification. The presented equations can be used to aid electrical engineers in predicting AC fault currents more accurately.
On the realizability of balanced untransposed overhead line configurations
Authors: Faria J. A. Brandāo
Published: July 2010

A procedure for synthesizing balanced untransposed overhead three‐phase line configurations has been recently presented. However, such a procedure is based on the simplifying assumption that the soil influence can be described by an impedance matrix with all elements equal. In the present paper we abandon that assumption and model the earth effect via the Dubanton 's approach. In the frame of this more accurate model we show that the realizability of such untransposed balanced line configurations cannot indeed be assured, not even in the low‐frequency and high‐frequency limiting cases.
DSP‐based implementation of an improved control algorithm of a three‐phase active filter for compensation of unbalanced non‐linear loads
Authors: Singh B. , Singh B. N. , Chandra A. , Al‐Haddad K.
Published: July 2010

This paper deals with an implementation of a new control algorithm/or a three‐phase active filter (AF) to eliminate harmonics, compensate reactive power and to balance unbalanced non‐linear loads. An insulated‐gate‐bipolar transistor (IGBT)‐based current‐controlled pulse‐width modulated (PWM) voltage‐source inverter (VSI) with a DC‐bus capacitor is used as an AF. The reference supply currents are derived in phase with supply voltages using a sliding mode controller (SMC) over DC‐bus voltage of the AF.A digital signal processor (DSP) is used to implement the control algorithm of the AF. An indirect PWM current control over the reference and sensed supply currents is implemented for generating the gate signals for IGBT of the AF. Test results of the proposed AF are given to demonstrate the harmonic elimination, reactive power compensation and load‐balancing capabilities of the AF.
Steady‐state power flow and voltage control by unified power‐flow controllers, part 1: Modelling and algorithms
Authors: Song Y. H. , Liu J. Y.
Published: July 2010

The unified power‐flow controller (UPFC), with its unique combination of fast shunt and series compensation, offers a versatile device for the relief of transmission constraints. However, in order to realise this potential benefit, appropriate local and global power‐system control strategies must first be developed. UPFC steady‐state model and its implementation in normal (open‐loop) power flow has been investigated by a number of investigators. This paper further develops the power‐injection method based on optimal multiplier power flow for the steady‐state control of UPFC for power‐flow control and voltage support. The proposed power injection power‐flow control can be effectively used to derive UPFC control parameters to achieve the required control objectives.
Steady‐state power flow and voltage control by unified power‐flow controllers, part 2: Applications
Authors: Song Y. H. , Liu J. Y.
Published: July 2010

The unifiedpower‐flowcontroller(UPFC) isa powerfuldeviceforthe reliejroj'transmission constraints. Part 1 of the paper proposes novel steady‐state modelling and control algorithms for the study of UPFC, which use power‐injection models to derive control parameters for UPFC to achieve the required line active power control and bus‐voltage support. The proposed method does not change the symmetrical structures of Jacobian matrix, avoids the initialisations of control parameters and can cover a wide control range of UPFC due to the characteristics of optimal multiplier power‐flow algorithms employed. This paper describes in detail the applications of the proposed theory in a 28‐node system. The convergence of controlled power flow is analysed. Control performance has been evaluated. The numerical results presented clearly illustrate the effectiveness of the proposed approach.
Correction of resistance measurement of large grounding systems
Authors: Berberović S. , Boras V.
Published: July 2010

A method for the systematic error correction which appears at the grounding system resistance measurement by means of an auxiliary current electrode, when the distance between the edge of the grounding system and the center of the current electrode is shorter than the minimum distance required by the standard, is presented in this paper. The systematic error increases with the ratio of the size of the grounding system to its distance from the current electrode. The method for the correction of the systematic error is based on modelling of grounding system and current electrode by hemispheres in uniform and two‐layer soil model. The calculation results are presented by diagrams, which are useful for the evaluation of systematic error.
Evolutionary programming‐based economic dispatch for units with multiple fuel options
Authors: Jayabarathi T. , Sadasivam G.
Published: July 2010

This paper presents the application of evolutionary programming (EP) to economic dispatch of generators having piecewise quadratic cost functions. The proposed EP algorithm always determines the global or near global optimum without any restrictions on the shape of the cost functions. The method is applied to an example system with piecewise cost functions and the results are compared with those of the recent adaptive Hopfield neural network method. The test results prove that the EP method is simpler and more efficient for solving economic dispatch (ED) problems with multiple cost curves than many existing techniques.
Monitoring the quality of SF6 in gas insulated S witchgear using ion mobility spectrometry
Authors: Soppart O. , Baumbach J. I. , Trindade E. , Alberti S. M. , e Silva J. M. Moraes , Klockow D. , Peier D.
Published: July 2010

