bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydraulically coupled power‐plants commitment within short‐term operation planning in mixed hydro‐thermal power systems
Authors: Rakic M. V. , Markovic Z. M. 
Published: July 2010

AbstractA new method for short‐term operation planning and power exchange scheduling of interconnected hydro‐thermal power systems is proposed in the paper. The criterion function is the total variable profit obtained by sales of energy to customers within the system, exchange of energy with other systems, diminished by the cost of system operation. The method is based on Lagrangian relaxation, decomposition technique and successive solution of dual and primal problems. The dual and primal problems are decomposed and solved using appropriate optimization methods, while Lagrangian multipliers are corrected using subgradient method. Dual hydro subproblems are solved using linearization and network flow method. Special modification of the algorithm is made so as to enable commitment of hydro power plants, taking into account bilogical constraints on minimal flow of water downstream of the hydro power plant. The efficiency of the method is illustrated on a test problem.
Computer‐aided design of magnetostrictive devices using terfenol‐D
Authors: Benbouzid M. E. H. , Spornic S. A. , Body C. 
Published: July 2010

AbstractThis paper describes a model for the non‐linear magnetomechanical coupling in new highly magnetostrictive materials. This model is devoted to the Computer‐Aided Design of magnetostrictive devices. It is based on an iterative process of successive magnetic and mechanical computations by a the Finite Element Method. Magnetic and mechanical quantities are still coupled by the iterative process. As a matter of fact, the use of experimental data through the Surface Spline Method allows the introduction of the magnetomechanical coupling. The experimental data are collected from a specially designed sample holder devoted to the static characterization of Terfenol‐D rods. Comparisons between numerical outputs from the model and the experimental data reveal that the model is quite powerful to describe the magnetomechanical coupling in highly magnetostrictive materials as Terfenol‐D. Otherwise, the proposed model has been extended to take into account the magnetostrictive effect in microsystems using highly magnetostrictive thin films. Numerical computations provide in this case coherent results and show that it is able to describe the global behaviour of highly magnetostrictive microsystems.
Simulation of complex‐valued, frequency‐dependent quantities in transients programs
Authors: Heimbach M. 
Published: July 2010

AbstractTransients analysis in power systems requires for many applications an effective and accurate simulation of complex‐valued, frequency‐dependent quantities, e. g. the simulation of grounding structures. The objective of this paper is to give methods to represent complex‐valued, frequency‐dependent quantities by adequate functions and strategies to incorporate them in transients programs. This shall be done in a general manner, without focusing on a specific application. Due to the fact, that transients programs work in the time domain, methods performing the transformation from the frequency into the time domain during the run‐time simulation are mandatory. The methodology to fit the frequency response by means of rational functions is well known. In the first part methods to incorporate rational functions into transients programs are briefly introduced. In the second part three different approaches to determine accurate approximations of complex‐valued, frequency‐dependent quantities are presented. Afterwards the different strategies are tested and discussed with regard to different applications. Finally, the incorporation is validated by comparison to Fast Fourier Transform (FFT).
Probabilistic model and contacts reliability estimation method of electromagnetic AC contactors
Authors: Wróblewski Z. 
Published: July 2010

AbstractIn the paper a probabilistic reliability model of contacts used in low voltage AC electromagnetic contactors is presented along with the theoretical foundation of the contacts reliability estimation method which employs resulrs of the simplified conracts durability tests. The model is derived from the analysis ofphysical and chem‐ ical processes which are observed during contactor operation and may result in contacts failure. The clue of the model is the mathematical description of the contacts wear allowance deterioration which is considered as the forecasting parameter of contacts durability. The model presented appears to be more adequate and accurate than the other ones which are used for description of contacts wear‐off mechanisms. Both the model and the method proposed can be applied in analysis of influence of material and design parameters on contacts durability, in design of new contacts and arc extinguishing chambers and, first of all, in the development of new and fast durability tests which can be applied by contactor manufacturers and users.
Investigation of the transient behaviour of a superconducting magnetic energy storage (SMES) generating high power pulses
Authors: Miri A. M. , Sihler C. , Salbert H. , Vollmer K.‐U. 
Published: July 2010