Despite of the high reliability of modern gas insulated switchgear and substations, failures still occur in their long term operation. Partial discharge measurements are useful to test the reliability of the insulating system. A refined technique, however, for rapid on‐site quality control of the insulating gas inside the equipment is still missing. For this purpose, ion mobility spectrometry is proposed, that combines relatively low cost equipment and operation with high sensitivity and rapid data acquisition. A portable ion mobility spectrometer specially designed for measurements in SF6 is presented. First results obtained from on‐site measurements in a gas insulated substation are presented and compared with supporting investigations carried out in the laboratory using SF6 artificially aged in a discharge chamber. The employment of an ion mobility spectrometer for continuous on‐line control ofSF6 is proposed in order to help to reduce the costs for service and maintenance and lead to an even higher reliability of electrical power distribution.
Analysing subsynchronous resonance phenomena in the time‐ and frequency domain
Authors: Lei X. , Buchholz B. , Povh D.
Published: July 2010

Subsynchronous resonance (SSR) is a condition that can exist in a power system, especially for long‐distance transmission systems with series compensated line. It can cause shaft fatigue and possible damage or failure of the generator involved. The analysis of the SSR phenomenon can be performed usually by using three individual analytical methods ‐frequency scanning, eigenvalue analysis in the frequency domain and transient torque analysis in the time domain. In this paper the comprehensive simulation program NETOMAC with a complete solution for analysing SSR is presented. Based on a common data set of the system concerned, both frequency and transient torque analysis can be performed, taking interactions among the spring‐mass system of the turbine‐generator units and the electrical network into consideration. Two case studies are demonstrated in the paper. The results achieved validate the functionality of the program for SSR analysis.
Electromagnetic torque of a synchronous machine during a single out‐of‐phase reclosing
Authors: Ammari A. C. , Pierrat L.
Published: July 2010

The adoption of single‐pole switching for a radial transmission line which connects large synchronous machines to the power system would submit these machines to repetitive mechanical stress. To evaluate the total mechanical stress, it is first necessary to determine the electromagnetic torque and to evaluate its transient maximum values at reclosing. In this paper, maximum values of the electromagnetic transient torque at single‐pole reclosing are first computed using a simplified analytical approach. The analytical results are then validated by numerical simulations and by an experimental test on a laboratory synchronous machine. It will be shown that single‐pole reclosing would be, in the worst case, as restricting as three out‐of‐phase synchronisation.
Application of clarke's transformation to the modal analysis of asymmetrical single‐circuit three‐phase line configurations
Authors: Faria J. A. Brandāo
Published: July 2010

This paper addresses three interrelated topics concerning the modal analysis of asymmetrical single‐circuit three‐phase transmission lines. The subject of the study is a three‐phase overhead line whose set of conductors lie on a plane arbitrarily tilted with respect to the ground surface. Varying the angle of tilt from zero to ninety degrees transforms a flat line into a vertical line configuration. The first topic discussed is the dependence of the exact modal parameters (attenuation, phase velocity, eigenvectors) on the tilt angle measuring the line asymmetry degree. The second topic deals with the well‐known Clarke transformation which can be used to successfully diagonalize ZY matrices other than those describing balanced lines. The third topic refers to the computation of approximate modal parameters for the asymmetrical tilted line, using a very simple perturbation theory approach based on the Clarke transformation. Illustrative computation results reveal that the exact and the approximate modal parameters match well, although errors tend to increase with increasing line asymmetry.
About the role of the park imaginary power on the three‐phase line voltage drop
Authors: Ferrero A. , Leva S. , Morando A. P.
Published: July 2010

In this paper the line voltage drop concept is investigated and extended to non‐sinusoidal conditions. The results are applied to the three‐phase configuration. In this approach the presence of harmonic and sequence components is taken into account. The formal invariance of the obtained results with respect to the original single‐phase relationships is ensured by means of the three‐phase rms concept. The Park transformation is used as well, so that the three‐phase relationships are reduced to a simpler formal single‐phase approach: the simultaneous contributions of harmonic and sequence components are unified in a single formulation. Therefore the Park imaginary power role results as a natural extension of the usual single‐phase reactive power concept.
Position‐sensorless direct‐torque‐controlled synchronous motor drive for ship propulsion
Authors: Niemelä M. , Luukko J. , Pyrhönen J. , Pyrhönen O. , Kaukonen J.
Published: July 2010