AbstractA method for calculating transient voltages in superconducting magnets has been developed. The prediction of over voltages is an essential requirement in avoiding insulation damages in expensive high‐power magnets. A single coil of a modular built Superconducting Magnet Energy Storage (SMES) was modelled as a strongly coupled R‐L‐C network with 8556 mutual inductances. The calculated transient behaviour of the model corresponds well to the measured unit function response of the investigated coil. The coil was designed with respect to the fast repetitive ramping of the SMES. Resonant oscillations are well damped by the mixed matrix Cu/CuNi/NbTi wire used. Due to the high safety margin of the insulation the maximum over voltages could not endanger the winding. A comparison of the results with those of large superconducting fusion coils leads to the recommendation that during the design stage of larger sized SMES a numerical investigation of the resonance behaviour of the system should be performed.
Quantities of a multiterminal circuit determined on the basis of Kirchhoff's laws
Authors: Depenbrock M. 
Published: July 2010

AbstractFor multiterminal electrical networks the interdependency between voltages and currents of the branches of different equivalent circuits and the corresponding terminal quantities are determined using only Kirchhoff's laws. It is shown, that the only set of voltages appertaining to the set ofn currents passing the n terminals consists of the n voltages between the terminals and their common virtual star point, the potential of which is defined to be the mean value of the potentials of all n terminals. In the general case power quantities can be reasonably determined only using pairs which consist either of a terminal current and the appertaining terminal‐to‐virtual star point voltage or of a terminal‐to‐terminal voltage and its appertaining current, the definition of which is less well known. Apparent power is defined to be equal to the physically defined active power, assuming that all terminal currents would be proportional to their appertaining voltages and would have the same collective rms value as the set of actual terminal currents. All definitions can always be applied, including single‐phase and multiphase energy supply systems with or without neutral conductor.
Wavelet‐based approach to network analysis: An introduction
Authors: Gandelli A. , Monti A. , Riva M. 
Published: July 2010

AbstractStarting from recent results of signal processing theory about wavelet analysis the paper presents a proposal for a review of the electrical network theory based on these new mathematical tools. The basic idea is to find the possibility to extend closed‐form approach in the analysis of electrical systems and arrange an extension of traditional impedance parameters to new and more advanced tools.
New invasive method for localisation of harmonic distortion sources in power systems
Authors: Staroszczyk Z. , Mikolajuk K. 
Published: July 2010

AbstractThe presented paper illustrates the invasive method of power‐system identification. It is based on Czarnecki 's ideas to disturb slightly the system and observe its response to find unknown harmonic sources and equivalent linear impedances. The one‐phase system is considered, with a new signal‐processing technique in which instant measurements are based only on two adjacent signal periods. That approach allowed to move differential calculations to the time domain, and to deal with integral Fourier transform, in place of discrete, in frequency domain. The new algorithm allows to increase the S/N ratio, is insensitive to signal time‐shifts and gives correct results in a wide frequency band (5 kHz). Simulation and measurements results are presented and show how accurate the identification can be for short‐time (two periods) and 1 s long observations.
Calculating a new reference point for the iec‐flickermeter
Authors: Mombauer W. 
Published: July 2010

AbstractModern multicycle‐controlled equipment produce voltage fluctuations with repetition rates much higher than the highest frequency for type testing the IEC flickermeter under the standard IEC 61000‐4‐15. In order to equalize all flickermeters it is necessary to add an additional reference point for 33'/? Hz to the standard. The amount of d/%‐values will be evaluated. Reference values for 120‐ V/60‐Hz‐ and 230‐ V/60‐Hz systems have been added.
Arcing faults detection on transmission lines using least error squares technique
Authors: Djurić M. B. , Radojević Z. M. , Terzija V. V. 
Published: July 2010