A new concept is proposedfor position‐sensorless Direct‐Torque‐Controlled (DTC) synchronous motor drives for ship propulsion. The principles of determination of the initial rotor position at standstill or the position of a rotating rotor, the operation at zero speed and at low rotational speeds in general are described. The study introduces also a flux linkage estimate correction method for the DTC. Some of the results of the numerous experiments performed with a laboratory prototype drive are given.
Fully biodegradable polymeric micelles based on hydrophobic‐ and hydrophilic‐functionalized poly(lactide) block copolymers
Authors: Nottelet Benjamin , Di Tommaso Claudia , Mondon Karine , Gurny Robert , Möller Michael
Published: July 2010

Novel amphiphilic diblock copolymers from a combination of hydrophobic‐functional poly(lactides) (PLAs) with hydrophilic‐functional PLAs or poly(malic acid), respectively, toward fully biodegradable materials for medical applications, such as micellar drug delivery systems, are reported for the first time. The presented PLA‐based polymeric micelles are characterized by their small size below 100 nm, low critical micellar concentrations, good in vitro stabilities at room and body temperature, and efficient incorporation capability of hydrophobic compounds, particularly with regard to potential drug substances. Moreover, the advantage of being totally degradable with different rates at different pH values, as investigated in medical cancer treatment, is demonstrated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3244–3254, 2010
Facile syntheses, morphologies, and optical absorptions of P3HT coil‐rod‐coil triblock copolymers
Authors: Lim Herman , Huang Kuo‐Tung , Su Wei‐Fang , Chao Chi‐Yang
Published: July 2010

Here we report syntheses, photophysical properties, and morphologies of a series of coil‐rod‐coil ABA triblock copolymers containing highly regioregular poly(3‐hexylthiophene) (P3HT) as the central rod block. A new methodology, based on the coupling reaction between living polymeric anions [polystyrene, polyisoprene, and poly(methyl methacrylate)] and aldehyde terminated P3HT, was successfully developed to synthesize the triblock copolymers with low polydispersities. This coupling reaction was effective for building blocks with a variety of molecular weights; therefore, a good variation in compositions of the triblock copolymers could be feasibly achieved. The non‐P3HT coil segments and the solvents were found to exhibit noticeable effects on morphologies of the spin‐coated thin films. Attachment of the coil segments to P3HT did not change the optical absorption of the P3HT segment as the block copolymers were dissolved in solution regardless the chemical structure and the molecular weight of the coil segment. Interestingly, different UV–vis absorption behaviors were observed for the spin‐coated thin films of the block copolymers, which closely related to their morphologies. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3311–3322, 2010
Miktoarm star copolymers via combination of RAFT arm‐first technique and aldehyde–aminooxy click reaction
Authors: Wu Zhao‐Mian , Liang Hui , Lu Jiang , Deng Wen‐Li
Published: July 2010

A facile synthetic pathway to miktoarm star copolymers with multiple arms has been developed by combining reversible addition–fragmentation chain transfer (RAFT) arm‐first technique and aldehyde–aminooxy “click” coupling reaction. Star polystyrene (PS) with aldehyde functionalized core was initially prepared by RAFT arm‐first technique via crosslinking of the preformed linear macro‐RAFT agents using a newly designed aldehyde‐containing divinyl compound 6,6′‐(ethane‐1,2‐diylbis(oxy))bis(3‐vinylbenzaldehyde) (EVBA). It was then used as a multifunctional coupling agent for the subsequent formation of the second generation poly(ethylene glycol) (PEG) arms via the click coupling reaction between its aldehyde groups and aminooxy‐terminated PEGs. The possible formation of PS‐PEG miktoarm star copolymer with Janus‐like segregated structure in cyclohexanone was also investigated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3323–3330, 2010
Stereoisomeric effects in thermo‐remendable polymer networks based on Diels–Alder crosslink reactions
Authors: Canadell Judit , Fischer Hartmut , De With Gijsbertus , van Benthem Rolf A. T. M.
Published: July 2010

This study describes the synthesis, the spectroscopic, and the thermal characterization of linear and crosslinked polymers as well as a number of corresponding model compounds, containing Diels–Alder adducts derived from furan and maleimide groups. The thermal reversibility (rDA, DA) of structurally varied model compounds, polymeric and network structures were studied by differential scanning calorimetry, where possible in combination with 1H NMR spectroscopy. It was established that the endo and exo DA stereoisomers show significantly different thermal responses: the rDA of the endo DA‐adducts typically takes place at 20–40 K lower temperatures than that of the corresponding exo DA‐adducts in all cases, with the exception of some aromatic maleimides. Although in situ isomerization was observed to a limited extent and only in some cases, this effect is not expected to influence the thermoremendability of DA‐crosslinked networks being dependent on two separate stereoisomeric rDA steps. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3456–3467, 2010