AbstractIn this paper a new numerical algorithm for arcing faults detection and fault distance calculation is presented. The solution is given in the time domain and for the most frequent single‐phase to ground fault. It was derived by processing the line terminal voltages and currents. The new algorithm can be utilized for blocking the automatic reclosing. A simple square wave arc voltage model was assumed to represent the long arc in free air. The unknown model parameters (the line resistance and inductance, and arc voltage amplitude) were estimated by using “Least Error Squares Technique”. The new algorithm was successfully tested by computer‐simulated and laboratory tests.
A study of corona phenomenon on hybrid AC/DC transmission lines
Authors: Metwally I. A. 
Published: July 2010

AbstractThe factors affecting corona phenomenon on hybrid AC/DC transmission lines are investigated using a single‐phase AC (50 Hz)/single‐pole DC reduced‐scale model. The variation of DC corona current with DC voltage follows the same conventional formula for rod‐to‐plane gaps, where the exponent of conductor height increases with DC voltage, but is slightly affected by interspacing. While the AC corona current is inversely proportional to the conductor height with a power range from 0.7 to 0.8, it also increases with the decrease in interspacing. Afield computation program is used to model both an AC 132‐kV double‐circuit transmission line and analog hybrid lines. The results reveal that hybrid lines cause higher radio noise but the audible noise is nearly the same as or lower than that for the AC double‐circuit lines. The trend of the experimental results is in agreement with the computed number of streamers and electric field profiles.
Vectorial summation of probabilistic current harmonics in power systems: From a bivariate distribution model towards a univariate probability function
Authors: Wang Y. J. , Pierrat L. 
Published: July 2010

AbstractThis paper extends the investigation into the bivariate normal distribution (BND) model which has been widely used to study the asymptotic behaviour of the sum of a sufficiently large number of randomly‐varying harmonic phasors (of the same frequency). Although the BND model is effective and applicable to most problems involving harmonic summation, its main drawback resides in the computation time required to extract the probability density function of the harmonic magnitude from the two‐dimensional BND model. This paper proposes a novel approach to the problem by assimilating the generalized Gamma distribution (GGD) model to the marginal distribution (the magnitude) of the BND using the method of moments. The proposed method can accurately estimate the parameters of the GGD model without time‐consuming calculation. A power system containing ten harmonic sources is taken as an example where the comparison of the Monte‐Carlo simulation, the BND model and the GGD model is given and discussed. The comparison shows that the GGD model approximates the BND model very well.
A precise method for the impedance calculation of a power rail taking into account the skin effect and complex geometry
Authors: Wang Y. J. 
Published: July 2010

AbstractThe method of coupled inductance based on subdivision of conductors is employed in this paper for calculating the impedance of a power rail (also known as the conductor rail or third rail) considering the skin effect and complex geometry. The proposed method also allows the current distribution over the rail cross‐section to be determined. A numerical technique that is able to economize on the number of subconductors required to achieve a prescribed level of accuracy, is also proposed to reduce computation time and matrix dimensions.
Distribution network restoration using mix integer programming method
Authors: Ciric R. M. , Popovic D. S. 
Published: July 2010

AbstractThis paper describes an efficient and robust method and a developed software package for the restoration of radial distribution networks for the purpose of reconstructing normal operating conditions. The proposed methodology uses combined heuristic approach and mix integer programming for solving the network restoration problem. Due to its computational efficiency, this approach can be used in both the planning and operating environments. Important implementional aspects of the methodology and the results of its application on realistic distribution networks are presented.
A new contact design based on a quadrupolar axial magnetic field and its characteristics
Authors: Fink H. , Heimbach M. , Shang W. 
Published: July 2010

AbstractAxial magnetic field (AMF) contacts are applied within vacuum interrupters especially in case of high short‐circuit current. In this paper a new AMF contact design based on a quadrupolar field arrangement and its characteristics are presented. In the first part the basic principle of the new contact design is introduced. This is followed by three‐dimensional field simulations performed with the aid of a Finite‐Element‐program. The magnitude of the axial magnetic flux density, the phase‐shift between current and magnetic flux density, and the current flow within the contact plate are investigated during arcing. The impact of quadrupolar AMF on the arc behaviour during the high current phase is analysed by high‐speed films and pictures of the contact surface after arcing. The interruption performance of the principle has been validated by short‐circuit tests up to 12 kV/63 kA.
Harmonic interaction in capacitor rectifier loads
Authors: Boix O. , Sainz L. , Pedra J. 
Published: July 2010

AbstractIn this paper a steady‐state model of a single‐phase power supply is presented. The model takes into account the influence of feeder harmonic voltages on the non‐linear load behaviour. With this model we can observe that, when the distorting load consumption is important, the harmonic interaction must be considered in order to obtain correct results. This model has been implemented in a harmonic load‐flow program in order to perform harmonic studies in network and industrial installation.
New testing method for the classification of contact materials for vacuum circuit breakers
Authors: Kaumanns J. , Möller K. , Weinert H. 
Published: July 2010

AbstractA new testing method to classify contact materials for high‐current interruption with vacuum circuit breakers (VCB) is described. The testing effort is reduced by diminishing the contact gap and the contact area as well as by an adequate testing circuit. Consequently, the number of experiments can be increased for the benefit of a high statistical certainty in the classification of contact materials. The test results are in good agreement with the results of full‐size short‐circuit current interruption tests carried out in a high‐power testing laboratory with VCB equipped with contact materials classified in the new testing circuit.
Tests and calculations of short‐circuit forces and displacements in high‐voltage substations with strained conductors and droppers
Authors: Stein N. , Meyer W. , Miri A. M. 
Published: July 2010

AbstractForschungsgemeinschaft für Elektrische Anlagen und Stromwirtschaft FCH and DKE UK 121.2 have recently completed an extensive systematic programme of short‐circuit tests on substation bus bars of stranded conductors with and without droppers. The present test series, in continuation of the former studies, comprises 100‐kV and 400‐kV arrangements, applying the relevant parameters of the former. Apart from other variations, different current paths were studied for the arrangements with droppers. The present paper is confined to giving a survey of the 100‐kV arrangements, parameter variations, measurements and test results, as far as they presently relate to the calculation procedure oflEC, CENELEC and D/V/VDE. It is further reported on studies with the Finite‐Element Method (FEM) which show a remarkable comparative accuracy. Finally, the standardized method of IEC 60865‐1 and EN 60865‐1 for the calculation of short‐circuit tensile forces is extended onto arrangements with droppers.
Physical model of the interference immunity of electronic devices and conclusions concerning their testing and operating characteristics
Authors: Bauer H. , Hentschel G. 
Published: July 2010

AbstractSwitching and fault processes in power‐supply systems cause pulse‐shaped disturbances which may stress electronic devices of protection and control systems. For test purposes such disturbances can be simulated. But despite of the constant test conditions the reaction of the device on the disturbance can vary in a certain range. Assuming similar internal structures of protection and control devices the coupling path and the effects of the disturbance are described. The variation in device reaction due to the disturbance is explained on the basis of different models which imitate the impact of the disturbances especially on the logical part of the circuit. By applying sensors with constant threshold the effectiveness (function) of several EMC measures can be evaluated independently from the reaction of the special device.
Numerical modelling for investigation and optimization of a sensor for sensitive partial discharge detection on high‐voltage XLPE cables
Authors: Heinrich R. , Jobava R. , Kalkner W. , Gheonjian A. 
Published: July 2010

AbstractBased on experimental investigations a theoretical model of a sensor for partial discharge (PD) detection on high‐voltage cross‐linked polyethylene (XLPE)‐insulated cables respectively joints has been developed. The model handles radial symmetric sensors and is based on the Finite‐Difference Time‐Domain (FDTD) method in which a cylindrical coordinate system is exploited. The calculation provides field values at each node of the FDTD grid. The field pattern in the cable and sensor at different time steps is used to investigate the coupling mechanism of the sensor. It is also used for parametric studies of the sensor, e. g. the dependence of the sensitivity on geometrical characteristics of the sensor, which is investigated theoretically as well as experimentally. Results of computer simulation are in a good agreement with experimental data derived for such sensors.
Ground‐fault fast transients in modern unit‐connected generators
Authors: Zielichowski M. , Fulczyk M. , Mydlikowski R. 
Published: July 2010

AbstractIn this paper the ground‐fault overvoltages in the circuits of unit‐connected generators during interrupted arcing ground faults in the stator winding of the generator with the neutral grounded through the ground‐fault neutraliser were analysed. Comparative simulation tests of ground‐fault voltages and currents for units with the biggest difference in parameters at the neutralisation coefficient equal to 0.6 were carried out. The currents in all the branches of the equivalent scheme of the unit, the voltage drops on its particular elements and the overvoltage danger were determined. The real changes in the resistance of the ground‐fault arc in the main insulation the stator windings and the real mechanism of its quenching were taken into account.
Improvement of interactions among facts controls
Authors: Lei X. , Buchholz B. , Lerch E. , Povh D. 
Published: July 2010

AbstractInteraction among the FACTS (flexible AC transmission systems) devices in a multi‐machine system can adversely influence the damping properties of individual FACTS devices. In some critical cases, it may even amplify power swings or increase voltage deviations. This paper presents a global tuning method for the FACTS controllers in a multi‐machine system. Based on a non‐linear optimization algorithm implemented in a simulation program, the parameter settings of the FACTS controllers involved can be simultaneously optimized at transient conditions in coping with the non‐linear nature of the power system. By minimizing a non‐explicit target function in which swing characteristics between areas are included, interactions among the FACTS controls at transient conditions in the multi‐machine system are minimized. Two multi‐machine power systems equipped individually with a TCSC (thyristor‐controlled series compensator) and a SVC (static Var compensator) are applied to demonstrate the efficiency of the proposed tuning procedure. The results obtained from simulations validate the improvement in damping of overall power oscillations. The simulations also show that the optimized FACTS controllers are robust in providing adequate damping for a range of conditions on the system.
Effect of dust on discharges in rod‐rod air gaps in the presence of parallel insulating spacer
Authors: Malik N. H. , Qureshi M. I. , Al‐Arainy A. A. 
Published: July 2010

AbstractBreakdown and corona are investigated experimentally in clean and dust‐polluted rod‐rod air gaps in the presence of clean and dust polluted insulating spacer placed parallel to the electrodes. Gap length and spacer distances were varied and DC voltages of both polarities were used to investigate breakdown voltage andpulsa‐tive corona characteristics. The results show that the presence of spacer tends to considerably influence the effects of dust pollution on the breakdown and corona characteristics. Possible mechanisms, which control these variations, are discussed.
Accurate fault location algorithm for power transmission lines
Authors: Sadeh J. , Ranjbar A. M. , Hadjsaid N. , Feuillet R. 
Published: July 2010

AbstractIn this paper we propose a new fault location algorithm for power transmission lines based on one terminal voltage and current data. A distributed time domain model of the line is used as a basis for algorithm development. The suggested technique only takes advantage of post‐fault voltage and current samples taken at one end of the line and does not require filtering of DC offset and high‐frequency components of the recorded signals, which are present during transient conditions. Another advantage of the proposed method is the application of a very narrow window of data i. e. less than 1/4 of a cycle. The paper also proposes two different algorithms for lossless and lossy line models. Computer simulations approved the accuracy of the proposed methods.